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  • 2000-2004  (7)
  • 1995-1999  (121,238)
  • 1985-1989  (13)
  • 1920-1924
  • 1997  (121,238)
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Material
Years
Year
Person/Organisation
Keywords
Language
  • 1
    Electronic Resource
    Electronic Resource
    A measurement of τ polarization in Z^0 decays (1992-8977)
    Amsterdam : Elsevier
    Physics Letters B 294 (1992), S. 466-478 
    Details
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(92)91549-O
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  • 2
    Electronic Resource
    Electronic Resource
    Measurement of the average lifetime of b hadrons (1993-4325)
    Amsterdam : Elsevier
    Physics Letters B 317 (1993), S. 474-484 
    Details
    ISSN: 0370-2693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0370-2693(93)91027-K
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  • 3
    Book
    Book
    Computing : archives for informatics and numerical computation; Supplementum (1977-2003)
    Wien [u.a.] :Springer, ; 1.1977 - 16.2003; damit Ersch. eingest.
    Details
    Title: Computing : archives for informatics and numerical computation; Supplementum
    Publisher: Wien [u.a.] :Springer,
    Year of publication: 1977-2003
    Dates of Publication: 1.1977 - 16.2003; damit Ersch. eingest.
    Type of Medium: Book
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  • 4
    Online Resource
    Online Resource
    Journal of molecular modeling (1996-2002)
    Berlin ; Heidelberg :Springer, ; 1.1995(1996) - 8.2002
    Details
    Title: Journal of molecular modeling
    Publisher: Berlin ; Heidelberg :Springer,
    Year of publication: 1996-2002
    Dates of Publication: 1.1995(1996) - 8.2002
    ISSN: 0949-183X
    Type of Medium: Online Resource
    Language: Undetermined
    Subsequent Title: Forts. ---〉:Journal of molecular modeling
    Note: Kumuliert jeweils den abgeschlossenen Jg. der Internetausg.
    Parallel Title: Druckausg. ---〉:Molecular modeling annual
    URL: http://www.springerlink.com/content/100529
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    Zuse Institute Berlin
  • 5
    Journal/Serial
    Journal/Serial
    SIGBIO newsletter / (from 1969-2001)
    New York, NY :ACM, ; 1.1969 - 7.1975/76; N.S. 1.1976 - 21.2001,1; damit Ersch. eingest.
    Details
    Title: SIGBIO newsletter /
    Author: Association for Computing Machinery / Special Interest Group on Biomedical Computing
    Publisher: New York, NY :ACM,
    Year of publication: 1969-2001
    Dates of Publication: 1.1969 - 7.1975/76; N.S. 1.1976 - 21.2001,1; damit Ersch. eingest.
    ISSN: 0163-5697
    Type of Medium: Journal/Serial
    Language: Undetermined
    Parallel Title: Internetausg. ---〉:Biomedical computing
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  • 6
    Journal/Serial
    Journal/Serial
    ¬The¬ journal of logic programming (from 1984-2000)
    New York, NY :North-Holland, ; 1.1984 - 46.2000
    Details
    Title: ¬The¬ journal of logic programming
    Publisher: New York, NY :North-Holland,
    Year of publication: 1984-2000
    Dates of Publication: 1.1984 - 46.2000
    ISSN: 0743-1066
    Type of Medium: Journal/Serial
    Language: Undetermined
    Subsequent Title: Forts. ---〉:¬The¬ journal of logic and algebraic programming
    Parallel Title: Internetausg. ---〉:¬The¬ journal of logic and algebraic programming
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  • 7
    Journal/Serial
    Journal/Serial
    IEEE concurrency / (from 1997-2000)
    Los Alamitos, Calif. :Soc., ; 5.1997 - 8.2000; damit Ersch. eingest.
    Details
    Title: IEEE concurrency /
    Author: Institute of Electrical and Electronics Engineers / Computer Group
    Publisher: Los Alamitos, Calif. :Soc.,
    Year of publication: 1997-2000
    Dates of Publication: 5.1997 - 8.2000; damit Ersch. eingest.
    ISSN: 1092-3063
    Type of Medium: Journal/Serial
    Language: Undetermined
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  • 8
    E-Resource
    E-Resource
    Medical image analysis CD : an international journal of computer vision, visualization and image- guided intervention in medicine (1996-1999)
    Oxford :Univ. Press, ; 1.1996/97 - 3.1999; damit Ersch. eingest.
    Details
    Title: Medical image analysis CD : an international journal of computer vision, visualization and image- guided intervention in medicine
    Publisher: Oxford :Univ. Press,
    Year of publication: 1996-1999
    Dates of Publication: 1.1996/97 - 3.1999; damit Ersch. eingest.
    ISSN: 1361-8431
    Type of Medium: Electronic Resource
    Language: Undetermined
    Parallel Title: Druckausg. ---〉:Medical image analysis
    Parallel Title: Internetausg. ---〉:Medical image analysis
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  • 9
    Journal/Serial
    Journal/Serial
    CWI quarterly (from 1988-1999)
    Amsterdam :CWI, ; 1.1988 - 12.1999; damit Ersch. eingest.
    Details
    Title: CWI quarterly
    Author: Centrum voor Wiskunde en Informatica 〈Amsterdam〉
    Publisher: Amsterdam :CWI,
    Year of publication: 1988-1999
    Dates of Publication: 1.1988 - 12.1999; damit Ersch. eingest.
    ISSN: 0168-826X , 0922-5366
    Type of Medium: Journal/Serial
    Language: Undetermined
    Former Title: Vorg. ---〉:Centrum voor Wiskunde en Informatica 〈Amsterdam〉: CWI newsletter
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  • 10
    Book
    Book
    Computer personnel : a quarterly publ. of the Special Interest Group on Computer Personnel Research, SIGCPR (1971-1999)
    New York, NY :ACM, ; Nachgewiesen 2.1971 - 20.1999,4; damit Ersch. eingest.
    Details
    Title: Computer personnel : a quarterly publ. of the Special Interest Group on Computer Personnel Research, SIGCPR
    Publisher: New York, NY :ACM,
    Year of publication: 1971-1999
    Dates of Publication: Nachgewiesen 2.1971 - 20.1999,4; damit Ersch. eingest.
    ISSN: 0160-2497
    Type of Medium: Book
    Parallel Title: Internetausg. ---〉:Computer personnel
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  • 11
    Journal/Serial
    Journal/Serial
    Unix review : the publication for the Unix community (from 1983-1998)
    San Francisco, Calif. :Miller Freeman, ; 1.1983 - 16.1998,3
    Details
    Title: Unix review : the publication for the Unix community
    Publisher: San Francisco, Calif. :Miller Freeman,
    Year of publication: 1983-1998
    Dates of Publication: 1.1983 - 16.1998,3
    ISSN: 0742-3136
    Type of Medium: Journal/Serial
    Language: Undetermined
    Subsequent Title: Forts. ---〉:Unix review's performance computing
    Parallel Title: Internetausg. ---〉:Unix review.com
    URL: Zugriff lizenzfrei
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  • 12
    Journal/Serial
    Journal/Serial
    SIGART bulletin : a quarterly publ. of the Special Interest Group on Artificial Intelligence (from 1990-1998)
    New York, NY :ACM, ; 1.1990 - 9.1998
    Details
    Title: SIGART bulletin : a quarterly publ. of the Special Interest Group on Artificial Intelligence
    Author: Association for Computing Machinery / Special Interest Group on Artificial Intelligence
    Publisher: New York, NY :ACM,
    Year of publication: 1990-1998
    Dates of Publication: 1.1990 - 9.1998
    ISSN: 1053-4830
    Type of Medium: Journal/Serial
    Language: Undetermined
    Former Title: Vorg. ---〉:Association for Computing Machinery / Special Interest Group on Artificial Intelligence: SIGART newsletter
    Subsequent Title: Forts. ---〉:Intelligence
    Parallel Title: Internetausg. ---〉:Artificial intelligence
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  • 13
    Journal/Serial
    Journal/Serial
    SIGNUM newsletter (from 1969-1998)
    New York, NY :ACM, ; 4.1969 - 33.1998,2; damit Ersch. eingest
    Details
    Title: SIGNUM newsletter
    Author: Association for Computing Machinery / Special Interest Group on Numerical Mathematics
    Publisher: New York, NY :ACM,
    Year of publication: 1969-1998
    Dates of Publication: 4.1969 - 33.1998,2; damit Ersch. eingest
    ISSN: 0163-5778
    Type of Medium: Journal/Serial
    Former Title: Vorg. ---〉:Association for Computing Machinery / Special Interest Committee on Numerical Mathematics: SICNUM newsletter
    Additional Information: 16,3=3,2 von:Association for Computing Machinery / Technical Committee on Fortran: FORTEC forum
    Parallel Title: Internetausg. ---〉:Numerical mathematics
    URL: Nur Table of Contents.
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  • 14
    Journal/Serial
    Journal/Serial
    Computer networks and ISDN systems : the international journal of computer and telecommunications networking (from 1985-1998)
    Amsterdam [u.a.] :Elsevier [u.a.], ; 9.1985 - 30.1998
    Details
    Title: Computer networks and ISDN systems : the international journal of computer and telecommunications networking
    Publisher: Amsterdam [u.a.] :Elsevier [u.a.],
    Year of publication: 1985-1998
    Dates of Publication: 9.1985 - 30.1998
    ISSN: 0169-7552 , 0376-5075
    Type of Medium: Journal/Serial
    Language: Undetermined
    Subsequent Title: Vorg. u. Forts. ---〉:Computer networks
    Note: Computer networks for research in Europe
    Additional Information: In 14,1=15 von:Networkshop: Conference report
    Additional Information: 16,1/2=4; 17,4/5=5 von:European Networkshop: European Networkshop
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  • 15
    Journal/Serial
    Journal/Serial
    Computers in physics / (from 1987-1998)
    Woodbury, NY :AIP, ; 1.1987,1(Nov./Dez.); 2.1988 - 12.1998
    Details
    Title: Computers in physics /
    Contributer: American Institute of Physics
    Publisher: Woodbury, NY :AIP,
    Year of publication: 1987-1998
    Dates of Publication: 1.1987,1(Nov./Dez.); 2.1988 - 12.1998
    ISSN: 0894-1866
    Type of Medium: Journal/Serial
    Language: Undetermined
    Subsequent Title: Forts. ---〉:Computing in science & engineering
    URL: http://www.aip.org/cip/
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  • 16
    Electronic Resource
    Electronic Resource
    Exact order reduction method in mode conversion problems (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3129-3140 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The exact order reduction method solves the fourth-order system of equations from the Vlasov equations that describe mode conversion by breaking the solution into two steps. The first step is to find the numerical solutions of a pair of second-order equations for the fast waves and slow waves, respectively, which are easily obtained. The second step uses an associated integral equation to obtain the coupling between the fast and slow waves. Potential difficulties due to singularities in the kernel of the integral equations near the axis are resolved by altering the integration path. This allows accurate estimates for mode conversion efficiencies in realistic geometries as the integral equation is solved only in a narrow region near resonance, while the global fast wave solution of the reduced second-order equation covers the entire cross section. The method makes virtually no approximations except that it keeps only the lowest nontrivial order terms in the Larmor radius expansion. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872452
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  • 17
    Electronic Resource
    Electronic Resource
    Turbulization of nonlinear Langmuir oscillations in a cold plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3200-3203 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that the electric field of Langmuir oscillations in a cold plasma contains a component, independent of time, setting ions in motion. Using Lagrange variables, one-dimensional dynamics of plasma in respect to the interaction between electron oscillations and ion movement is investigated. As a consequence of this interaction, the crossing of electron trajectories occurs even at small amplitudes at time tc, i.e., one-dimensional turbulence appears in the system. The expression for tc is derived. In time tc ion displacements as well as ion energy are found to depend only on the electron–ion mass relationship. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872460
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  • 18
    Electronic Resource
    Electronic Resource
    The bootstrap current in a tokamak with electron cyclotron heating (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3211-3216 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The bootstrap current in a non-Maxwellian tokamak plasma with electron cyclotron heating is calculated. The calculation is exact in the limit of highly charged ions, where pitch-angle scattering dominates over quasilinear diffusion, and shows that the current is entirely determined by the pressure of the trapped electrons. If the ion charge is finite, the current is shown to consist of two terms: one driven by collisions, and one driven by the heating and losses. The former is calculated approximately by using a model collision operator, and is found to be determined by the distribution of trapped electrons alone; the latter is discussed qualitatively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872462
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  • 19
    Electronic Resource
    Electronic Resource
    Anomalous width variations for ion acoustic rarefactive solitary waves in a warm ion plasma with two electron temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3204-3210 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Anomalous width–amplitude variations were observed in large amplitude rarefactive solitary waves which show increasing width with increasing amplitude, contrasting the usual reciprocal relation between the square of the width and the amplitude, beyond a certain value of the plasma parameters [S. S. Ghosh, K. K. Ghosh, and A. N. Sekar Iyengar, Phys. Plasmas, 3, 3939 (1996)]. For the limiting maximum amplitude, the "increasing width" solitary wave tends to a double layer-like solution. The overall variation was found to depend crucially on the specific parameter space. From a detailed investigation of the above behavior, a plausible physical explanation has been presented for such increases in the width. It is found that the ions' initial kinetic energies and the cold electron concentration within the perturbed region play a significant role in determining the observed width–amplitude variation. This contradicts the investigation of Sayal, Yadav, and Sharma [Phys. Scr. 47, 576 (1993)]. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872461
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  • 20
    Electronic Resource
    Electronic Resource
    Aspect ratio scaling of toroidal plasma equilibria and the tokamak bootstrap effect (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3254-3261 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The aspect ratio scaling of toroidal plasma equilibria is examined using a parametrization of an exact Solov'ev solution to the Grad–Shafranov equation in Boozer coordinates. The equilibrium analysis suggests that simultaneous enhancements in magnetohydrodynamic (MHD) stability and the bootstrap effect are possible in tight aspect ratio (A→1) tokamaks. The fundamental physical mechanism causing the enhancements is shown to be the natural increase of the MHD safety factor q in tight aspect ratio toroidal geometries. The results of the scaling model suggest that the lowest bootstrap current fractions are obtained in tokamaks with aspect ratios A(approximate)3. It is also shown that a tight aspect ratio bootstrapped tokamak can be a weakly paramagnetic device. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872410
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  • 21
    Electronic Resource
    Electronic Resource
    Resistive pressure gradient-driven turbulence at stellarator plasma edge (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3282-3292 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High resolution calculations of resistive pressure gradient-driven turbulence for the plasma edge parameters of the Advanced Toroidal Facility (ATF) [J. F. Lyon et al., Fusion Technol. 10, 179 (1986)] electron cyclotron heated discharges give fluctuation levels, consistent with the experimental measurements. This turbulence model is also used to simulate the transition from the low confinement to the high confinement mode. The transition is triggered through the poloidal flow amplification induced by the Reynolds stress. After the transition, the confinement improvement is relatively low (30%–40%), even for unrealistically low poloidal viscosity. In the high confinement mode, the characteristic radial scale length of the poloidal flow in the three-dimensional calculations (separation between the lowest-n resonant surfaces) is different from the single helicity results (radial correlation length of the fluctuations). The simple criterion based on the ratio of shearing rate to the linear growth rate does not quantitatively account for the fluctuation reduction. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872469
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  • 22
    Electronic Resource
    Electronic Resource
    Extended neoclassical transport theory for incompressible tokamak plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3320-3322 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conventional neoclassical transport theory is extended to include the effects of orbit squeezing, and to allow the effective poloidal Mach number UpM=[(V(parallel)/vt)+(VEB/vtBp)] of the order of unity for incompressible tokamak plasmas. Here, V(parallel) is the parallel mass flow, vt is the ion thermal speed, VE is the poloidal E×B drift speed, B is the magnetic field strength, and Bp is the poloidal magnetic field strength. It is found that ion thermal conductivity is reduced from its conventional neoclassical value in both banana and plateau regimes if UpM〉1 and S〉1. Here, S=[1+cI2Φ′′/(Ω0B0)] is the orbit squeezing factor with c the speed of light, I=RBt, R the major radius, Φ the electrostatic potential, B0 the magnetic field strength on the axis, Ω0=eB0/Mc, M the ion mass, e the ion charge, Φ′′=d2Φ/dψ2, and ψ the poloidal flux function. However, there is an irreducible minimum for the ion thermal conductivity in the banana-plateau regime set by the conventional Pfirsch–Schlüter transport. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872472
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  • 23
    Electronic Resource
    Electronic Resource
    Studies of instability and transport in sheared-slab plasmas with very weak magnetic shear (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3334-3340 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion temperature gradient (ITG or ηi) driven microinstabilities are studied, using kinetic theory, for tokamak plasmas with very weak (positive or negative) magnetic shear (VWS). The gradient of magnetic shear as well as the effects of parallel and perpendicular velocity shear (v(parallel)′ and vE′) are included in the defining equations. Two eigenmodes: the double (D) and the global (G) are found to coexist. Parametric dependence of these instabilities, and of the corresponding quasilinear transport is systematically analyzed. It is shown that, in VWS plasmas, a parallel velocity shear (PVS) may stabilize or destabilize the modes, depending on the individual as well as the relative signs of PVS and of the gradient of magnetic shear. The quasilinear transport induced by the instabilities may be significantly reduced with PVS in VWS plasmas. The vE′ values required to completely suppress the instabilities are much lower in VWS plasmas than they are in normal plasmas. Possible correlations with tokamak experiments are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872474
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  • 24
    Electronic Resource
    Electronic Resource
    Effect of a wiggler on two-stream instability (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3380-3381 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a plasma-filled free electron laser two-stream instability is a serious consideration. The growth rate of the instability could be significantly reduced by coupling it to the electromagnetic modes/quasimodes through the wiggler. The effect is important near wiggler plasma resonance, where plasma frequency equals the product of wiggler wave number and beam velocity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872478
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  • 25
    Electronic Resource
    Electronic Resource
    A high-efficiency free-electron laser-peniotron hybrid with a longitudinal wiggler magnetic field (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3390-3393 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Stimulated emission from the interaction of a cold, relativistic beam of electrons gyrating in a combined solenoidal and longitudinally polarized periodic wiggler magnetic field is considered as a source of high-efficiency and short-wavelength radiation. The analysis of electron motion in such a combined field shows the motion covers rich Fourier components. The first Fourier component, with the cyclotron frequency of ωc+kwv(parallel), has relatively large transverse velocity compared with the velocity of the motion. The study of the interaction of this Fourier component with the peniotron electromagnetic mode indicates that a high efficiency of 36% is obtained. Its working mechanism is explained and the influence of the wiggler field on the saturation efficiency is analyzed. The electron bunching in the transverse plane and the evolution of the efficiency with the interaction distance is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872480
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  • 26
    Electronic Resource
    Electronic Resource
    Fishbone mode excitation in the ion kinetic regime (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2785-2787 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By solving the dispersion relation in the ion kinetic regime, it is found that the threshold of the plasma beta value for exciting the ion-fishbone mode is lowered. Thus, for most of the present-day tokamaks where the Bussac criterion [Bussac et al., Phys. Rev. Lett. 35, 1638 (1975)] is not satisfied, it will still be possible to excite the ion-fishbone mode. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872445
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  • 27
    Electronic Resource
    Electronic Resource
    Production of sheared flow during ion cyclotron resonance heating in tokamak plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2788-2790 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An approach of producing the poloidal ion rotation by using ion cyclotron resonance heating (ICRH) is presented in core tokamak plasmas. The mechanism employed here is inducing a poloidal density inhomogeneity by rf cyclotron heating and then destabilizing the anomalous Stringer spin-up. A criterion for destabilization of the poloidal ion rotation in the presence of a rf wave is given, which depends on the ratio of the characteristic time of inhomogeneous density formation to the ion collision time. The numerical results have shown that the poloidal ion rotation can be destabilized in the present ICRH power level. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872446
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  • 28
    Electronic Resource
    Electronic Resource
    Rarefactive ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave in a negative ion plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2893-2898 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments on the excitation of rarefactive ion acoustic solitons using a fine mesh grid in a negative ion plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. An interpretation of the velocity modulation and bunching of free-streaming ions that pass through the grid to which the signal is applied is given. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872420
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  • 29
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    Description of turbulent transport in tokamaks by invariants (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2907-2919 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In general, turbulent transport drives a plasma toward a state of turbulent equipartition, in which Lagrangian invariants are uniformly distributed. Different invariants decay with different rates, and in tokamaks the frozen-in law of particles in the poloidal magnetic field survives longer than the corresponding law for the toroidal field, assuming that the trapped particles dominate the turbulent transport. Therefore, the plasma profiles depend on the safety factor q(r), and the condition for convection of trapped particles is that the shear dq/dr is positive. There are two ways to suppress this convection and thereby enhance confinement. The first one is to reverse the magnetic shear. The energy of typical trapped particles then increases outward instead of inward, which suppresses instabilities. The second method is to eliminate the trapped ions by poloidal rotation, and thereby create a transport barrier. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872422
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    Studies of transport scaling and reduction under feedback (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2933-2939 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A feedback control system using an ion beam as a remote suppressor has been previously shown to be very effective in suppressing plasma instabilities in the Columbia Linear Machine [G. A. Navratil et al., Plasma Phys. 24, 184 (1982)]. The first experimental measurements for the effect of this feedback system on anomalous particle transport, as determined from the cross-correlation of density and potential fluctuations is presented. It is shown that feedback reduces transport due to a rotational E×B mode by up to a factor of 3 in this experiment. Also, it was found that particle transport scales linearly with fluctuation amplitude and feedback control does not alter this scaling. Last, the experimentally observed scaling of particle transport does not agree with any theoretical predictions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872425
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    Role of finite parallel wave number in low frequency fluctuations in toroidal current less plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2955-2961 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we present results related to studies of low frequency electrostatic fluctuations in a toroidal plasma of varying length and without a toroidal current. The toroidal length of plasma is varied from fully toroidal (major radius R=45 cm) to 278, 212 and 142 cm. The characteristics of fluctuations changed, showing the effect of finite system length on the nature of the fluctuations. The major results are (1) a drastic reduction in the amplitude of fluctuations, (2) this reduction is mainly due to the disappearance of coherent peaks at 3 kHz and its harmonics observed in unbounded system, (3) the presence of a broad coherent feature around 10 kHz, only in bad curvature region, at low magnetic field (200 G) and (4) the appearance of a large number of coherent peaks, in one particular system length, at a higher magnetic field (400 G). These results indicate that the Rayleigh–Taylor instability with finite k|| may be excitable in the device. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872428
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    Signatures of deuterium recombination in the DIII-D divertor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2989-2996 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thomson scattering measurements performed in the divertor of the DIII-D tokamak [Plasma Physics Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159] during detached operation show that the electron temperatures are typically between 0.8 and 2.0 eV throughout a region which may extend several centimeters above the target plate. At such low temperatures the excitation of recycling deuterium atoms or impurities should be weak. Nevertheless, significant radiation is frequently detected in these locations. It has been suggested that recombination processes, which become important only below about 1.5 eV for deuterium, are responsible for the observed emission. This hypothesis has been investigated by comparing ratios of deuterium lines from attached and detached plasmas with theoretical ratios expected for ionizing or recombining conditions. The analysis of several discharges indicates that the mechanism for production of the emission changes from being collisional excitation of atomic deuterium to a mixture of collisional-radiative recombination and collisional excitation as plasmas evolve from attached to detached states. Localization of D-α emission to low-temperature regions using tangentially viewing camera data together with Thomson scattering results and measurements of deuterium atom temperatures are consistent with these conclusions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872432
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  • 33
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    High-intensity illumination of an exploding foil (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3006-3011 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In an experiment relevant to the fast ignitor fusion concept, a preformed plasma simulating the corona of a fusion target has been probed with laser intensities exceeding 1018 W/cm2. It is seen that the f number of the probe beam is increased as it propagates through the target plasma—a channeling of the power. The transmission and backscatter of the probe beam have been examined, and the analysis suggests anomalous absorption of laser light in shorter scale length plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872435
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  • 34
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    Signatures of target performance and mixing in titanium-doped, laser-driven target implosions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3021-3030 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Absorption-spectroscopy measurements using an embedded titanium layer have been performed on laser implosions of spherical shells. Predicted absorption features formed by the titanium layer were observed: absorption lines due to 1s–2p transitions in titanium ions of incomplete L shell, as well as K-edge absorption in cold titanium. Also observed were oscillations due to EXAFS (Extended X-Ray Absorption Fine Structure) above the Ti K edge. The core temperature and shell areal density and temperature are derived from the measurements and are found to fall short of the values predicted by one-dimensional code simulations. This shortfall is attributed to the lack of irradiation symmetry, which leads to hydrodynamic instability and mixing (smoothing by phase plates was not used in this experiment). Signatures of mixing include the emission of the He-α line of Ti+20 due to titanium migrating to the core, as well as the EXAFS spectrum indicating cold titanium close to peak compression.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872443
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  • 35
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    Particle-in-cell (PIC) simulations of beam instabilities in gyrotrons (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3043-3048 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Extensive simulations are performed to investigate effects of electron cyclotron instabilities on the gyrotron beam quality, using two-dimensional axisymmetric particle-in-cell (PIC) codes. Both electrostatic and electromagnetic models, as well as realistic geometries of the gyrotron, are considered. It is found that a large beam density can lead to an electrostatic-instability-induced energy spread which substantially degrades the gyrotron efficiency. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872439
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  • 36
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    Confinement of a neutral plasma using nested electric potential wells (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2313-2315 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A self-consistent, two-dimensional analysis is presented on confining a region of neutral plasma with a Penning/Malmberg type plasma trap using a nested well configuration. It is found that a neutral plasma region having disparate electron and ion temperatures or having high charge state ions can be confined with static fields. For confining a neutral region comprised of electrons and equal temperature low charge state ions, a quasistatic approach appears promising. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872404
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  • 37
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    Linear stability of the collisionless, large Larmor radius Z-pinch (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2322-2330 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Vlasov fluid model is used to study the m=0 and m=1 internal and free boundary modes in a collisionless, large Larmor radius Z pinch. Two methods (initial value and variational) are employed, and give good agreement. The growth rate can be reduced from its zero Larmor radius value by a factor of up to 10 for m=1, and up to 3 for m=0. Stability thresholds and the role of resonant ions are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872237
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    Impulsive and transient excitation of Bohm–Gross waves in a dissipative plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2336-2347 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Based on the resolution of the partial differential equation describing the external excitation of the Bohm–Gross longitudinal wave, analytical expressions for causal responses of a dissipative macroscopic plasma are derived. Both impulsive and harmonic solutions representing the spatial Green's functions of the radiation problem are given. These exact responses of the plasma, expressed in terms of two-variable Lommel functions, are then used to gain some better understanding of the excitation and dynamics of the well-known thermal wave. Special attention is paid to the resonant excitation case. Intrinsic characteristics of the secular behavior of the radiated signal are illustrated and analyzed. It is shown that the proffered algebraic solutions constitute a generalization of previous results inferred from an asymptotic representation of the Green's functions, or from the familiar steady state harmonic approach. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872239
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  • 39
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    Ion acoustic soliton excitation using a modulated high-frequency sinusoidal wave (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2436-2442 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments on the excitation of ion acoustic solitons using a fine mesh grid in a normal two component plasma are described. The excitation is novel in that a modulated high-frequency sinusoidal wave voltage signal is applied to the grid. The carrier frequency of the high-frequency sinusoidal wave is above the ion plasma frequency. An interpretation of the velocity modulation and bunching of free streaming ions that pass through the grid to which the signal is applied is given. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872224
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    Numerical observation of turbulence enhanced growth rates (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2508-2518 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An enhancement of the velocity diffusion over the quasilinear value is observed in the regime where the autocorrelation time is much smaller than the linear growth time or resonance broadening time. The diffusion enhancement occurs when the resonance broadening time is small compared with the linear growth time. These simulations are self consistent and have enough modes to be in the continuous spectrum limit. That is, even at the initial amplitudes the intermode spacing is sufficiently small that the resonance overlap parameter is large. A possible mechanism for the enhanced diffusion (spontaneous spectrum discretization) is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872230
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  • 41
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    Radiative and three-body recombination in the Alcator C-Mod divertor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2555-2566 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Significant recombination of the majority ion species has been observed in the divertor region of Alcator C-Mod [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)] under detached conditions. This determination is made by analysis of the visible spectrum from the divertor, in particular the Balmer series line emission and the observed recombination continuum, including an apparent recombination edge at ∼375 nm. The analysis shows that the electron temperature in the recombining plasma is 0.8–1.5 eV. The measured volume recombination rate is comparable to the rate of ion collection at the divertor plates. The dominant recombination mechanism is three-body recombination into excited states (e+e+D+⇒D0+e), although radiative recombination (e+D+⇒D0+hν) contributes ∼5% to the total rate. Analysis of the Balmer series line intensities (from nupper=3 through 10) shows that the upper levels of these transitions are populated primarily by recombination. Thus the brightnesses of the Balmer series (and Lyman series) are directly related to the recombination rate. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872234
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  • 42
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    Comments on "Dispersion relation of a plasma in the periodic magnetic field of a wiggler" [Phys. Plasmas 3, 1773 (1996)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2768-2768 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is argued that the equilibrium state of a wiggler background magnetoplasma corresponds to a zero momentum rather than to a plasma acquiring a non-zero velocity. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872398
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    Comment on "Dynamic plasma screening effects on semiclassical inelastic electron–ion collisions in dense plasmas" [Phys. Plasmas 4, 21 (1997)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2770-2771 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Jung's analysis of dynamics screening appears to be flawed by attempting to patch many-body effects into a single-body theory and a more rigorous foundation is necessary. Jung's result and dynamical screening have been previously analyzed many times.(AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872400
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    Comment on "Explanation for MARFE formation and subsequent evolution into a detached symmetric plasma edge" [Phys. Plasmas 3, 2673 (1996)], "MARFE impurity density limits in tokamaks with poloidal asymmetry and rotation" [Phys. Plasmas 3, 3032 (1996)], and "MARFE suppression by external edge heating" [Phys. Plasmas 4, 134 (1997)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2774-2775 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: W. M. Stacey presents stability criteria for the thermal instability based on a linear one-dimensional (1D) slab model including the effects of ionization recombination [Phys. Plasmas 3, 2673 (1996)], large radial gradients and rotation [Phys. Plasmas 3, 3032 (1996)] and external edge heating [Phys. Plasmas 4, 134 (1997)]. The second paper is incorrectly presented as a two-dimensional (2D) analysis. The hypothesis for the poloidal asymmetry of the multifaceted asymmetric radiation from the edge (MARFE) is based on a misinterpretation of the linear results and contradicted by our own linear analyses in a 1D cylindrical [Phys. Plasmas 1, 2623 (1994)] and a 2D tokamak model [Plasma Phys. Controlled Fusion 39, 423 (1997)]. The explanation for the evolution into a detached plasma and for MARFE suppression by external edge heating are interesting hypotheses, supported by experimental observations. However, a 1D linear analysis does not offer the basis to support these hypotheses theoretically.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872401
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  • 45
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    Enhanced coupling of the fast wave to electrons through mode conversion to the ion hybrid wave (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2031-2043 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An analysis of ion cyclotron resonance heating in a plasma containing two ion species is given. Particular emphasis is placed on the important case of comparable concentrations of the two species. The properties of ion-Bernstein waves in such a plasma are discussed. A summary of the cutoff–resonance (Budden) and cutoff–resonance–cutoff (triplet) configurations is given and an analytic expression obtained for the Budden transmission coefficient (relevant also to the triplet case), which is valid for any concentration ratio of the two-ion species. A formula for the damping coefficient of the ion hybrid wave is obtained and a ray tracing code is used to illustrate the absorption of this mode by electrons close to the two-ion hybrid resonance. The reduced, second-order fast wave equation is solved numerically, illustrating the transition from strong electron heating through mode conversion at the two-ion hybrid resonance to direct electron damping of the fast wave in a high beta plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872369
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  • 46
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    Diamagnetism in a plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2072-2080 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This is an extension of a study of electric currents and force balance orthogonal to a unidirectional magnetic field of induction (B) in a collisionless plasma [K. D. Cole, Phys. Plasmas 3, 2717 (1996)]. All quantities are assumed to vary only in one direction orthogonal to B. Two new concepts are introduced, which are not in conventional plasma physics. First a magnetic polarization effect corresponding to electric polarization is found. This defines a contribution to the magnetic moment per unit volume of −ρmc2E2/B3. Second the conduction current is defined in terms of the curl of the magnetic field intensity H, in accordance with Maxwell. In this scheme, when there is no electric field, (1/4π)(∂H/∂z)B+(∂p⊥/∂z)=0, instead of the conventional equation with B/μ0 in place of H. In both schemes, j×B−(bold del)p⊥=0. Though this makes no difference to the electric current intensity calculated in the two schemes, and no difference to the force balance equation, it makes a significant difference to the relationship between B and p⊥ in many plasma conditions of interest. When the electric field is nonzero, the situation is more complex. It is shown that the new diamagnetism of this paper and the dielectric current of the earlier one are consistent with special relativity. Some applications of the theory are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872373
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  • 47
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    Explosion of soliton in a multicomponent plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2095-2100 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional nonlinear Kadomtsev–Petviashvili (K–P) wave equation is derived to discuss the solitons in multicomponent plasma contaminated with negative ions. A new formalism of the simple wave solution method is developed for finding the soliton behaviors caused by the presence of negative ions in plasmas. It is seen that the nonlinear wave equation leads, in some cases, to an ordinary differential equation and a straight way for solving the soliton propagation in plasmas. The overall observations describe the natures of compressive and rarefactive solitons along with the shock-like wave caused by the interaction of negative ions. Also discussed are the possible controls of the scenarios of soliton behaviors. Moreover it is believed, from present investigations, that the observations of collapses or explosions in solitons could enhance the understanding of the soliton phenomena in laboratory and space plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872545
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    Statistical theory of resistive drift-wave turbulence and transport (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2116-2133 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Resistive drift-wave turbulence in a slab geometry is studied by statistical closure methods and direct numerical simulations. The two-field Hasegawa–Wakatani (HW) fluid model, which evolves the electrostatic potential and plasma density self-consistently, is a paradigm for understanding the generic nonlinear behavior of multiple-field plasma turbulence. A gyrokinetic derivation of the HW model is sketched. The recently developed Realizable Markovian Closure (RMC) is applied to the HW model; spectral properties, nonlinear energy transfers, and turbulent transport calculations are discussed. The closure results are also compared to direct numerical simulation results; excellent agreement is found. The transport scaling with the adiabaticity parameter, which measures the strength of the parallel electron resistivity, is analytically derived and understood through weak- and strong-turbulence analyses. No evidence is found to support previous suggestions that coherent structures cause a large depression of saturated transport from its quasilinear value in the hydrodynamic regime of the HW model. Instead, the depression of transport is well explained by the spectral balance equation of the (second-order) statistical closure when account is taken of incoherent noise. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872377
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    Nonlinear dynamics of a beam-driven magnetic plasma: Streaming or mass motion (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2146-2150 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Explicit results pertaining to nonlinear oscillations in a magnetoactive beam–plasma system that shows transient or streaming phenomena are analytically presented. The nonlinear differential equation is formulated and solved in terms of a modified elliptic integral of motion. The phase-space mappings, and their striking features both in strong streaming and nonstreaming situations, are shown. The new features concerning streaming plasma analysis are illustrated in the form of frequency modulation, especially at the onset of chaos. The diminishing trend of modulated frequency in the strong streaming regions is concluded. The findings may have important implications for magnetospheric and cosmic plasma settings where beam plasma interactions exist. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872625
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  • 50
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    The influence of fast ions on the magnetohydrodynamic stability of negative shear profiles (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2181-2187 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of energetic ions on the stability of ideal double kink modes in a tokamak plasma with negative magnetic shear is investigated. It is found that the fast ions play a similar role as for the ordinary m=n=1 internal kink. In particular, phenomena analogous to sawtooth stabilization and fishbone excitation are possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872381
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    Frequency dependent effects in helicon plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2741-2747 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Variations in the plasma parameters of a large volume, helicon source as a function of applied rf power (0–2 kW), driving frequency (8–18 MHz), magnetic field (0–1.4 kG) and fill pressure (2–10 mTorr) have been studied. The transitions between the capacitive, inductive, and resonant helicon mode are consistent with previous experiments. Our data indicate that the transition to the helicon mode occurs at a unique magnetic field, independent of the driving frequency. Based on the helicon wave dispersion relation, from which helicon wavelengths can be calculated, the observed variations in plasma density as a function of driving frequency suggest that the wavelength of the helicon wave is a weak function of driving frequency. Calculation of the electron energies which correspond to the phase velocity of the driving wave (i.e., Landau damping) suggest that either Landau damping cannot be responsible for the efficient ionization of helicon sources, or that the helicon portion of the discharge does not extend over the entire radius of the apparatus. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872142
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    Modeling ionization by helicon waves (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2748-2755 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The response of the electron distribution function in one dimension to a traveling wave electric field is modeled for parameters relevant to a low-pressure helicon wave plasma source, and the resulting change in the ionization rate calculated. This is done by calculating the trajectories of individual electrons in a given wave field and assuming no collisions to build up the distribution function as the distance from the antenna is increased. The ionization rate is calculated for argon by considering the ionization cross section and electron flux at a specified position and time relative to the left-hand boundary, where the distribution function is assumed to be Maxwellian and the wave travels to the right. The simulation shows pulses in the ionization rate that move away from the antenna at the phase velocity of the wave, demonstrating the effect of resonant electrons trapped in the wave's frame of reference. It is found that the ionization rate is highest when the phase velocity of the wave is between 2 and 3×106 m/s, where the electrons interacting strongly with the wave (i.e., electrons with velocities inside the wave's "trapping width") have initial energies just below the ionization threshold. Results from the model are compared with experimental data and show reasonable qualitative agreement. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872143
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    Dynamic plasma screening effects on electron capture process in hydrogenic ion–fully stripped ion collisions in dense plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2756-2759 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In dense plasmas, dynamic plasma screening effects are investigated on electron capture from hydrogenic ions by past fully stripped ions. The classical Bohr–Lindhard model has been applied to obtain the electron capture probability. The interaction potential in dense plasmas is represented in terms of the longitudinal dielectric function. The classical straight-line trajectory approximation is applied to the motion of the projectile ion in order to visualize the electron capture probability as a function of the impact parameter, projectile energy, and plasma parameters. The electron capture probability including the dynamic plasma screening effect is always greater than that including the static plasma screening effect. When the projectile velocity is smaller than the electron thermal velocity, the dynamic polarization screening effect becomes the static plasma screening effect. When the projectile velocity is greater than the plasma electron thermal velocity, the interaction potential is almost unshielded. The difference between the dynamic and static plasma screening effects is more significant for low energy projectiles. It is found that the static screening formula obtained by the Debye–Hückel model overestimates the plasma screening effects on the electron capture processes in dense plasmas. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872144
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    Neoclassical transport in an annular penning trap (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2760-2762 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A modified Penning trap is described with an annular confinement region and a toroidal magnetic field. A non-neutral electron plasma is confined axially by an electrostatic field and, in the radial direction, particles are constrained to lie within a small drift distance of a cylindrical flux surface. Drift orbits of all particles are banana-shaped and collisions cause neoclassical transport. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872145
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    Response to "Comments on ‘Dispersion relation of a plasma in the periodic magnetic field of a wiggler' " [Phys. Plasmas 3, 1773 (1996)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2769-2769 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is argued that a wiggler plasma may acquire a non-zero velocity in the equilibrium and that it should be somehow consistent with the conservation of energy. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872399
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    Response to "Comment on ‘Dynamic plasma screening effects on semiclassical inelastic electron–ion collisions in dense plasmas' " [Phys. Plasmas 4, 21 (1997)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2772-2773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We used a semiclassical technique to calculate the interaction energy between the electron (velocity v) and the target electron by including the dynamic screening effect and effects on atomic transition processes. This differs from previous work. (AIP)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872407
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    Erratum: "Current driven nonlinear Langmuir structures in plasmas" [Phys. Plasmas 4, 230 (1997)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2778-2778 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872622
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    Alfvén wave forces, affecting the tokamak edge plasma in the presence of impurities or dust (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3436-3438 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dust particles appear on the edge of tokamak plasmas as a result of disruptions and plasma interactions with divertor plates, limiters, or blankets, as well as of pellet injections. It is shown that the presence of the dust impurities can lead to an effective decrease of the slow Alfvén wave absorption in the region. These waves are used for heating, current drive, and control of the low-to-high (L–H) confinement transition. Radio-frequency forces can also be strongly changed in the presence of dust particles. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872488
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  • 59
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    Comment on "Two-dimensional solitary kinetic Alfvén waves and dipole vortex structures" [Phys. Plasmas 4, 611 (1997)] (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 3445-3446 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872490
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    An electrostatic magnetohydrodynamics theory for resistive-viscous helical instabilities of arc discharges (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2791-2797 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simplified linear analysis for resistive-viscous magnetic helical instabilities of arc discharges in a cylindrical plasma is developed. Based on a set of electrostatic magnetohydrodynamic (MHD) equations, resistive-viscous m=1 modes with an external axial magnetic field are studied. Explicit analytic results are obtained, from which the growth rate and the stability criterion can be shown, and the electrostatic assumption can be justified. In comparison with the previous channel model calculations, this analytic treatment can provide a simplified model for instability estimates, while avoiding artificial assumptions and misorderings in the energy equation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872411
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    Electric field spikes formed by electron beam–plasma interaction in plasma density gradients (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2805-2812 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the electron beam–plasma interaction at an electric double layer the beam density is much higher than in the classical beam–plasma experiments. The wave propagation takes place along the density gradient that is present at the high potential side of the double layer. Such a case is studied experimentally by injecting the electron beam from a plane cathode, without any grids suppressing the gradient, and by particle simulations. The high frequency field concentrates in a sharp "spike" with a half width of the order of one wavelength. The spike is found to be a standing wave surrounded by regions dominated by propagating waves. It forms at a position where its frequency is close to the local plasma frequency. The spike forms also when the electric field is well below the threshold for modulational instability, and long before a density cavity is formed in the simulations. Particle simulations reveal that, at the spike, there is a backward traveling wave that, when it is strongly damped, accelerates electrons back towards the cathode. In a simulation of a homogeneous plasma without the density gradient no spike is seen, and the wave is purely travelling instead of standing. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872413
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    Frequency dependence of the plasma density for helicon plasmas (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1463-1467 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Variations of plasma density are investigated as a function of frequency of rf power in a helicon plasma source. Abrupt, almost step-like changes in the plasma density are observed during the frequency scans under various conditions of the input rf power, the argon gas pressure, and the magnetic field. It is found that the transition frequencies shift to the lower value region as the input rf power and/or the argon gas pressure is increased, and to the higher value region as the magnetic field is increased. The observed density transitions are compared with semianalytical calculations based on the power balance relation and it has been shown that the results are in good agreement. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872325
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    Dynamics of plasma containing a population of negatively charged heavy vortex elements (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1484-1485 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Due to the presence of a population of heavy, negatively charged vortex elements, plasma becomes birefringent to a low frequency circularly polarized wave of infinitesimally small amplitude. The right circular polarization part remains dispersive whereas the left circular polarization part decays if the rotation associated with the vorticity is anticlockwise as seen by an observer looking antiparallel to the direction of the axis of rotation. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872321
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    Antimatter plasmas and antihydrogen : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1528-1543 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent successes in confining antimatter in the form of positron and antiproton plasmas have created new scientific and technological opportunities. Plasma techniques have been the cornerstone of experimental work in this area, and this is likely to be true for the foreseeable future. Work by a number of groups on trapping antimatter plasmas is summarized, and an overview of the promises and challenges in this field is presented. Topics relating to positron plasmas include the use of positrons to study the unique properties of electron–positron plasmas, the interaction between positrons and ordinary matter, and the laboratory modeling of positron-annihilation processes in interstellar media. The availability of cold, trapped antiprotons and positrons makes possible the production of neutral antimatter in the form of antihydrogen. This is expected to enable precise comparisons of the properties of matter and antimatter, including tests of fundamental symmetries and the measurement of the interaction of antimatter with gravity. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872284
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    Origin of diffusion in Hamiltonian dynamics : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1576-1581 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Without invoking any kind of "loss of memory" hypothesis, a diffusion equation is derived for the Hamiltonian dynamics defined by H=p2/2+(K/4π2)∑m=−MM cos(q−mt+cursive-phim), where the cursive-phims are fixed random phases. The key point of the derivation is a property of locality for the waves inducing transport. Using perturbation theory, it is shown that only waves whose phase velocities satisfy |m−p(t)|≤α(K/4π2)2/3, where α is a constant, approximately 5, play a relevant role for the statistical properties of the dynamics. This implies scaling properties for the dynamics, and leads to the understanding of the origin of force decorrelation and of diffusion, and to the prediction of their occurrence in time. Moreover, the convergence of the diffusion coefficient to its quasilinear value when K→∞ is shown, and is interpreted as the consequence of the crossover between two regimes of decorrelation that are of different natures. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872288
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    Test particle transport from long-range collisions : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1552-1558 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Enhanced cross-magnetic-field diffusion of test particles in pure ion plasmas has been measured. The ion plasma is contained in a Penning-Malmberg trap for weeks near thermodynamic equilibrium, characterized by rigid rotation and uniform density and temperature. Plasma expansion and loss is suppressed by a "rotating wall" technique, i.e., a weak electrostatic potential rotating faster than the plasma. Test particle transport is then measured even though there is zero net transport, in a regime where neutral collisions are negligible. The observed test particle transport is diffusive, i.e., proportional to the gradient of the test particle concentration. The measured diffusion coefficients scale as nT−1/2B−2 over a range of 40 in density, 50 in temperature, and 5 in magnetic field. This diffusion is about ten times greater than predicted by classical collisional theory, which describes velocity-scattering collisions with impact parameters ρ(approximately-less-than)rc. The enhanced transport is thought to be due to non-velocity-scattering "E×B drift" collisions with rc〈ρ(approximately-less-than)λD. Initial estimates of diffusion due to these long-range collisions are three times less than the measurements, and substantial theory questions remain. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872359
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    The stability of advanced operational regimes on the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1589-1595 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of the Tokamak Fusion Test Reactor [D. Meade and the TFTR Group, in Plasma Physics and Controlled Nuclear Fusion Research, Washington, D.C., 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. I, pp. 9–24], as defined by the maximum fusion power production, has been limited, not by confinement, but by stability to pressure-driven modes. Two classes of current profile modification have been investigated to overcome this limit. A new technique has been developed to increase the internal inductance of low-q (q(approximate)4), high-current (Ip〉2MA) plasmas. As was the case at higher edge q, the disruptive β limit has been found to increase roughly linearly with the internal inductance, li. Plasmas with hollow current profiles, i.e., reversed shear, are also predicted and experimentally observed to have increased stability in the negative shear region to ballooning and kink modes. However, performance of these plasmas is still limited by pressure-driven modes in the normal shear region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872290
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    Recent progress in the design of stellarator experiments : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1617-1622 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To evaluate stellarators as power plants, a helias configuration was developed by running high performance computer codes written at New York University. A modular coil set was found that had ample spacing for a reactor and took advantage of the concept of quasihelical symmetry. Since that time, the design has been further optimized and a similar stellarator has been discovered that has just two field periods and a plasma with the low aspect ratio 3.5. Its principal advantage is that in a flux coordinate system its magnetic-field structure comes close to having axial symmetry, so transport is predicted to be almost as good as that in a tokamak at high temperatures. Only 16 moderately twisted coils are required to produce the external magnetic field, and the configuration might well be viewed as a steady-state tokamak rather than an alternate concept. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872292
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    Fivefold confinement time increase in the Madison Symmetric Torus using inductive poloidal current drive : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1632-1637 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current profile control is employed in the Madison Symmetric Torus [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed field pinch to reduce the magnetic fluctuations responsible for anomalous transport. An inductive poloidal electric-field pulse is applied in the sense to flatten the parallel current profile, reducing the dynamo fluctuation amplitude required to sustain the equilibrium. This technique demonstrates a substantial reduction in fluctuation amplitude (as much as 50%), and improvement in energy confinement (from 1 to 5 ms); a record low fluctuation (0.8%) and record high temperature (615 eV) for this device were observed simultaneously during current drive experiments. Plasma beta increases by 50% and the Ohmic input power is three times lower. Particle confinement improves and plasma impurity contamination is reduced. The results of the transient current drive experiments provide motivation for continuing development of steady-state current profile control strategies for the reversed field pinch. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872324
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    High β produced by neutral beam injection in the START (Small Tight Aspect Ratio Tokamak) spherical tokamak : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1665-1671 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The world's first high-power auxiliary heating experiments in a tight aspect ratio (or spherical) tokamak have been performed on the Small Tight Aspect Ratio Tokomak (START) device [Sykes et al., Nucl. Fusion 32, 694 (1992)] at Culham Laboratory, using the 40 keV, 0.5 MW Neutral Beam Injector loaned by the Oak Ridge National Laboratory. Injection has been mainly of hydrogen into hydrogen or deuterium target plasmas, with a one-day campaign to explore D→D operation. In each case injection provides a combination of higher density operation and effective heating of both ions and electrons. The highest β values achieved to date in START are volume average βT∼11.5% and central beta βO∼50%. Already high, these values are expected to increase further with the use of higher beam power. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872271
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    Impurity screening in Ohmic and high confinement (H-mode) plasmas in the Alcator C-Mod tokamak : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1681-1689 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments has been carried out to determine the relative screening of the low recycling gaseous impurities, nitrogen and methane, in Alcator C-Mod tokamak [Phys. Plasmas 1, 1511 (1994)] discharges. The impurity density in the core plasma is directly proportional to the rate of impurity injection. Screening was found to vary weakly with plasma density but to be markedly dependent on the poloidal position of injection. Detachment of the plasma results in significantly less screening both in Ohmic and in high confinement (H-mode) discharges, particularly when the gas is injected into the divertor or at the inner vessel wall. Evidence of impurity transport from the scrape-off layer into the divertor using bolometry and visible spectroscopy is presented and modeling of the transport using a two-dimensional Monte Carlo code is described. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872365
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    High performance Joint European Torus (JET) plasmas for deuterium–tritium operation with the MkII divertor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1725-1735 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Planned experiments in the Joint European Torus [Plasma Physics and Controlled Fusion Research, Proceedings, 13th International Conference, Washington, D.C., 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 1, p. 27] (JET) with deuterium–tritium (D–T) plasmas require high fusion performance for α-particle heating studies and for investigation of isotope dependence in conditions relevant to the International Thermonuclear Experimental Reactor [Plasma Phys. Controlled Fusion 37, A19 (1995)]. In deuterium plasmas, the highest neutron rates have been obtained in the hot-ion high-confinement mode (H mode) which is ultimately limited by magnetohydrodynamic (MHD) phenomena when the pressure gradient approaches ideal ballooning and kink stability limits in the vicinity of the edge transport barrier. Results are reported confirming the MkII divertor's increased closure and pumping in this regime, progress in understanding the MHD-related termination is discussed, and the use of ion cyclotron resonance heating (ICRH) in combination with high-power neutral beams to increase the neutron yield is described. In separate experiments internal transport barriers have been established through careful programming of the current ramp and heating waveforms, and neutron emission comparable with the best hot-ion H-modes achieved. Steady-state H-mode discharges exhibiting edge localized modes (ELMs) in reactor-like configurations and conditions have been demonstrated, including cases in which relevant dimensionless parameter values are preserved, ready also for testing in D–T. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872361
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    Investigation of physical processes limiting plasma density in high confinement mode discharges on DIII-D : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1752-1760 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments was conducted on the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] to investigate the physical processes which limit density in high confinement mode (H-mode) discharges. The typical H-mode to low confinement mode (L-mode) transition limit at high density near the empirical Greenwald density limit [M. Greenwald et al., Nucl. Fusion 28, 2199 (1988)] was avoided by divertor pumping, which reduced divertor neutral pressure and prevented formation of a high density, intense radiation zone (MARFE) near the X-point. It was determined that the density decay time after pellet injection was independent of density relative to the Greenwald limit and increased nonlinearly with the plasma current. Magnetohydrodynamic (MHD) activity in pellet-fueled plasmas was observed at all power levels, and often caused unacceptable confinement degradation, except when the neutral beam injected (NBI) power was ≤3 MW. Formation of MARFEs on closed field lines was avoided with low safety factor (q) operation but was observed at high q, qualitatively consistent with theory. By using pellet fueling and optimizing discharge parameters to avoid each of these limits, an operational space was accessed in which density ∼1.5×Greenwald limit was achieved for 600 ms, and good H-mode confinement was maintained for 300 ms of the density flat-top. More significantly, the density was successfully increased to the limit where a central radiative collapse was observed, the most fundamental density limit in tokamaks. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872277
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    Spatio-temporal dynamics of the resonantly excited relativistic plasma wave driven by a CO2 laser (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1434-1447 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of a relativistic plasma wave (RPW) resonantly excited by a two frequency CO2 laser pulse and the effects of this wave on a co-propagating relativistic electron beam were studied through experiments and supporting simulations. The amplitude of the RPW and its harmonics were resolved in time and space with a Thomson scattering diagnostic. In addition, the plasma wave amplitude-length product and temporal duration were independently measured through time and frequency resolved forward scattering. The transverse electric and magnetic fields associated with the RPW were studied by the scattering of a 2 MeV electron beam, and the eventual heating of the plasma after the breakup of the RPW was measured from the x-ray radiation spectrum. The experiments and simulations show that the RPW reaches a peak amplitude of approximately 30%, with the amplitude limited by plasma blowout driven by the radial ponderomotive forces of the plasma wave. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872318
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    On the Bernstein–Landau paradox (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2497-2507 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The essence of the Bernstein–Landau paradox is that in a stable unmagnetized plasma electrostatic waves exhibit collisionless Landau damping, while in a magnetized plasma the Bernstein modes, perpendicular to the magnetic field, are exactly undamped, independent of the strength of the magnetic field. This problem is the subject of the present study. An analytical solution of the initial value problem for perturbations perpendicular to the magnetic field is given, which is a generalization of the well-known Landau work to magnetized plasmas. By introducing, according to Plemelj's prescription, plus- and minus-functions, having unique analytical properties, the character of the short-term and long-term plasma response is revealed, showing in the small magnetic field limit Landau damping in the first gyroperiod, followed by recurrence, and exhibiting irregular behavior with no damping at large times. The initial damping rate is seen to be close to the commonly used Landau damping rate for unmagnetized plasmas, however with a significant systematic deviation. A corrected expression for the Landau damping rate is found which yields a perfect description of the initial damping of oscillations perpendicular to a weak magnetic field. An alternative approach, expansion over Bernstein modes, is also employed. It is found that a zero-frequency (convective) mode, revealed earlier in particle simulations, is included in the complete linear treatment. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872229
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  • 76
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    Beta limits in long-pulse tokamak discharges : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1654-1664 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The maximum normalized beta achieved in long-pulse tokamak discharges at low collisionality falls significantly below both that observed in short pulse discharges and that predicted by the ideal MHD theory. Recent long-pulse experiments, in particular those simulating the International Thermonuclear Experimental Reactor (ITER) [M. Rosenbluth et al., Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1995), Vol. 2, p. 517] scenarios with low collisionality νe*, are often limited by low-m/n nonideal magnetohydrodynamic (MHD) modes. The effect of saturated MHD modes is a reduction of the confinement time by 10%–20%, depending on the island size and location, and can lead to a disruption. Recent theories on neoclassical destabilization of tearing modes, including the effects of a perturbed helical bootstrap current, are successful in explaining the qualitative behavior of the resistive modes and recent results are consistent with the size of the saturated islands. Also, a strong correlation is observed between the onset of these low-m/n modes with sawteeth, edge localized modes (ELM), or fishbone events, consistent with the seed island required by the theory. We will focus on a quantitative comparison between both the conventional resistive and neoclassical theories, and the experimental results of several machines, which have all observed these low-m/n nonideal modes. This enables us to single out the key issues in projecting the long-pulse beta limits of ITER-size tokamaks and also to discuss possible plasma control methods that can increase the soft β limit, decrease the seed perturbations, and/or diminish the effects on confinement. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872270
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    The role of the neutral beam fueling profile in the performance of the Tokamak Fusion Test Reactor and other tokamak plasmas : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1699-1706 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Scalings for the stored energy and neutron yield, determined from experimental data, are applied to both deuterium-only and deuterium–tritium plasmas in different neutral-beam-heated operational domains in the Tokamak Fusion Test Reactor [Nucl. Fusion 25, 1167 (1985)]. The domain of the data considered includes the Supershot, high poloidal beta, low-mode, and limiter high-mode operational regimes, as well as discharges with a reversed magnetic shear configuration. The new important parameter in the present scaling is the peakedness of the heating beam fueling profile shape. Ion energy confinement and neutron production are relatively insensitive to other plasma parameters compared to the beam fueling peakedness parameter and the heating beam power when considering plasmas that are stable to magnetohydrodynamic modes. However, the stored energy of the electrons is independent of the beam fueling peakedness. The implication of the scalings based on this parameter is related to theoretical transport models such as radial electric field shear and ion temperature gradient marginality models. Similar physics interpretation is provided for beam heated discharges on other major tokamaks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872272
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  • 78
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    Large orbit neoclassical transport : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1707-1713 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neoclassical transport in the presence of large ion orbits is investigated. The study is motivated by the recent experimental results that ion thermal transport levels in enhanced confinement tokamak plasmas fall below the "irreducible minimum level" predicted by standard neoclassical theory. This apparent contradiction is resolved in the present analysis by relaxing the basic neoclassical assumption that the ions orbital excursions are much smaller than the local toroidal minor radius and the equilibrium scale lengths of the system. Analytical and simulation results are in agreement with trends from experiments. The development of a general formalism for neoclassical transport theory with finite orbit width is also discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872273
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  • 79
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    Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1714-1724 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 2, 2176 (1995)] have explored several novel regimes of improved tokamak confinement in deuterium–tritium (D–T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high li). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (qa(approximate)4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-li plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D–T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D–T plasmas with q0〉1 and weak magnetic shear in the central region, a toroidal Alfvén eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872274
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  • 80
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    The two-dimensional structure of radiative divertor plasmas in the DIII-D tokamak : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1761-1773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent measurements of the two-dimensional (2-D) spatial profiles of divertor plasma density, temperature, and emissivity in the DIII-D tokamak [J. Luxon et al., in Proceedings of the 11th International Conference on Plasma Physics and Controlled Nuclear Fusion (International Atomic Energy Agency, Vienna, 1987), p. 159] under highly radiating conditions are presented. Data are obtained using a divertor Thomson scattering system and other diagnostics optimized for measuring the high electron densities and low temperatures in these detached divertor plasmas (ne≤1021 m−3, 0.5 eV≤Te). D2 gas injection in the divertor increases the plasma radiation and lowers Te to less than 2 eV in most of the divertor volume. Modeling shows that this temperature is low enough to allow ion–neutral collisions, charge exchange, and volume recombination to play significant roles in reducing the plasma pressure along the magnetic separatrix by a factor of 3–5, consistent with the measurements. Absolutely calibrated vacuum ultraviolet spectroscopy and 2-D images of impurity emission show that carbon radiation near the X-point, and deuterium radiation near the target plates contribute to the reduction in Te. Uniformity of radiated power (Prad) (within a factor of 2) along the outer divertor leg, with peak heat flux on the divertor target reduced fourfold, was obtained. A comparison with 2-D fluid simulations shows good agreement when physical sputtering and an ad hoc chemical sputtering source (0.5%) from the private flux region surface are used. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872278
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  • 81
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    Gyrofluid simulations of turbulence suppression in reversed-shear experiments on the Tokamak Fusion Test Reactor : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1792-1799 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The confinement improvement in reversed-shear experiments on the Tokamak Fusion Test Reactor [Plasma Phys. Controlled Fusion 26, 11 (1984)] is investigated using nonlinear gyrofluid simulations including a bounce-averaged trapped electron fluid model. This model includes important kinetic effects for both ions and electrons, and agrees well with linear kinetic theory. Both reversed shear and the Shafranov shift reverse the precession drifts of a large fraction of the trapped electrons, which significantly reduces the growth rate of the trapped electron mode, found to be the dominant instability in the core. Two positive feedback transition mechanisms for the sudden improvement in core confinement are discussed: (1) Shafranov shift suppression of the trapped electron mode, and (2) turbulence suppression by radially sheared E×B flows. While both effects appear to be playing roles in the transition dynamics in most experiments, we show that Shafranov shift stabilization alone can cause a transition. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872279
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  • 82
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    Linear waves and instabilities in thermally anisotropic two-component magnetohydrodynamics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2044-2051 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The paper analyzes low-frequency waves in a plasma model that is made up of two thermally anisotropic magnetohydrodynamic components, by means of wave-front diagrams, a useful tool that has not attracted the desired attention. The wave-front diagrams of the fast propagating suprathermal mode, besides the usual fast, slow, and Alfvén modes, have been plotted for a variety of situations. These diagrams are used to bring out the physical significance of the anisotropic model vis-à-vis the isotropic model. The question of stability that has been completely ignored so far in the plasma models based on two magnetohydrodynamic components has also been addressed. Analogues of the firehose and mirror instabilities, which are supported by this model, are examined. Their comparison with single-component anisotropic plasma results suggests the possibility of suppressing the mirror instability. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872370
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  • 83
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    Sawtooth oscillations in a damped/driven cryogenic electron plasma: Experiment and theory (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2062-2071 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements have been made of nonlinear sawtooth oscillations of the displacement of a magnetized electron column in a cryogenic, cylindrical trap. First reported 7 years ago, these oscillations occur when the displacement is destabilized by a resistive wall and damped by a temperature-dependent collisional viscosity. A typical evolution can last for thousands of seconds. Measurements show that oscillations of the plasma displacement are accompanied by oscillations in the plasma temperature. A simple predator-and-prey model of the temperature and displacement gives rise to a limit cycle solution due to the nonmonotonic dependence of the viscosity on temperature. These limit cycles are in good quantitative agreement with the measured sawtooth oscillations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872372
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  • 84
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    Extensions and applications of the Bogema–Davidson inversion theorem (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2090-2094 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For a single particle species confined by a uniform magnetic field B, the Bogema–Davidson inversion theorem determines a self-consistent rigid-rotor equilibrium distribution function F(H⊥−ωrPθ) as the derivative of the given radial density profile n(r) with respect to the corresponding generalized potential ψ(r). Aside from the quadratic density profile, most forms one can choose for n(r), even if integrable, yield potentials ψ(r) that cannot be inverted. The function F can be found parametrically, however, by writing the derivative of n with respect to ψ as the ratio of the radial derivatives of n and ψ. Several nontrivial examples of physical interest are studied. Numerical methods for calculating F are presented, its asymptotic form and integration are investigated, and applications to experiment are discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872375
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  • 85
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    Particle diffusion in the presence of trapping (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2106-2115 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The diffusion of particles in the presence of randomly distributed trapping centres is examined. An analytical approach is developed for three simple models of the trap-release processes. It is shown that the particle motion remains diffusive on the average, but the diffusion coefficient can have large fluctuations. The results of the numerical simulations confirm the main qualitative trends found in the analytical study. Although they are very simple, the models can be useful for the examination of the diffusion in tokamak plasma in the presence of quasi-coherent structures which act as trapping centres. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872376
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  • 86
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    Forbidden regions in ion temperatures for ion acoustic compressive solitary waves for a plasma with two electron temperatures (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2139-2145 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is observed that, there exist certain forbidden regions in ion temperatures, for a compressive solitary wave, which do not have any solitary wave solution. These regions exist for a two- as well as a single-electron temperature plasma. A physical model is proposed to explain this phenomenon on the basis of the energy relation. It is revealed that a one-dimensional single warm ion fluid consists of two distinct energy components. A simple algebraic condition has been derived which expresses the balance between nonlinearity and dispersion for a fully nonlinear solitary wave. It shows that both the nonlinearity and dispersion decrease with increasing ion temperature and that the balance condition is well maintained for the whole spectrum of solitary wave solutions. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872378
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  • 87
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    Vacuum calculations in azimuthally symmetric geometry (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2161-2180 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A robustly accurate and effective method is presented to solve Laplace's equation in general azimuthally symmetric geometry for the magnetic scalar potential in the region surrounding a plasma discharge which may or may not contain external conductors. These conductors can be topologically toroidal or spherical, and may have toroidal gaps in them. The solution is incorporated into the various magnetohydrodynamic stability codes either through the volume integrated perturbed magnetic energy in the vacuum region or through the continuity requirements for the normal component of the perturbed magnetic field and the total perturbed pressure across the unperturbed plasma–vacuum boundary. The method is based upon using Green's second identity and the method of collocation. As useful by-products, the eddy currents and the simulation of Mirnov loop measurements are calculated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872380
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    Dynamics of a high-power aluminum-wire array Z-pinch implosion (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2188-2203 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Annular Al-wire Z-pinch implosions on the Saturn accelerator [D. D. Bloomquist et al., Proceedings, 6th Pulsed Power Conference (Institute of Electrical and Electronics Engineers, New York, 1987), p. 310] that have high azimuthal symmetry exhibit both a strong first and weaker second x-ray burst that correlate with strong and weaker radial compressions, respectively. Measurements suggest that the observed magnetic Rayleigh–Taylor (RT) instability prior to the first compression seeds an m=0 instability observed later. Analyses of axially averaged spectral data imply that, during the first compression, the plasma is composed of a hot core surrounded by a cooler plasma halo. Two-dimensional (2-D) radiation magnetohydrodynamic computer simulations show that a RT instability grows to the classic bubble and spike structure during the course of the implosion. The main radiation pulse begins when the bubble reaches the axis and ends when the spike finishes stagnating on axis and the first compression ends. These simulations agree qualitatively with the measured characteristics of the first x-ray pulse and the overall energetics, and they provide a 2-D view into the plasma hydrodynamics of the implosion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872382
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  • 89
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    Modification of plasma edge fluctuations using electrostatic probes in Keda Tokamak-5C (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2237-2240 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The experiments to characterize the modification of edge fluctuations using electrostatic probes have been performed on Keda Tokamak-5C (KT-5C) [World Survey of Activities in Controlled Fusion Research, Nuclear Fusion Special Supplement (International Atomic Energy Agency, Vienna, 1991), p. 190]. The results show that the externally excited perturbation propagates in the direction of electron directional movement. The observed phenomena are mainly related to the electrons, and can be well explained by the proposed dynamic theory of the ballistic mode. The experimental correlation coefficient and the longitudinal dispersion relation are in good agreement with the proposed ballistic model. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872395
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    Electric-drift generated trajectories and particle acceleration in collisionless magnetic reconnection (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2261-2268 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Adiabatic acceleration of charged particles along magnetic field lines originates from the coupling between the electric drift and longitudinal motion in a nonunidirectional magnetic field. As a result, initially slow particles entering the reconnection site of an X-type magnetic geometry can leave the latter as substantially accelerated jets directed along the magnetic separatrices. The corresponding energy spectrum has a power-law form, with the spectral index depending on the angle between the separatrices. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872555
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  • 91
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    Anomalous electron precipitation near the Earth's auroral zone induced by the wave–particle interaction (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2269-2275 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of a numerical simulation of anomalous electron precipitation in the Earth's auroral zone induced by waves are discussed. In order to study the plasma electron–wave interaction, a two-dimensional quasilinear code has been used. A quasilinear operator models the electron Landau damping of any plasma eigenmodes: kinetic Alfvén waves, whistlers, lower hybrid waves, etc. The distribution function structure was analyzed. The electron current induced by waves, the density, and the plasma energy decay, which stimulates the electron precipitation, have also been investigated. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872390
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  • 92
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    Magnetic electron drift vortex modes with the ion dynamics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 2302-2304 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new dispersion relation for low-frequency magnetic electron drift modes (MEDV) in a nonuniform plasma is derived by incorporating the ion dynamics. It is shown that the ion dynamics introduces new classes of instabilities when the wave frequency either lies between the electron and ion plasmas frequencies or is close to the ion plasma frequency. The modified MEDV modes involving the ion motion can cause nonthermal particle as well as electron heat transports. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872397
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    Evolution of paired luminous rings in capacitive radio-frequency hydrogen discharges (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1179-1181 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temporal and spatial evolution of paired luminous rings is observed in pulsed capacitive radio-frequency (rf) hydrogen discharges. The time-resolved axial profile of the light intensity indicates that the outermost ring pairs near the electrodes start to appear earlier than the inner ones, and that only the left-side (right-side) rings of ring pairs turn on when the rf voltage applied to the left-side (right-side) electrode is positive. The physical mechanism to create the paired rings seems to be similar to that of the standing striations in dc glow discharges. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872357
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    The evolution of plane current–vortex sheets (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1213-1226 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear and nonlinear evolution of the plane current–vortex sheet, with a basic magnetic field given by B0(y)=tanh yêz, and a basic velocity field given by W0(y)=V tanh Ryêz, is examined. The discovery of an ideal instability in a large region of parameter space previously found to be stable is reported. In this paper numerical evidence is presented that this parameter regime is in fact highly unstable, with growth rates exceeding those of the modes existing in the region of parameter space previously found to be unstable. An examination of the perturbation energy balance indicates that enhanced energy transfer from the basic velocity field to the perturbed velocity and magnetic fields is responsible for the enhanced growth rate. This occurs due to processes absent from both the resistive and Kelvin–Helmholtz instabilities. Nonlinearly it is found that magnetic reconnection can occur on an ideal time scale in certain cases. These faster instabilities lead to a more violent cascade of excitation in the streamwise direction, as evidenced by the rapid formation of higher harmonics of the initial disturbance. A nonlinear saturation due to increased correlation of the perturbed velocity and magnetic field occurs for all cases. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872301
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    Velocity–space drag and diffusion in a model, two-dimensional plasma (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1286-1296 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The quasilinear fluctuation integral is calculated for a two-dimensional, unmagnetized plasma (composed of charged rods), and is expressed in terms of Fokker–Planck coefficients. It is found that in two dimensions, the enhanced fluctuations generated by fast electrons lead to anomalously large transport coefficients. In particular, the effect of a small population of fast electrons is only weakly dependent on their density. In three dimensions, the effect of fast electrons is masked by the dominant approximation, but higher-order terms describe processes similar to those in two dimensions, and these terms can become significant for weakly stable plasmas. The differences between two and three dimensions arise from the fact that both emission and damping of plasma waves are retained to lowest order in two dimensions, while the three-dimensional dominant approximation effectively includes only wave emission by test particles. An understanding of the differences between two and three dimensions is crucial to the interpretation of two-dimensional particle simulations. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872304
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  • 96
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    Partial reconnection in the nonlinear internal kink mode (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1326-1329 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the electron pressure gradient in Ohm's law on the nonlinear development of the internal kink mode is investigated. While pressure fluctuations have a destabilizing effect, the average pressure gradient giving rise to diamagnetic flows is stabilizing. If the latter is strong enough, it leads to saturation at finite island size. The relevance of the results for the sawtooth phenomenon in tokamak plasmas is discussed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872308
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  • 97
    Electronic Resource
    Electronic Resource
    A model of ions interacting with neutrals in high electric field and the application to presheath formations (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1308-1315 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of interactions between ions and neutrals in the high electric field is proposed and the exact solution to the Boltzmann equation with the interaction terms is derived. It is shown that the solution produces the known dependence of the ion drift velocity and the mobility on the parameters of the plasma and neutrals in the high electric field. Experimental results on mobilities of N2+ ions in the parent gas are studied by using the formula of the drift velocity obtained in our model. As an application, the presheath formation at the plasma–wall boundary is discussed and a comparison with experimental measurements of sheath potential profiles has been performed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872306
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  • 98
    Electronic Resource
    Electronic Resource
    Submarginal profiles and turbulent transport: An exactly solvable model (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1342-1356 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The possibility that linearly stable ("submarginal") profiles can support turbulent transport in the absence of external noise is considered in the context of a one-dimensional, realizable stochastic model of "almost passive" advection that includes a stability threshold dependent on a critical gradient. The important limits of zero and infinite Kubo number (dimensionless autocorrelation time) are solved analytically. When the stability threshold is linear, it is proven rigorously that, within the context of the model, submarginal profiles do not carry any turbulent flux. A generalization to include a nonlinear stability threshold reminiscent of a subcritical bifurcation supports submarginal profiles. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872496
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  • 99
    Electronic Resource
    Electronic Resource
    Testing the ρ* scaling of thermal transport models: Predicted and measured temperatures in the Tokamak Fusion Test Reactor dimensionless scaling experiments (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1362-1370 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Theoretical predictions of ion and electron thermal diffusivities are tested by comparing calculated and measured temperatures in low (L) mode plasmas from the Tokamak Fusion Test Reactor [D. J. Grove and D. M. Meade, Nucl. Fusion 25, 1167 (1985)] nondimensional scaling experiments. The DIII-D [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] L-mode ρ* scalings, the transport models of Rebut-Lallia-Watkins (RLW), Boucher's modification of RLW, and the Institute for Fusion Studies-Princeton Plasma Physics Laboratory (IFS-PPPL) model for transport due to ion temperature gradient modes are tested. The predictions use the measured densities in order to include the effects of density profile shape variations on the transport models. The uncertainties in the measured and predicted temperatures are discussed. The predictions based on the DIII-D scalings are within the measurement uncertainties. All the theoretical models predict a more favorable ρ* dependence for the ion temperatures than is seen. Preliminary estimates indicate that sheared flow stabilization is important for some discharges, and that inclusion of its effects may bring the predictions of the IFS-PPPL model into agreement with the experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872311
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  • 100
    Electronic Resource
    Electronic Resource
    Effect of the zero spatial harmonic in a slow electromagnetic wave on operation of relativistic backward-wave oscillators (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1402-1412 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A linear theory of resonant backward-wave oscillators (BWOs) that takes into account the zero spatial harmonic is developed. It is shown that, depending on the phase shift, this harmonic can either increase or decrease the starting current of the device. The nonlinear theory shows the same effect of the phase shift on the maximum efficiency of the BWO. The numerical analysis of nonstationary processes has also demonstrated the effect of the phase shift on the range of beam current values in which the BWO operates in a steady-state single-frequency regime. The effect of boundary conditions at the cathode end of the slow-wave structure on the phase shift between harmonics is also analyzed. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872316
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