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  • 1
    Electronic Resource
    Electronic Resource
    Detection of S2F10 produced by a single-spark discharge in SF6 (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 2103-2105 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improvement in detection sensitivity of S2F10 in SF6 down to concentrations below 10 parts per billion, using a cryogenic enrichment-gas chromatography technique, has permitted the detection of S2F10 produced by a single-spark discharge in SF6. The spark yield of S2F10 was found to fall in the range of yields found in earlier work on more highly decomposed SF6. Based on preliminary data the spark discharge may provide a suitable and reproducible reference source of S2F10.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354731
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  • 2
    Electronic Resource
    Electronic Resource
    Measurement of electrical avalanches and optical radiation near solid insulators in high pressure (up to 0.3 MPa) nitrogen gas (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 2877-2884 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron and ion avalanches have been recorded near a variety of insulators (plexiglas, teflon, high-density polyethylene, low-density polyethylene, polypropylene, delrin, polyvinyl chloride, and nylon) in nitrogen gas at pressures of 0.1, 0.2, and 0.3 MPa. With the exception of nylon, suppression of avalanches has been observed in the presence of insulators. In addition to electron and ion avalanches, simultaneous measurement of optical radiation associated with an electron avalanche was successfully carried out. Qualitative explanations have been provided for the suppression of avalanches near most insulators and an anomalous growth of avalanches near nylon insulators. Photoemission from nylon surfaces appears to be responsible for the enhanced growth of avalanches near nylon insulators. More precise measurements of optical radiation are needed to better understand the electron-photon interactions near a solid insulator in a gaseous dielectric medium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348596
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  • 3
    Electronic Resource
    Electronic Resource
    Avalanches near a solid insulator in nitrogen gas at atmospheric pressure (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1095-1102 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pulsed Townsend (PT) technique was used to record the growth of avalanches near a solid insulator in nitrogen gas at 0.1 MPa. Several other nonconventional techniques for releasing initiatory electrons at the cathode are discussed. In this paper, experimental results of avalanches initiated by illuminating a fast (0.6-ns) nitrogen laser onto the cathode triple junction are presented. Data were recorded with plexiglas, Teflon, high-density polyethylene, low-density polyethylene, Delrin, etc. Effect of surface condition, variation of the distance between insulator surface and the avalanche initiation region, and the effect of a large number of previous avalanches on the avalanche characteristics at a particular voltage were studied. The Townsend primary ionization coefficient, hereafter referred to as growth coefficient (α), and drift velocity (Ve) were evaluated through the PT technique. Results indicate that the avalanche growth in the vicinity of a solid insulator is less than that in an identical plain gas gap. Existence of a nonuniform field as a result of surface charges on the insulator and/or field modifications due to the avalanche space charge are believed to be responsible for this behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343447
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  • 4
    Electronic Resource
    Electronic Resource
    Explicit analytical solution of the nonlinear Vlasov–Poisson system (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 528-540 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to describe the time evolution of an inhomogeneous collisionless plasma, the nonlinear Vlasov equation is solved perturbatively, using the subdynamics approach and the diagrammatic techniques. The solution is given in terms of a double perturbation series: one with respect to the nonlinearities and the other with respect to the interaction between particles. The infinite sum of interaction terms can be performed exactly due to the property of dynamical factorization. Following the methodology, the exact solution in each order with respect to nonlinearities is computed. For a choice of initial perturbation the first-order exact solution is numerically integrated in order to find the local density excess. The approximate analytical solution is found to be in excellent agreement with exact numerical integration as well as with ab initio numerical simulations. Analytical computation gives a better insight into the problem, and it has the advantage to be simpler, and also accessible, in some range of parameters where it is difficult to find numerical solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870797
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  • 5
    Electronic Resource
    Electronic Resource
    Continuum damping of ideal toroidal Alfvén eigenmodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 381-389 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A perturbation theory based on the two-dimensional (2-D) ballooning transform is systematically developed for ideal toroidal Alfvén eigenmodes (TAEs). A formula, similar to the Fermi golden rule for decaying systems in quantum mechanics, is derived for the continuum damping rate of the TAE; the decay (damping) rate is expressed explicitly in terms of the coupling of the TAE to the continuum spectrum. Numerical results are compared with previous calculations. It is found that in some narrow intervals of the parameter mεˆ, the damping rate varies very rapidly. These regions correspond precisely to the root missing intervals of the numerical solution by Rosenbluth et al. [Phys. Fluids B 4, 2189 (1992)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870839
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  • 6
    Electronic Resource
    Electronic Resource
    Damping of toroidal Alfvén modes in DIII-D (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3277-3287 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The previously developed single-gap kinetic theory for toroidicity-induced Alfvén eigenmodes (TAE) is extended and applied to Doublet III-D [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)] experimental data. It is found that the theory gives reasonable agreement with the data when an appropriate magnetohydrodynamic boundary condition is accounted for. As is shown, this boundary condition is equivalent to an appropriate real frequency shift relative to the continuum gap. The correct eigenfunction near the gap, and thus the correct damping, is obtained by using the gap structure calculated from an equilibrium reconstruction that includes low aspect ratio, noncircularity, and finite beta effects, combined with an experimentally measured frequency. In the considered experimental cases, the damping is well into the nonideal regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870480
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  • 7
    Electronic Resource
    Electronic Resource
    On the robustness of the localized spatiotemporal structures in electron–positron–ion plasmas (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 3264-3269 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that, in an electron–positron plasma with a small fraction of ions, large-amplitude localized spatiotemporal structures (light bullets) can be readily generated and sustained. These light bullets are found to be exceptionally robust: they can emerge from a large variety of initial field distributions and are remarkably stable. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872994
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  • 8
    Electronic Resource
    Electronic Resource
    Velocity shear generated Alfvén waves in electron–positron plasmas (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3545-3555 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear magnetohydrodynamic (MHD) modes in a cold, nonrelativistic electron–positron plasma shear flow are considered. The general set of differential equations, describing the evolution of perturbations in the framework of the nonmodal approach is derived. It is found, that under certain circumstances, the compressional and shear Alfvén perturbations may exhibit large transient growth fueled by the mean kinetic energy of the shear flow. The velocity shear also induces mode coupling, allowing the exchange of energy as well as the possibility of a strong mutual transformation of these modes into each other. The compressional Alfvén mode may extract the energy of the mean flow and transfer it to the shear Alfvén mode via this coupling. The relevance of these new physical effects to provide a better understanding of the laboratory e+e− plasmas is emphasized. It is speculated that the shear-induced effects in the electron–positron plasmas could also help solve some astrophysical puzzles (e.g., the generation of pulsar radio emission). Since most astrophysical plasmas are relativistic, it is shown that the major results of the study remain valid for weakly sheared relativistic plasmas. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871945
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  • 9
    Electronic Resource
    Electronic Resource
    Study of microinstabilities in toroidal plasmas with negative magnetic shear (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3065-3072 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microinstabilities driven by a parallel velocity shear, and a temperature gradient of ions are studied in toroidal plasmas with negative magnetic shear. Both the fluid and the gyrokinetic formulations are investigated. It is found that for a broad range of parameters, the linear growth rates of the modes are lower and the threshold temperature gradient ηicr is higher for plasmas with negative magnetic shear compared to plasmas with positive magnetic shear of equal magnitude. The reduction in the growth rate (with negative shear), although not insignificant, does not seem to be enough to account for the dramatic improvement in the confinement observed experimentally. Other possible physical mechanisms for the improved confinement are discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871654
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  • 10
    Electronic Resource
    Electronic Resource
    Reynolds stress of localized toroidal modes (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 4236-4245 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An investigation of the two-dimensional (2-D) toroidal eigenmode problem reveals the possibility of a new consistent 2-D structure, the dissipative ballooning mode of the second kind (BM-II). In contrast to the conventional ballooning mode, the new mode is poloidally localized at π/2 (or−π/2), and possesses significant radial asymmetry. The radial asymmetry, in turn, allows the dissipative BM-II to generate considerably larger Reynolds stress as compared to the standard slab drift-type modes. It is also shown that a wide class of localized dissipative toroidal modes are likely to be of the dissipative BM-II nature, suggesting that at the tokamak edge, the fluctuation generated Reynolds stress (a possible source of poloidal flow) can be significant. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871048
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