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  • 1
    Electronic Resource
    Electronic Resource
    Evolution of toroidal Alfvén eigenmode instability in Tokamak Fusion Test Reactor (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 393-404 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear behavior of the toroidal Alfvén eigenmode (TAE) driven unstable by energetic ions in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 1, 1560 (1994)] is studied. The evolution of instabilities can take on several scenarios: a single mode or several modes can be driven unstable at the same time, the spectrum can be steady or pulsating, and there can be negligible or anomalous loss associated with the instability. This paper presents a comparison between experimental results and recently developed nonlinear theory. Many features observed in experiment are compatible with the consequences of the nonlinear theory. Examples include the structure of the saturated pulse that emerges from the onset of instability of a single mode, and the decrease, but persistence, of TAE signals when the applied rf power is reduced or shut off. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872098
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  • 2
    Electronic Resource
    Electronic Resource
    Role of Alfvén instabilities in energetic ion transport : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 1880-1884 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments with plasma heating by waves at the ion cyclotron resonance of a minority species have shown that the heating efficiency degrades above a certain power threshold. It is found that this threshold is due to the destabilization of a branch of shear Alfvén waves, the Energetic Particle Modes, which causes a diffusive loss of fast ions. These modes not only play a fundamental role in the transport of the fast ions, but appear closely related to the formation of giant sawteeth. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873446
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  • 3
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequencies heating and current drive in deuterium–tritium plasmas (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2427-2434 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first experiments utilizing high-power radio waves in the ion cyclotron range of frequencies to heat deuterium–tritium (D–T) plasmas have been completed on the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)]. Results from the initial series of experiments have demonstrated efficient core second harmonic tritium (2ΩT) heating in parameter regimes approaching those anticipated for the International Thermonuclear Experimental Reactor [D. E. Post, Plasma Physics and Controlled Nuclear Fusion Research, Proceedings of the 13th International Conference, Washington, DC, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239]. Observations are consistent with modeling predictions for these plasmas. Efficient electron heating via mode conversion of fast waves to ion Bernstein waves has been observed in D–T, deuterium-deuterium (D–D), and deuterium–helium-4 (D–4He) plasmas with high concentrations of minority helium-3 (3He) (n3He/ne(approximately-greater-than)10%). Mode conversion current drive in D–T plasmas was simulated with experiments conducted in D–3He–4He plasmas. Results show a directed propagation of the mode converted ion Bernstein waves, in correlation with the antenna phasing. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871266
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  • 4
    Electronic Resource
    Electronic Resource
    Ion cyclotron range of frequency experiments in the Tokamak Fusion Test Reactor with fast waves and mode converted ion Bernstein waves (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2006-2012 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recent experiments in the ion cyclotron range of frequencies (ICRF) in the Tokamak Fusion Test Reactor [Fusion Technol. 21, 13 (1992)] are discussed. These experiments include mode conversion heating and current drive, fast wave current drive, and heating of low (L)- mode deuterium–tritium (D–T) plasmas in both the hydrogen minority and second harmonic tritium regimes. In mode conversion heating, a central electron temperature of 10 keV was attained with 3.3 MW of radio-frequency power. In mode conversion current drive experiments, up to 130 kA of current was noninductively driven, on and off axis, and the current profiles were modified. Fast wave current drive experiments have produced 70–80 kA of noninductively driven current. Heating of L-mode deuterium and D–T plasmas by hydrogen minority ICRF has been compared. Finally, heating of L-mode D–T plasmas at the second harmonic of the tritium cyclotron frequency has been demonstrated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871997
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  • 5
    Electronic Resource
    Electronic Resource
    Electron heat transport in a steep temperature gradient (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 741-749 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Temporal and spatial measurements of electron heat transport are made in the University of California Davis AURORA device (J. H. Rogers, Ph.D. dissertation, University of California, Davis, 1987). In AURORA, a microwave pulse heats a region of underdense, collisional, plasma (n/ncr (approximately-less-than)1, where ncr =1.8×1010 cm−3 is the critical density, Te0 ≈0.15 eV, and the electron scattering mean free path λ⊥(approximately-greater-than)2 cm). In this region, strong thermal heating (Tc (approximately-less-than)0.7 eV) as well as suprathermal heating (Th≈3 eV) is observed. The strong heating results in a steep temperature gradient that violates the approximations of classical heat diffusion theory (LT/λ⊥(approximately-greater-than)3 for thermal electrons, where LT=Tc(∂Tc/∂z)−1 is the cold electron temperature scale length. The time evolution of the electron temperature profile is measured using Langmuir probes. The measured relaxation of the temperature gradient after the microwave pulse is compared to calculations using the Fokker–Planck International code [Phys. Rev. Lett. 49, 1936 (1982)] and the multigroup, flux-limited, target design code lasnex [Comm. Plasma Phys. 2, 51 (1975)]. The electron distribution function at the end of the microwave pulse is used as initial conditions for both codes. The Fokker–Planck calculations are found to agree very well with the measurements. However, the flux-limited diffusion calculations do not agree with the measurements for any value of the flux limiter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859139
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  • 6
    Electronic Resource
    Electronic Resource
    Beat wave excitation of electron plasma waves in a toroidal magnetized plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1920-1926 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrostatic waves are driven in a toroidal plasma by counterpropagating microwave beams with a difference in frequency approximately equal to the electron plasma frequency. Energetic electrons are detected when the phase velocity of the electrostatic waves are 3ve〈 vph 〈 7ve, where ve is the electron thermal velocity. Experiments are performed in the Davis Diverted Torus (DDT) [Bull. Am. Phys. Soc. 33, 2049 (1988)] operating in a high repetition rate (15 Hz), low-density (7×107–2×109 cm−3) mode with only a toroidal magnetic field (∼110 G). The microwaves are triggered 30 μsec after the pulsed discharge ends. At this time the energetic electrons have left the system and the velocity distribution is Maxwellian (Te ∼ 1 eV). The microwaves have tunable frequencies over the range 8.5–9.5 GHz, and peak powers ∼180 kW (400 nsec). Bounded plasma modes are excited when the electron cyclotron frequency is larger than the electron plasma frequency. Direct measurements of the wave vector have been made with a double probe antenna, from which the dispersion relation of the electrostatic wave can be obtained. The electron distribution is measured with an electrostatic energy analyzer. The electron velocity distribution function is found to be constant over an interval that extends well beyond the phase velocity of the wave.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860044
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  • 7
    Electronic Resource
    Electronic Resource
    A simple fast pulse gas valve using a dynamic pressure differential as the primary closing mechanism (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1410-1413 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we describe a simple fast pulse gas valve developed for use in a plasma discharge experiment. The valve delivers 1017–1019 molecules per pulse varied by changing the voltage on the electromagnetic driver power supply. Valve pulse widths are observed to be less than 300 μs full width at half maximum with a rise time of less than 100 μs resulting in a maximum gas flow rate of ∼1022 molecules per second. An optical transmission technique was used to determine the mechanical opening and closing characteristics of the valve piston. A fast ionization gauge (FIG) was used for diagnosis of the temporal character of the gas pulse while the total gas throughput was determined by measuring the change in pressure per pulse in a small test chamber with a convectron tube gauge. Calibration of the FIG was accomplished by comparing the net change in pressure in a large chamber as measured by the FIG to the net change in pressure in a small test chamber as measured by the convectron tube gauge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144053
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  • 8
    Electronic Resource
    Electronic Resource
    Application of microwave reflectometry to the measurement of fast magnetosonic waves in the Tokamak Fusion Test Reactor : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 450-453 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The application of microwave reflectometry to the study of fast magnetosonic waves in the Tokamak Fusion Test Reactor (TFTR) is investigated. Assuming the validity of geometric optics for reflectometer measurements, it is shown that linearity to the fast wave amplitude is restricted to very small density fluctuation levels (ñ/n〈10−3). Beyond this level, both phase and amplitude ambiguities occur that makes interpretation difficult. Measurements of 30 MHz fast magnetosonic waves in the core of TFTR plasmas are presented. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147604
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  • 9
    Electronic Resource
    Electronic Resource
    Validating cylindrical Langmuir probe techniques (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 31-36 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Several methods for estimating the plasma potential and density using cylindrical Langmuir probes are compared to the self-consistent solutions of the Vlasov–Poisson equations calculated by Laframboise (J. G. Laframboise, Ph. D. dissertation, University of Toronto, 1966). Measurements are made during the decay of a magnetic-field-free plasma in which the mean-free path of the electron is shorter than the dimensions of the vacuum vessel (the electrons, therefore, have a Maxwellian velocity distribution). The measurements are made in a parameter range in which exact analytical solutions do not exist for the ion and electron saturation currents, 0.5≤R/λDe≤5, where R is the probe radius and λDe is the electron Debye length (kTe/4πne2)1/2. An iterative procedure is used to fit the data at probe voltages both above and below the plasma potential while constraining the curves to be continuous at the plasma potential. The measured curves could be represented extremely well by the numerical results. It is therefore assumed that the plasma parameters used to fit the numerical results to the measurements are correct. The systematic errors which result from using several analysis techniques which assume R/λDe(very-much-less-than)1 are also presented, and it is shown that empirical corrections to these errors can be described which compensate for the finite probe radius.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142743
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  • 10
    Electronic Resource
    Electronic Resource
    Calretinin and calbindin in the retina of the developing chick (1991)
    Springer
    Cell & tissue research 264 (1991), S. 197-208 
    Details
    ISSN: 1432-0878
    Keywords: Retina ; Calcium-binding proteins ; Development, ontogenetic ; Caretinin ; Calbindin-D28k ; Neurons ; Cell death ; Synaptogenesis ; Chick
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Calretinin and calbindin-D28k are two calcium-binding proteins that are present in largely different sets of nerve cells in the central nervous system. Their appearance during development of the chick retina was studied by immunohistochemistry and Western blots. The patterns are mature one day before hatching. Each cell type acquires its characteristic calcium-binding protein several days after its differentiation has started, but in most cases before morphological maturation is complete. There is also an early phase of calbindin immunoreactivity in many immature amacrine cells, and of calretinin immunoreactivity in the presumptive photoreceptor layer, suggesting that these proteins may have distinct functions in differentiating cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00313956
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