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  • 1990-1994  (8)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Dynamo effect and current drive by low-frequency waves (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 515-521 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamo effect due to low-frequency oscillations and its application to the nonresonant current drive are examined. The relevant single particle forces are analyzed and the possibility of the dynamo effect enhancement by thermal effects is investigated. In the collisional two-fluid theory with isotropic pressure the flux-surface averaged parallel dynamo field is found to be solely due to frictional forces. In the collisionless, double-adiabatic approximation the previously reported steady-state collisionless α-effect is shown to be absent. The origin of this discrepancy is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870795
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Lower-hybrid poloidal current drive for fluctuation reduction in a reversed field pinch (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 3517-3519 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Current drive using the lower-hybrid slow wave is shown to be a promising candidate for improving confinement properties of a reversed field pinch. Ray-tracing calculations indicate that the wave will make a few poloidal turns while spiraling radially into a target zone inside the reversal layer. The poloidal antenna wavelength of the lower hybrid wave can be chosen so that efficient parallel current drive will occur mostly in the poloidal direction in this outer region. Three-dimensional resistive magnetohydrodynamic computation demonstrates that an additive poloidal current in this region will reduce the magnetic fluctuations and magnetic stochasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870886
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Plasma flows and fluctuations in intense ion-beam diodes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 758-763 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A possible source of electric field fluctuations in the anode plasma of a magnetically insulated ion diode which have been observed in recent experiments is discussed. It is suggested that these fluctuations are driven by the ion flow which destabilizes an electrostatic mode akin to two-stream instability. Evidence is presented for such a flow and its implications for the electric field polarization and magnitude are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870767
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Space-charge-limited ion flow through an ionizing neutral layer (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 3408-3416 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Space-charge-limited ion flow through an ionizing layer of neutral atoms is studied. The ion flow is between two parallel conducting plates (anode and cathode) with an externally applied voltage between them. An expanding layer of neutral atoms is adjacent to the anode surface, extending a finite distance into the anode–cathode gap. All ions originate either from the anode surface or from the ionization of neutrals; electrons originate only from ionization. Electrons are strongly magnetized by an externally applied, time-independent direct current (dc) magnetic field directed across the ion flow. The ions are unmagnetized, all motion being perpendicular to the conducting plates. Two different models of the anode layer were used to analyze this problem: a multifluid steady-state model and a single fluid time-dependent model. From both models it was found that the anode surface becomes shielded after the ion flux from the ionizing layer becomes larger than the space-charge-limited flux of the reduced gap between the neutral layer and cathode. Comparison was made between the time-dependent model and results from magnetically insulated ion beam diode (MID) experiments. Using an initial areal density of neutral hydrogen and carbon equal to the final observed electron areal density, comparison was made between calculated plasma shielding times and upper bounds on the shielding time observed in experiments. It was found that a layer of neutral hydrogen must contain a minimum of 15% carbon (by number density) to explain the rapid electric field screening observed in experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860634
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Alfvén-ion-cyclotron instability and absence of sawteeth in tokamaks (1990)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 2 (1990), S. 463-466 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Linear stability of the anisotropic energetic ion population, observed in recent experiments at the Joint European Torus [Phys. Rev. Lett. 60, 2148 (1988)], to Alfvén-ion cyclotron wave excitations is analyzed and the saturation mechanism is discussed. In the absence of external heating the anisotropic distribution lifetime is found comparable to the observed delay time in the monster sawtooth crash after the turn-off of the heating. It is suggested that the ponderomotive force of unstable waves is responsible for this delay. Saturated wave fields are found sufficiently large to stabilize the internal kink mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859335
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Fluctuations and low-frequency stability (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 2170-2173 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic fluctuations can cause a modification of time-averaged plasma dynamics. Their presence manifests itself through ponderomotive and magnetization forces. For incompressible transverse plasma motions, the ponderomotive force is mainly responsible for an alteration of the momentum balance while the magnetization causes primarily a modification of Ohm's law. These modifications can substantially affect the low-frequency stability. Specifically, it can be shown that the ponderomotive force of fluctuations driven by velocity-space instabilities can stabilize the ideal internal kink mode in a tokamak and the flute mode in a tandem mirror reactor. Magnetization force of fluctuations can also affect the resistive modes. For the resistive internal kink, thought to be responsible for sawtooth oscillations, this effect can be stabilizing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859631
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Observation of whistler instability in the Phaedrus-B tandem mirror plasma (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2907-2914 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results of whistler instability studies in the Phaedrus-B tandem mirror plasma [Phys. Fluids B 2, 787 (1990)] during electron cyclotron resonance heating (ECH) and ion cyclotron range of frequency (ICRF) heating are compared with theoretical models that predict whistler instability. The experimental results suggest that the whistler instability was caused by "warm'' anisotropic electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860163
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Visible-light spectroscopy of pulsed-power plasmas (invited) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 5127-5131 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the investigations of the plasma behavior in three pulsed-power systems: a magnetically insulated ion diode, and plasma opening switch, and a gas-puffed Z pinch. Recently developed spectroscopic diagnostic techniques allow for measurements with relatively high spectral, temporal, and spatial resolutions. The particle velocity and density distributions within a few tens of microns from the dielectric-anode surface are observed using laser spectroscopy. Fluctuating electric fields in the plasma are inferred from anisotropic Stark broadening. For the plasma opening switch experiment, a novel gaseous plasma source was developed which is mounted inside the high-voltage inner conductor. The properties of this source, together with spectroscopic observations of the electron density and particle velocities of the injected plasma, are described. Emission line intensities during the switch operation are discussed. In the Z-pinch experiment, spectral emission-line profiles of various charge-state ions are studied during the implosion phase. Radial velocity distributions are observed from the line Doppler shifts and widths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143461
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    Paper (German National Licenses)
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