摘要:

The one‐dimensional motion of a gas due to a completely absorbing boundary is examined by means of a four‐moment solution of the nonlinear Boltzmann equation. Definite nonzero values for the density, temperature, and the pressure in the gas at the boundary are computed, and a distinct structure of an expanding Knudsen layer flow is revealed. The gas velocity towards the boundary is found to be weakly supersonic.

ISSN:0031-9171    

DOI:10.1063/1.864655

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A kinetic model for stable, underdense plasma in the presence of a strong electromagnetic pump wave is presented. Ion dynamics are properly treated to account for enhancement in electrostatic fluctuations. Such fluctuations are important even for pump strength below threshold for the oscillating two‐stream and parametric decay instabilities in the underdense region. Thresholds of these instabilities are numerically determined. The results of calculations for the static form factorS(k) electron collision terms, and the absorption coefficient are presented for stable, homogeneous plasmas. For moderate pump values (below instability threshold) enhanced fluctuation levels and increased absorption are found, which have relevance to a variety of experimental situations involving high‐intensity laser, microwave, or radio wave interaction with plasmas.

ISSN:0031-9171    

DOI:10.1063/1.864656

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Considering a high‐frequency electrostatic surface wave that propagates along a plasma cylinder, it is shown that a local change of the axial wavelength of the wave potential may cause solitary variations in the cylinder radius. The magnitudes of these surface displacements are found to depend essentially only on the wavelength perturbation of the high‐frequency wave whereas their propagation velocities are defined by the wave intensity. Previous results, which only included short‐wavelength oscillations, are also generalized.

ISSN:0031-9171    

DOI:10.1063/1.864657

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The interaction of a plasma wave with a long wavelength free‐streaming perturbation is considered in the case of a one‐dimensional electron plasma. A demonstration of this interaction is provided by means of both numerical simulation and analytical theory. The initial distribution function is so chosen as to give rise to an ordinary plasma wave together with a long wavelength disturbance containing a free‐streaming portion. Satellites of the plasma wave are shown to be excited in agreement with earlier work of Morales and Malmberg on the ‘‘linear sideband’’ effect. This result is found to hold when the initial long wavelength disturbance is close to a pure free‐streaming perturbation. In order to have an observable effect in the numerical simulation, it is necessary to increase the density of resonant particles by adding a warm beam to the Maxwellian plasma, in such a way though, as to avoid beam plasma instability. The predictions of analytical theory on the amplitudes of the satellites are compared with the results of numerical simulation and a fair amount of agreement is found both in absolute magnitude and in time evolution.

ISSN:0031-9171    

DOI:10.1063/1.864658

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The systematics of magnetic fluctuations resulting from the nonlinear evolution of high‐&bgr;plong parallel wavelength resistive magnetohydrodynamic modes are studied for circular tokamak plasmas with a free boundary. Large‐amplitude fluctuations cause increased magnetic field stochasticity with increasing &egr;&bgr;p. These fluctuations, when coupled to an anomalous energy loss mechanism, may lead to &bgr;psaturation with respect to total input power.

ISSN:0031-9171    

DOI:10.1063/1.864659

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Model mode‐coupling equations for the resistive drift wave instability are numerically solved for realistic parameters found in tokamak edge plasmas. The Bohm diffusion is found to result if the parallel wavenumber is chosen to maximize the growth rate for a given value of the perpendicular wavenumber. The saturated turbulence energy has a broad frequency spectrum with a large fluctuation level proportional to &kgr;¯ (=&rgr;s/Ln, the normalized inverse scale length of the density gradient) and a wavenumber spectrum of the two‐dimensional Kolmogorov–Kraichnan type, ∼k−3.

ISSN:0031-9171    

DOI:10.1063/1.864660

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An integral representation is derived, within the approximation of geometric optics, for the field of dressed particles in weakly convectively unstable inhomogeneous plasmas characterized by a general non‐Hermitian dielectric tensor. The representation is applied in particular to derive a formula for the velocity space diffusion tensor.

ISSN:0031-9171    

DOI:10.1063/1.864669

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

High toroidal mode number, magnetohydrodynamic perturbations of a plasma confined in an axisymmetric field‐reversed geometry with no toroidal field can be stabilized by the presence of a ring of energetic, large‐orbit ions. Analytical and numerical studies reveal that high‐&bgr; plasma stability against ballooning and interchange modes improves as the ring current profile becomes more peaked. The equations of motion for incompressible mode perturbations in the vicinity of the vortex point are solved analytically to obtain the ballooning stability conditionF>(1+‖&egr;‖)/2, whereFis the fraction of the current density carried by the ring ions and &egr; is the flux surface ellipticity. Higher‐order corrections to the eigenfrequencies due to compressional effects are obtained in the limit of circular flux surfaces. Modeling the ring as an exponential rigid rotor, an iterative procedure is used to obtain optimal values ofEp/Eb, the ratio of the total energy of the confined plasma to the total ring energy. Magnetohydrodynamically stable equilibria are found withEp/Eb≲2.

ISSN:0031-9171    

DOI:10.1063/1.864670

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Particle simulations of drift‐cyclotron‐loss‐cone modes in a tandem‐mirror end cell confirm that sloshing‐ion distributions and the concomitant trapping of low‐energy ions by a depression in the ambipolar potential lead to improved microstablity. The simulations study the influences of neutral‐beam‐injection angle, the magnetic‐mirror ratio, the size of the depression in the ambipolar potential, and warm streaming plasma on both plasma confinement and drift‐cone instability. A simple nonlinear theory of velocity‐space transport predicts wave amplitudes and end‐loss rates at steady state that are reasonably consistent with the simulation results. This study supports both the basic strategy for sloshing‐ion operation of tandem mirrors and corroborates the first measurements of ion‐cyclotron modes in the TMX‐Upgrade experiment at the Lawrence Livermore National Laboratory.

ISSN:0031-9171    

DOI:10.1063/1.864671

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Electron cyclotron resonance heating is one of the most commonly used methods of heating electrons in the plugs and in the thermal barriers of tandem mirrors. The intense coherent electromagnetic waves used for such heating are susceptible to parametric decay into other modes. Significant growth rates are found for the decay of either ordinary or extraordinary waves into two magnetized electron plasma waves. This and related effects may result in electron heating mechanisms rather different than those assumed in linear ray‐tracing calculations. These results may help explain the unusual effects observed during heating of the Phaedrus tandem mirror device. In the general case, these instabilities may be strongly inhibited by density gradients.

ISSN:0031-9171    

DOI:10.1063/1.864672

出版商:AIP    

年代:1984

数据来源: AIP