摘要:

In cylindrical geometry, as a result of both magnetic shear and density gradient there exist radially trapped lower hybrid decay waves bouncing back and forth in the low density region of the plasma. If this situation persists in toroidal geometry, it could have a severely destabilizing effect on the nonresonant parametric decay of an externally launched lower hybrid heating wave. However, it is shown here that weak toroidicity causes some of these waves to follow ergodic ray trajectories, and hence to be detrapped and to reach their lower hybrid resonance. The fraction of waves which shows ergodic behavior increases as the aspect ratioR0/adecreases. For realistic aspect ratios, i.e.,R0/a≲5, nearly all the rays are ergodic and energy flows toward the resonance. The consequences for lower hybrid wave heating are discussed.

ISSN:0031-9171    

DOI:10.1063/1.862164

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

An exact evaluation of the universal drift instability growth rate in a magnetic field with zero shear is presented. It is based on an asymptotic expansion of the energy equation for large time, in which the change in the kinetic energy of the plasma due to interaction with the wave is obtained from a single particle approach.

ISSN:0031-9171    

DOI:10.1063/1.862165

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The time evolution, due to dissipative processes, of an initial pattern of poloidal and toroidal mass flows in a tokamak is considered. The calculation is applicable to a collisional, low &bgr;, axisymmetric tokamak of arbitrary minor cross section. Time rates of change of poloidal flows which are subsonic but larger than the diamagnetic speed are given according to the magnitude of the flow and the collisionality of the plasma. Over most of parameter space for typical tokamaks, the poloidal rotation is strongly damped by magnetic pumping at the rate (l/qR)2&ngr;ii, wherelis the mean free path,qRis the ’’connection length,’’ and &ngr;iiis the ion‐ion collision frequency. At higher speeds, even stronger damping is effected by electron thermal conduction. The toroidal rotation is determined largely by the conservation of toroidal angular momentum. A heuristic explanation of the damping due to magnetic pumping is given.

ISSN:0031-9171    

DOI:10.1063/1.862166

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Using Grad’s theory of generalized differential equations, the temporal evolution from low to high &bgr; due to ’’adiabatic’’ and nonadiabatic (i.e., neutral beam injection) heating of a cylindrical tokamak plasma with circular cross section and peaked current profiles is calculated analytically. The influence of shaping the initial safety factor profile and the beam deposition profile and the effect of minor radius compression on the equilibrium is analyzed.

ISSN:0031-9171    

DOI:10.1063/1.862167

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The final scyllac experiments are described. These experiments utilized a feedback‐stabilized,l=1,2 high‐beta stellarator configuration and like the previous feedback‐stabilization experiments were carried out in a toroidal sector, rather than a complete torus. The energy confinement time, obtained from excluded flux measurements, agrees with a two‐dimensional calculation of particle end loss from a straight theta pinch. Because simple end loss was dominant, the energy confinement time was independent of whether equilibrium adjustment or feedback stabilization fields were applied. The dynamical characteristics of the toroidal equilibrium were improved by elimination of thel=0 field used previously, as expected from theory. A modal rather than local feedback control algorithm was used. Although feedback clearly decreased them=1 motion of the plasma, the experimental test of modal feedback, which is expected from theory to be superior to local feedback, is considered inconclusive because of the limitations imposed by the sector configuration.

ISSN:0031-9171    

DOI:10.1063/1.862179

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The absorption and transformation of electromagnetic waves in the vicinity of electron cyclotron harmonics is considered. The results of a simple WKB theory and a full wave theory are compared. It is found that for waves perpendicularly incident on a resonant surface (where the wave frequency equals an integer multiple of the electron cyclotron frequency), the full wave treatment is necessary to determine reflection and mode conversion coefficients, whereas, the WKB theory and full wave theory predict the same transmission coefficient. As the angle of incidence is decreased from 90°, the reflection and mode conversion coefficients become unimportant so that the full wave theory and WKB theory agree. The relevance of these processes to the heating of toroidal plasmas with high frequency waves is discussed.

ISSN:0031-9171    

DOI:10.1063/1.862180

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Absorption of magnetosonic cavity modes by excitation of the spatial Alfve´n resonance and by resonant particle absorption (transit time magnetic pumping) are studied and the strengths of the two damping mechanisms compared. For the mode studied, the poloidal mode number is low. This implies that the magnetosonic turning point is close to the Alfve´n resonance. To deal with the resulting differential equation an asymptotic expansion technique is utilized, first using ideal magnetohydrodynamic equations, and, subsequently, with finite ion Larmor radius effects included. The antenna impedance and cavityQare studied as a function of plasma and antenna parameters. It is found that either Alfve´n resonance or resonant particle absorption dominate depending principally on radial mode number.

ISSN:0031-9171    

DOI:10.1063/1.862181

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Radio‐frequency plugging and heating of a magnetized sheet plasma has been studied both experimentally and theoretically. It is confirmed that a sheath resonance related to ion motion occurs at a frequency intermediate between the ion cyclotron frequency and the lower hybrid frequency, and an anti‐resonance occurs at the lower hybrid frequency. The rf electric field in the plasma, which produces a ponderomotive force on the ions, is strongest at the sheath resonance, and is used for the nonadiabatic rf plugging of the magnetized sheet plasma in a mirror field. The ion heating process is explained by Joule heating due to the rf electric field.

ISSN:0031-9171    

DOI:10.1063/1.862182

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

A rapid method is used to find the least‐damped root of the dispersion equation for electrostatic waves in a Maxwellian magnetoplasma, including the effects of field‐aligned drift; the low‐temperature and low‐drift approximations are avoided. Calculations are made of the potential created by an alternating point charge at a frequency less than both the plasma and the electron cyclotron frequencies, neglecting collisions, forced ion motion, and the contributions of higher‐order roots. A comparison of the numerical results with the approximate expressions previously published shows that the latter are inadequate for diagnostic purposes, i.e., for deducing electron density, temperature, and drift velocity from measurements of the potential.

ISSN:0031-9171    

DOI:10.1063/1.862183

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Two elliptically polarized waves in a cold and unmagnetized plasma are found to have self‐precession and frequency shift. For one wave they depend upon the amplitudes and frequencies of both. Due to the presence of the second wave the self‐precession of the first wave increases if its eccentricity is less than that of the former.

ISSN:0031-9171    

DOI:10.1063/1.862184

出版商:AIP    

年代:1978

数据来源: AIP