摘要:

Parametric decay of a lower‐hybrid pump wave into another lower‐hybrid wave and a low‐frequency ion‐sound quasimode (&ohgr;R≊k∥vti) is studied. Such an instability may be excited during high‐power lower‐hybrid heating experiments in tokamak plasmas and may lead to strong modification of the incidentn∥spectrum near the plasma periphery. Such an instability could explain the broadened and downshifted frequency spectrum and phase‐independent heating observed in the Alcator A tokamak experiments. Although the growth rate for this decay increases like &ggr;+&Ggr;2∝E20for powers slightly above threshold (&Ggr;2is the linear damping rate at the lower sideband andE0is the pump electric field), for powers well above threshold (such that &ggr;≳&ohgr;R)&ggr;∝E2/30, and the convective thresholds are rather high. However, for inaccessiblen0∥, the pump wave power is expected to accumulate on the outer surface of the plasma column where the growth rate is large and the convective thresholds are significantly reduced. In such a case the threshold pump power can become quite low and may be exceeded in experiments such as Alcator A.

ISSN:0031-9171    

DOI:10.1063/1.864022

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The effect of trapping on the wave‐breaking amplitude of Langmuir oscillations is discussed in a homogeneous system on the basis of a phenomenological description of trapped particles. The significant effect of trapping is to steepen the wave profile and to enhance the wave‐breaking amplitude of the electric field.

ISSN:0031-9171    

DOI:10.1063/1.864023

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The cubically nonlinear Schro¨dinger equation model of Langmuir turbulence is solved in the weak turbulence limit. Steady‐state power‐law solutions for the energy spectra are found in arbitrary dimensionality. In one spatial dimension, the theory incorrectly predicts that no spectrum evolves in time. In three spatial dimensions, numerical solutions are obtained for the undriven, undamped, initial value problem and for the driven, damped, initial value problem.

ISSN:0031-9171    

DOI:10.1063/1.864024

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Cyclotron resonance heating of bouncing electrons by an obliquely incident wave field is analyzed. Continuous interaction between electrons and wave fields throughout the entire range of electron excursion has been considered in the analysis. The results show that the bouncing motion of electrons serves to alleviate the detuning effect of frequency mismatch and efficient heating can be achieved. The kinetic temperature is found to increase algebraically int2for the fundamental resonance and exponentially intfor the second harmonic heating. Due to the interaction between electrons and the parallel component of the wave electric field, heated electrons tend to focus to the midplane and their excursion amplitudes also become filamented in the steady state.

ISSN:0031-9171    

DOI:10.1063/1.864025

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

In this paper are presented approximate analytic expressions for the emissivity and absorption coefficient of synchrotron radiation of mildly relativistic particles with an arbitrary energy spectrum and pitch angle distribution. From these, an expression for the degree of polarization is derived. The analytic results are compared with numerical results for both thermal and nonthermal (power law) distributions of particles.

ISSN:0031-9171    

DOI:10.1063/1.864026

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The index of refraction and the electron cyclotron absorption coefficient at &ohgr;≊&ohgr;cin the Doppler regime are examined for a plasma in thermal equilibrium. Regimes where the known analytical approximations fail are quantitatively delineated. The exact numerical solution to the dispersion relation is given in the regimes where known analytical theory fails.

ISSN:0031-9171    

DOI:10.1063/1.864027

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A WKB formalism for constructing normal modes of short‐wavelength ideal hydromagnetic, pressure‐driven instabilities (ballooning modes) in general toroidal magnetic containment devices with sheared magnetic fields is developed. No incompressibility approximation is made. A dispersion relation is obtained from the eigenvalues of a fourth‐order system of ordinary differential equations to be solved by integrating along a line of force. Higher‐order calculations are performed to find the amplitude equation and the phase change at a caustic. These conform to typical WKB results. In axisymmetric systems, the ray equations are integrable, and semiclassical quantization leads to a growth rate spectrum consisting of an infinity of discrete eigenvalues, bounded above by an accumulation point. However, each eigenvalue is infinitely degenerate. In the nonaxisymmetric case, the rays are unbounded in a four‐dimensional phase space, and semiclassical quantization breaks down, leading to broadening of the discrete eigenvalues and the accumulation point of the axisymmetric unstable spectrum into continuum bands. Analysis of a model problem indicates that the broadening of the discrete eigenvalues is numerically very small, the dominant effect being broadening of the accumulation point.

ISSN:0031-9171    

DOI:10.1063/1.864028

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Ballooning modes in tandem mirrors with quadrupole vacuum field symmetry are investigated in the limits of zero gyroradius and large aspect ratio. The eigenmode equation derived from the guiding‐center energy principle is reduced to one dimension by the use of an eikonal representation of the cross‐field variation of the perturbation. The eigenvalue problem is solved numerically and the structure of the local dispersion relation examined in order to derive conditions for marginal stability. Applications to the TMX‐U and MFTF‐B tandem‐mirror experiments are presented.

ISSN:0031-9171    

DOI:10.1063/1.864029

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A reduced set of ideal magnetohydrodynamic equations is derived for large‐aspect‐ratio, low‐&bgr; tokamaks that adequately describes the linear and nonlinear evolution of ideal internal kink modes in tokamaks.

ISSN:0031-9171    

DOI:10.1063/1.864030

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A numerical code, which utilizes the stellarator expansion, is developed and tested. It is used to investigate the magnetohydrodynamic stability properties of several stellarator configurations, including Heliotron E, Wendelstein VII‐A, a modular‐coil device, and ATF‐1.

ISSN:0031-9171    

DOI:10.1063/1.864031

出版商:AIP    

年代:1983

数据来源: AIP