摘要:

Results are presented from a detailed study of the formation of strong relativistic shocks from simple waves in a fluid obeying the Synge equation of state for a relativistic particle gas. Subsequent damping is also followed, and the results are compared with those obtained previously for a model radiation‐dominated gas. In this paper, planar flow is considered and self‐gravity of the waves is neglected.

ISSN:0031-9171    

DOI:10.1063/1.865132

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Finite‐amplitude Alfve´n waves can be modeled by a nonlinear wave equation termed the derivative nonlinear Schro¨dinger equation. A computer program has been developed that solves the derivative nonlinear Schro¨dinger equation via the ‘‘split‐step’’ Fourier method. This program has been used to investigate a number of topics in the area of nonlinear Alfve´n waves. When analytic envelope solitons are used as initial conditions, the wave packets propagate without distortion and with the expected speed–amplitude relation. When an arbitrary, amplitude‐modulated wave is used as an initial condition, the results depend strongly on the &bgr; of the plasma and the polarization of the wave. For a left circularly polarized wave in a &bgr;<1 plasma, or a right circularly polarized wave with &bgr;>1, a collapse instability has been observed in which the wave amplitude increases and modulation scale decreases. For other combinations of polarization and value of &bgr;, the wave packet tends to broaden, eliminating the initial modulation.

ISSN:0031-9171    

DOI:10.1063/1.865188

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The nonlinear oscillations of an electron plasma described by the collisionless Vlasov equation are studied using a perturbation technique previously applied by Simon and Rosenbluth [Phys. Fluids19, 1567 (1976)]. It is proved by a characteristic argument that the plasma is globally stable, so that Bogoliuboff’s method of ‘‘secular regularization’’ is applicable. Assuming the plasma is confined in a box, and that only the lowest mode is unstable, it is shown that the ‘‘eigenmode dominance’’ approximation of Simon and Rosenbluth fails to conserve energy, but that energy and momentum conservation can be regained by considering interaction between the discrete and continuum modes. A formula is derived for the amplitude and phase of the saturated nonlinear oscillations. In a subsidiary result, it is shown that nonlinear effects damp the steady‐state oscillations predicted by linearized theory for some stable plasmas.

ISSN:0031-9171    

DOI:10.1063/1.865190

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The Rosenbluth form for the collision operator for a weakly relativistic plasma is derived. The formalism adopted by Antonsen and Chu can then be used to calculate the efficiency of current drive by fast waves in a relativistic plasma. Accurate numerical results and analytic asymptotic limits for the efficiencies are given.

ISSN:0031-9171    

DOI:10.1063/1.865191

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

The combined effects of the dc electric field and electron‐cyclotron wave absorption in tokamak plasmas are investigated. The case of the ordinary mode for nearly normal propagation from the low magnetic field side is studied by a two‐dimensional Fokker–Planck code. It is found that the small fraction of the wave energy that goes into the superthermal electrons enhances the effect of the continuous pushing of the tokamak electric field.

ISSN:0031-9171    

DOI:10.1063/1.865192

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Absorption caused by relativistic broadening of quasiperpendicular incident waves within the second cyclotron harmonic layer is investigated in an inhomogeneous electron plasma. The resonance region is treated by a boundary layer analysis, and field equations valid in this region are derived by solving the rescaled (with respect to the parameter &eegr; which is the ratio of the thermal speed and the speed of light) linearized relativistic Vlasov equation. The geometrical optics solutions valid in the nonresonant region are evaluated near the resonance, and they are connected to the asymptotic forms of the inner solutions. The energy conservation theorems appropriate for this problem allow the evaluation of fractional transmitted and reflected energy, and thus distinguish between the energy mode converted to the quasielectrostatic (relativistic Bernstein) mode and that absorbed by the plasma (which does not exist for the purely perpendicular propagation and nonrelativistic case). Numerical methods are developed which enable one to handle the computation of the excessively stiff differential equations in the high‐field side. The three fundamental scattering problems are then evaluated numerically for various values of electron density and the product of electron temperature and scale length for the variation of the magnetic field for the case of perpendicular propagation. It is found that, unlike the mode coupling, the transmission of the X mode is not affected by the relativistic corrections. In the case of high‐field side incidence, the reflection is still zero as predicted in the nonrelativistic approach. However, in contrast to the zero absorption in the nonrelativistic case, there is significant absorption caused by relativistic broadening, particularly in the case of low‐field side incidence.

ISSN:0031-9171    

DOI:10.1063/1.865173

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

In a previous article, the wave equation for electromagnetic and electrostatic waves propagating in a weakly inhomogeneous plasma was studied assuming an ordinary differential equation of the Laplace type. An algorithm was developed, based on the contour integral formalism, that gives a prescription for calculating the connection formulas between the set of fast and slow propagating waves. Physical problems connected to the evanescent solutions were not treated, however, so the complete set of solutions was not obtained. In this paper, the method is extended to include both propagating and nonpropagating waves so that a complete set of solutions is obtained, permitting the construction of the Green function and the inclusion of localized sources or sinks.

ISSN:0031-9171    

DOI:10.1063/1.865175

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

An unstable, highly intermittent state of turbulence is observed to evolve from a quiescent homogeneous plasma that is linearly stable. This intermittent state, which consists of isolated phase space density holes, produces a pronounced non‐Gaussian distribution of fluctuation amplitudes. The skewness becomes increasingly more negative with time. The plasma is nonlinearly unstable because the holes grow in amplitude by accelerating to regions of higher average phase space density. The instability can be interpreted as a collection of colliding, growing holes and, in its early stages, is consistent with theoretical predictions for the clump instability. A series of runs with a single isolated hole indicates that an isolated hole grows foranyfinite electron‐ion drift velocity. The isolated hole growth rate is consistent with theoretical predictions. The implications of the instability to laboratory and space plasma are discussed.

ISSN:0031-9171    

DOI:10.1063/1.865176

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

Earlier work on the mode conversion theory by Fuchs, Ko, and Bers is detailed and expanded upon, and its relation to energy conservation is discussed. Given a local dispersion relation,D(&ohgr;; k, z)=0, describing stable waves excited at an externally imposed frequency &ohgr;, a pairwise mode‐coupling event embedded therein is extracted by expandingD(k, z) around a contourk=kc(z) given by ∂D/∂k=0. The branch points ofD(k, z)=0 are the turning points of a second‐order differential‐equation representation. In obtaining the fraction of mode‐converted energy, the connection formula and conservation of energy must be used together. Also, proper attention must be given to distinguish cases for which the coupling disappears or persists upon confluence of the branches, a property which is shown to depend on the forward (vgvph>0) or backward (vgvph<0) nature of the waves. Examples occurring in ion‐cyclotron and lower‐hybrid heating are presented, illustrating the use of the theory.

ISSN:0031-9171    

DOI:10.1063/1.865178

出版商:AIP    

年代:1985

数据来源: AIP

摘要:

A series of fluid simulations are reported on strong Langmuir turbulence in two dimensions in the presence of a magnetic field. Starting with a group of Langmuir waves such as would be generated by an electron beam, the strong turbulence is initially one‐dimensional, forming planar solitons. With no transverse wavenumber spread in the initial waves (&Dgr;k⊥=0), the magnetic field leads to more pancake‐shaped solitons by reducingk@B|⊥(the shortest unstable mode), but has little effect on the collapse. For an initial wave packet, ifk*⊥<&Dgr;k⊥, the transverse collapse does not occur.

ISSN:0031-9171    

DOI:10.1063/1.865179

出版商:AIP    

年代:1985

数据来源: AIP