摘要:

The consequences of the presence of suprathermal electrons on the linear stage of modulational instabilities are investigated for a range of parameters appropriate to both laboratory and astrophysical plasmas. Substantial modifications to the growth rate and secondary spectrum are found to occur for instabilities driven by large amplitude Langmuir waves in the dipole limit due to the kinetic effects of the suprathermal electrons. In particular, for reasonable choices of pump amplitude and suprathermal energy density, additional modes become unstable.

ISSN:0031-9171    

DOI:10.1063/1.863390

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Secondary decay of an ion‐acoustic wave is shown to provide an efficient saturation mechanism for stimulated Brillouin scattering in underdense plasma (n<0.5ncr). Phase effects and linear damping of ion waves are included in the analysis. In the weak damping regime, secondary decay dominates linear damping providing efficient saturation of Brillouin scattering. Heavy linear damping of ion waves increases the threshold for secondary decay considerably and very small densities are required to obtain saturation.

ISSN:0031-9171    

DOI:10.1063/1.863391

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The nonlinear evolution of one‐dimensional electron‐ion two‐stream instability in a field‐free plasma is studied both analytically and numerically (computer simulation). The instability is dominated by the fastest growing mode and its harmonics, provided that the initial fluctuation level is sufficiently small. A nonlinear dispersion relation is derived and solved numerically, taking into account; (a) the frequency and growth rate modulation, (b) the electric field up to ‖Ek‖4, and (c) the ’’renormalized’’ particle distribution functions. The model can successfully explain the results of a computer simulation, particularly the presence of an algebraic growth stage following the breakdown of the exponential linear growth, the appearance of harmonics, and the final saturation level. The minimum conductivity found scales as (M/m)0.61wpe, whereM/mis the ion/electron mass ratio.

ISSN:0031-9171    

DOI:10.1063/1.863392

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Modes with azimuthal or poloidal wavenumberm= 1 can appear in the form of internal kinks that are described by the ideal magnetohydrodynamic approximation, or in the form of ’’reconnecting’’ modes that lead to the formation of magnetic islands. An analysis of these modes is developed for collisionless regimes, where the collisional electrical resistivity is negligible and the effects of finite ion inertia and mode‐particle resonance play the most important role.

ISSN:0031-9171    

DOI:10.1063/1.863393

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A simplified nonlinear theory of short wavelength (high‐m) electron temperature‐gradient‐driven tearing modes is presented. Saturation of the linear instability results from nonlinear mode coupling in which energy may cascade to both short and long wavelength modes. The resulting electron thermal conductivity exhibits the density scaling and absolute magnitude observed experimentally.

ISSN:0031-9171    

DOI:10.1063/1.863394

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Low‐frequency waves with high toroidal mode numbers in an axisymmetric toroidal configuration are studied. In particular, the relationship between the periodicity constraints imposed by the geometry, magnetic shear, and the spatial structure of eigenmodes is investigated. By exploiting the radial translational invariance and the poloidal periodicity of the gyro‐kinetic and Maxwell equations, the two‐dimensional problem can be converted into a one‐dimensional one, and the mode structure can be expressed in terms of a single extended poloidal variable. This representation is used in the description of electromagnetic modes with phase velocities larger than the ion thermal velocity and with frequencies below the ion gyro‐frequency. Trapped particle, curvature, and compressional effects are retained. The dispersion equations for drift modes and Alfve´n‐type modes are given in general geometry and simplified solutions are presented in the configuration of a double periodic plane slab.

ISSN:0031-9171    

DOI:10.1063/1.863395

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An investigation of space charge effects associated with moving ions across dc magnetic field lines due to ion cyclotron heating is investigated. Within an electrostatic approximation, an inductive electric field is imposed across a highly inhomogeneous plasma. Two and one‐half dimensional particle simulations examine this problem when electron motion is allowed along but not across the magnetic field. Finitek∥driving structures which allow electron flow, appear to greatly minimize both surface and volume ion space charge effects. Left‐hand electric fields are observed in the plasma which are comparable to the vacuum left‐hand field. Substantial ion heating occurs to the point where ion Larmor radii can be compared to a scale length.

ISSN:0031-9171    

DOI:10.1063/1.863396

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The extent to which nonlinear wave‐particle resonance broadening results in a narrowing of an incident lower‐hybrid wave spectrum is investigated. This narrowing is of concern because it could make control of lower‐hybrid heating difficult. It is shown numerically, however, that relatively uniform spatial power deposition occurs if resonance broadening effects are treated consistently on both the wave spectrum and the particle distribution.

ISSN:0031-9171    

DOI:10.1063/1.863397

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A mode simulation study using the renormalized turbulence theory for the current‐driven ion‐acoustic problem shows the presence of time‐dependent structure in the wavenumber and frequency spectrum.

ISSN:0031-9171    

DOI:10.1063/1.863398

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A toroidal magnetic field configuration in a gravitational field is calculated both from a simple force‐balance and by using magnetic surfaces. The configuration is found to be positionally stable in a star. The vibrational frequency near the equilibrium point is proportional to the hydrostatic frequency of a star multiplied by the ratio (WB/Wm)1/2, whereWBis the magnetic field energy density, andWmis the material pressure at the equilibrium point. It is proposed that this frequency may account for the observed solar spot cycles.

ISSN:0031-9171    

DOI:10.1063/1.863399

出版商:AIP    

年代:1981

数据来源: AIP