摘要:

A large‐amplitude rf electric field can heat particles at their gyrofrequency and its harmonics despite a significant mismatch between the wave frequency and the gyrofrequency through physical processes analogous to the trapping of particles in large‐amplitude waves. ForeE0k0/m&OHgr;2near unity, the fundamental and the second harmonic resonances may overlap and give rise to stochasticity. The implications for cyclotron heating are discussed.

ISSN:0031-9171    

DOI:10.1063/1.863606

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Fast‐wave propagation in a cylindrical magnetoplasma with periodic boundary conditions approximating those of the Elmo Bumpy Torus (EBT) is analyzed. Significant differences from straight cylinder models are found. For example, for them= −1 poloidal mode and for model EBT‐S (scale) parameters (i.e.,n≲4×1012 cm−3,B= 7–14 kG, and plasma radius ≃15 cm), branches of the dispersion relation occur in bands of frequency separated by frequency intervals where no waves or only short wavelength modes occur, analogous to the stop band zones of free space periodic structures. Another difference is that the number of mode onsets which occur in a given frequency interval is larger than that found for straight cylinder problems. Other results indicate good wave‐energy penetration for eigenmodes in both EBT‐S and EBT‐P (proof of principle). For EBT‐P, withn= 3×1013,B= 22.5 kG, and plasma radius = 17 cm, the wave fields peak strongly in the midplane of the mirror sectors near the minor axis.

ISSN:0031-9171    

DOI:10.1063/1.863607

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The nonlinear evolution of the lower‐hybrid instability is studied analytically for the cross‐field electron drift velocity much larger than the ion thermal velocity (hydrodynamic regime). A nonlinear dispersion relation is derived, in which the frequency as well as growth rate modulation is taken into account, and the ion heating and ion drift motion accompanied by the growth of the instability are renormalized in the ion susceptibility. The dispersion relation determines self‐consistently, in a quasilinear approximation, the time variation of the complex frequency &OHgr;k(t) = &ohgr;k(t)+i&ggr;k(t). Numerical solution of the dispersion relation reveals that the growth rate of the most unstable mode becomes ∼0.1&ggr;0(&ggr;0is the initial growth rate) after several growth periods.

ISSN:0031-9171    

DOI:10.1063/1.863615

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Absolute instability analysis of the coupled modes for stimulated Brillouin scattering for plasmas drifting at velocities rather greater than Mach 0.5 shows that oblique forward scatter is favored rather than backscatter, which is generally stable. For typical laser‐target interaction parameters, a threshold (I&lgr;2) near 2×1015W cm−2&mgr;m2seems reasonable. Light is not lost by re‐emission but only diverted to more oblique incident angles and red‐shifted. In laser‐produced plasmas, reflection near critical density is needed to see the effect. For any condition (including supersonic plasma) absolute instability can only produce red‐shifted light.

ISSN:0031-9171    

DOI:10.1063/1.863616

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Previous work on the absolute instability of Brillouin scatter in drifting plasmas is extended to the case of convective amplification. It is found that, similar to temporal growth rates for the absolute instability, forward oblique scatter has the highest spatial gain, with backscatter near a minimum. To agree with experimental results on outward scattered light, source terms are required which must be many orders of magnitude above thermal. Although in the heavy ion damping regime self‐limiting via ion heating decreases the sensitivity of the final reflectivity to the source strength, there is no evidence of a scattering limit when pump depletion is small (the normal experimental situation).

ISSN:0031-9171    

DOI:10.1063/1.863617

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

The Vlasov stability theory of the two‐stream instability of a scattered relativistic electron beam in a collisional plasma is presented. New analytic results demonstrating the effect of a small but finite scatter (temperature) on the cold beam dispersion relation are given. These provide a basis for a discussion of the continuous transition, with increasing scatter, from the hydrodynamic to kinetic regime of instability. Numerical solutions of the dispersion relation are presented to illustrate some general features observed as well as trends in scaling with the beam parameters.

ISSN:0031-9171    

DOI:10.1063/1.863618

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

It is shown that the electromagnetic finitek∥electron Bernstein mode can be destabilized by the runaway electron distribution which results from the quasilinear action of the magnetized plasma oscillation. This mechanism is shown to yield growth rates of the order of 108 sec−1and is suggested as a mechanism for the enchanced cyclotron harmonic emission in the presence of runaway electrons.

ISSN:0031-9171    

DOI:10.1063/1.863619

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Energy stability theory is employed to determine lower bounds on onset times and global stability bounds for initially isothermal fluid layers subjected to impulsive changes in surface temperature. Various combinations of rigid and free boundary conditions and heating or cooling are considered.

ISSN:0031-9171    

DOI:10.1063/1.863620

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

A perturbation theory describes the exchange of energy between modes with nearly the same linear frequency. A distinction is made between this interaction, which is apparently associated with the initiation of collapse, and the exponentially growing modulation instability.

ISSN:0031-9171    

DOI:10.1063/1.863621

出版商:AIP    

年代:1982

数据来源: AIP

摘要:

Comments on the propagation of acceleration waves of arbitrary shape, which propagate into a gas at rest and is a constant state permeated by a magnetic field, is made. (AIP)

ISSN:0031-9171    

DOI:10.1063/1.863622

出版商:AIP    

年代:1982

数据来源: AIP