摘要:

An analysis is presented of the density perturbation produced in a warm plasma by a stratified electromagnetic wave. Filamented wavefields of arbitrary polarization with an intensity distribution which is doubly periodic in the transverse coordinates are considered. The analysis is based on second−order perturbation theory, and comparisons are made with the procedure leading to the well−known ponderomotive potential.

ISSN:0031-9171    

DOI:10.1063/1.860995

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A new general condition for the propagation of slow waves in plasma waveguide systems is derived from the full boundary value problem. Unlike previous calculations, a nonzero collision frequency is retained throughout. The plasmas are assumed to constitute the center conductor of a coaxial waveguide system.

ISSN:0031-9171    

DOI:10.1063/1.860996

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A statistical description of the dynamics of an ensemble of plane waves in nonlinear and strongly dispersive media is derived. A modulational instability, a second sound wave, and a localized group of waves are obtained from the description. The results apply to the dynamics of many optical waves in strongly dispersive dielectric media with the Kerr effect as well as plasma waves for which decays or the wave particle interactions are prohibited.

ISSN:0031-9171    

DOI:10.1063/1.860997

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The mechanism of the trapped−electron instability of a large−amplitude wave is revealed by the following experimental observations: Sideband waves exhibit an initial enhanced damping (examined by the use of linear test excitations) for a distance ∼&lgr;b′the large−wave oscillation length. Beyond this point, the unstable waves grow with a rate linearly proportional to the main−wave electric potential. Measurements show that the instability growth depends on the initial amplitude of the large wave and can persist after this wave field has decayed by tens of decibels. This implication that the driving force of the instability resides in the particles is substantiated by direct measurements of the electron distribution function which, in the presence of a large wave, is found to develop a ’’bump−on−the−tail’’ of sufficient magnitude to account for the observed sideband growth.

ISSN:0031-9171    

DOI:10.1063/1.860998

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

A description is given of theoretical and experimental work on the damping of a second−order electron plasma wave echo due to velocity space diffusion in a low temperature magnetoplasma. Sufficient precision was obtained to verify the theoretically predicted cubic rather than quadratic or quartic dependence of the damping on exciter separation. Compared with the damping predicted for Coulomb collisions in a thermal plasma in an infinite magnetic field, the magnitude of the damping was approximately as predicted, while the velocity dependence of the damping was weaker than predicted. The discrepancy is consistent with the actual non−Maxwellian electron distribution of the plasma. In conjunction with the damping work, echo amplitude saturation was measured as a function of the velocity of the electrons contributing to the echo. Good agreement was obtained with the predictedJ1Bessel function amplitude dependence, as well as a demonstration that saturation did not influence the damping results.

ISSN:0031-9171    

DOI:10.1063/1.860999

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Experimental results of high−vacuum (10−7to 10−6Torr)E−layer trapping experiments on the astron are presented. Both single and multiple pulse experiments are reported. The precessional mode is stabilized with a toroidal field. At sufficiently low pressures (≲5×10−6Torr),Elayers were observed to be stable for up to 200 msec. For greater times, the applied toroidal field had decayed sufficiently so that the layer was unstable to precessions. Axial compression of the layer was observed as it was neutralized by ionization of the background gas. Compressions by a factor of two were observed. For layers whose self−well is the dominant focusing force, this compression agrees with adiabatic theory. A small (≈20%)E−layer loss was observed during the compression. It is felt that this loss arises from scattering in electric field inhomogeneities. The effect of resistive walls on trapping efficiency was studied and it was shown that the efficiency scales with the theoretically calculated energy loss in the resistive walls. Finally, the results of the multiple pulse experiments are presented. Failure to achieve buildup of theElayer is attributed to a combination of losses during compression and poor trapping efficiency on later pulses.

ISSN:0031-9171    

DOI:10.1063/1.861000

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Magnetic field coil measurements are taken in a small theta pinch operated in helium with a capacitor bank energy of 1500 J. The divided pinch coil was connected series antiparallel so that a cusped magnetic field was produced. Plots of current density, magnetic field, and J×B force density are obtained and interpreted via a generalized Ohm’s law. A substantial magnetic field overshoot occurs and is explained in terms of the plasma kinetic energy producing paramagnetic currents via the motional electromotive force. Force density plots of the pinch chamber exhibit a surface of shear in the magnetic force on the plasma which is unusual and suggestive.

ISSN:0031-9171    

DOI:10.1063/1.860981

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Vortex ring parameters such as circulation and translational velocity are estimated from the impulsive motion of a circular disk which generates the vortex ring. A comparison between predicted values of the vortex ring parameters and actually measured values is given.

ISSN:0031-9171    

DOI:10.1063/1.860982

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

The liquid in a partly filled, horizontal, rotating circular cylinder displays at least three different types of periodic, cellular motion. Two of these, which have apparently not heretofore been presented, are described.

ISSN:0031-9171    

DOI:10.1063/1.860983

出版商:AIP    

年代:1975

数据来源: AIP

摘要:

Relativistic modifications of Alfv´en waves are discussed for cases in which magnetic and relativistic terms are comparable. For atmospheric waves there are corrections to velocities, amplitudes, and polarizations. The mass current of the wave itself causes dispersion.

ISSN:0031-9171    

DOI:10.1063/1.860984

出版商:AIP    

年代:1975

数据来源: AIP