摘要:

The nonlinear effects resulting from the propagation of a moderately strong electromagnetic wave in a fully ionized plasma are investigated; a detailed study of the case, when the incident frequency is in the vicinity of the plasma frequency, has been made. The nonlinear contributions to the absorption of the wave and to the reflected components from a plasma‐free space interface, have also been obtained. It is shown, in contrast with earlier work, that under some conditions the nonlinear effects canincreasethe absorption. The generation of harmonic components in the current density and the reflected wave has also been studied.

ISSN:0031-9171    

DOI:10.1063/1.1691806

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The nonlinear response of a Vlasov plasma has been calculated numerically for several externally applied electric field configurations. In the presence of a standing wave of frequency&ohgr;0≳ &ohgr;pe, the energy of the particle distribution and the envelope of the particle electric field were found to oscillate slowly with approximately the period of the trapped particles. Analogous spatial oscillations have been reported by Malmberg and Wharton. Bernstein, Greene, and Kruskal equilibria were calculated for a constant, sinusoidal inhomogeneity in the background ion charge density and found to be numerically stable against small perturbations. Landau‐damping rates for the perturbations are compared with the calculations of Jackson and Raether. In the presence of a slowly varying(&ohgr;0≪ &ohgr;pe)inhomogeneous background (simulating an ion acoustic wave) the electrons were found to obey a locally isothermal equation of state to within a few percent for the times that could be calculated. The response of an initially uniform plasma to a suddenly applied external field was also calculated.

ISSN:0031-9171    

DOI:10.1063/1.1691807

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

In the collisionless case, nonlinear effects considerably reduce Landau damping after times of the order of the period of oscillations of trapped electrons. A perturbation analysis of the nonlinear Vlasov equation, modified by the addition of a simplified Fokker‐Planck collision term, is carried out following Montgomery's expansion technique. The modified Landau poles for Maxwellian plasmas are determined. The first‐order number density and the second‐order spatially homogeneous distribution function are evaluated. A numerical solution of the same equation, using the method of velocity Fourier transforms, is also presented and the results of the two methods are compared. Several values of the collision parameter &bgr;, wavelength &lgr;, and initial amplitude &egr; are considered, showing the competing effects of nonlinearities and collisions on the formation of a plateau in the spatially homogeneous distribution function. Values of &bgr; which prevent the formation of the plateau and maintain Landau damping close to the value prescribed by the linear theory are determined.

ISSN:0031-9171    

DOI:10.1063/1.1691808

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Ion acoustic waves have been magnetically excited and optically detected in a highly ionized argon plasma in the presence of a longitudinal magnetic field. The dispersion of the waves has been studied as a function of the exciting frequency between 187 kHz and 352 kHz and with the confining static magnetic field in the range 800‐2200 G. A dispersion relation is derived which includes the combined effects of ion drift velocity, ion thermal motion, damping, axial magnetic field, and finite beam geometry as adjustable parameters. Dispersion curves are presented which compare the experimental data to the dispersion relation, the parameters being evaluated by a least‐squares fit. The agreement is good.

ISSN:0031-9171    

DOI:10.1063/1.1691809

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The quasilinear stabilization of the garden‐hose instability is discussed from a macroscopic point of view with closure in the fluid model obtained by neglecting the effects of heat flow. In order to keep the problem well‐posed mathematically finite Larmor radius corrections to the conventional growth rate are retained, which leads to a natural cutoff in the growth rate for sufficiently large wavenumber.

ISSN:0031-9171    

DOI:10.1063/1.1691810

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Plasma confinement in the toroidal octopole device is described. The octopole field is produced by four current‐carrying rings which are held in place by supporting rods. A toroidal field may also be applied. The plasma is injected from a coaxial gun. The density is variable from108cm−3to 1011cm−3and the ion and electron temperature is approximately 100 and 6 eV, respectively. Measurements are performed by neutral and ion analyzers and by electrostatic and magnetic probes. The ion confinement time depends on the plasma density. At densities higher than1011cm−3, the high‐energy ions are lost in tens of microseconds by charge exchange interactions with the gas released by plasma bombardment near the injection window. At plasma densities below1011cm−3the ion confinement time is several hundreds of microseconds at 100‐eV ion energies. The decay is consistent with the loss to the supporting rods. The decay rate is at least an order of magnitude less than predicted from the Bohm diffusion coefficient.

ISSN:0031-9171    

DOI:10.1063/1.1691811

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

In a Penning discharge in a magnetic mirror field with an axial mirror ratioBmax/Bmin = 40, a burning voltage as high as 20 kV with a current of a few amps is observed. Normally, the gas is hydrogen in the pressure range10−4‐10−3Torr. The classical mean free path is longer than or comparable to the dimensions of the device. From calorimetric measurements on the cathodes, the plasma density and ion energy in the cathode regions are estimated to a few times1010cm−3and a few kiloelectron volts, respectively. Magnetic loop measurements in the anode region indicate a plasma energy density in that region of1012‐1013eV/cm3. Neutral particles, emitted perpendicular to the magnetic field, with energies exceeding 4 keV, are observed with a scintillator. Measurements on a split anode show oscillations in the frequency range 3‐20 kHz. The aim of the experiment is to investigate the potential distribution in this type of low‐density plasma, in particular the electric field component parallel to the magnetic field, and to determine typical energies of the plasma particles.

ISSN:0031-9171    

DOI:10.1063/1.1691812

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Measurements of the period and logarithmic decrement of oscillating disks indicate that the inertial part of the corner parameter is zero. This result is used to correct the pile of disks measurements of the normal fluid density of liquid helium II.

ISSN:0031-9171    

DOI:10.1063/1.1691813

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The rate of heat transfer to fine wire probes was used to measure the flow nonuniformity in a shock tube. Some systematic differences were observed between the measured quantities and those calculated using the theory of Mirels.

ISSN:0031-9171    

DOI:10.1063/1.1691814

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A method is described for producing explosive‐driven, spherical, imploding shock waves. The implosion waves provide a means for conducting physical experiments at extreme pressures and temperatures in the laboratory, in a reusable facility.

ISSN:0031-9171    

DOI:10.1063/1.1691815

出版商:AIP    

年代:1968

数据来源: AIP