摘要:

The collective properties of a plasma, in its interaction with a radiation field, become important when the electron plasma frequency is comparable with, or exceeds, the radiation frequency. The particle interactions must properly be treated quantum mechanically when electron plasma wave phonon energies are of the order of, or greater than, average random electron energies. Both of these conditions may be satisfied for the system of optical or infrared radiation interacting with a dense plasma. Expressions for the high frequency conductivity and opacity are obtained for a dense, fully ionized plasma. It is found that, when the photon energy greatly exceeds the average random energy, and when the electron plasma frequency is much greater than the radiation frequency, then the free‐free contribution to the opacity, ordinarily written without the inclusion of collective effects, is reduced by a factor of the order ofE¯&OHgr;3/ℏ&ohgr;p4, whereE¯is the mean random electron energy in the plasma, &OHgr; is the radiation angular frequency,ℏis Planck's constant, and &ohgr;pis the electron plasma frequency.

ISSN:0031-9171    

DOI:10.1063/1.1711056

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The fundamental solution for the linearized relativistic Vlasov equation with Maxwell's equations is obtained. The unperturbed state is assumed to be spatially homogeneous and time independent, with no electric or magnetic fields. The unperturbed distribution function depends only on the magnitude of relativistic momentum. An examination of the asymptotic behavior of the electric field for large time permits a general description of the solution. The electric field may be expressed as the sum of transverse and longitudinal parts. The transverse part looks like an ordinary electromagnetic wave extremely close to the light cone, and within the light cone it oscillates rapidly with varying frequency and wave number and a local phase velocity greater than the speed of light. Near the origin of the disturbance there is a transition to an ordinary plasma oscillation. In addition to a weak precursor wave, the longitudinal wave propagates outward with a definite speed and behind its wavefront the electric field oscillates with local phase velocity greater than the speed of light. Another ordinary plasma oscillation is left near the origin of the disturbance. The longitudinal speed of propagation goes to zero in the nonrelativistic case and to the speed of light in the extreme relativistic limit. The transverse and longitudinal fields defined according to the Fourier transform modes are not each zero outside the light cone, but their sum is zero. Thus, no signal travels faster than the speed of light. This peculiarity illustrates some unnatural aspects of the separation of a solution into modes of Fourier components.

ISSN:0031-9171    

DOI:10.1063/1.1711057

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The propagation of longitudinal waves in a weakly ionized gas consisting of three species of particles (neutrals, ions, and electrons) is analyzed giving full consideration to the influence of collisions between all three kinds of particles. The calculations are based on Euler's and Poisson's equations. Damping and phase constants for the neutral‐particle wave, the ion wave, and the electron wave are presented for different values of particle densities and for frequencies lower than, or comparable to the plasma frequency of the ions. The main result of the calculations is that in a certain frequency range the damping of the ion wave can be smaller than the damping of the neutral‐particle (sound) wave. This suggests the stimulation of ion waves by means of acoustic transmitters. Such an ion wave would be free of the potentially disturbing neutral‐particle wave at some distance from the source. This method would make it possible to stimulate a purely longitudinal plane wave.

ISSN:0031-9171    

DOI:10.1063/1.1711059

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The general case of a compressible bounded electron plasma is examined. Linearized equations of motion are set up, boundary conditions are established and the possible oscillations that could occur in the spherically bounded plasma examined. Three different modes of oscillations are established; the plasma type of oscillations, the electric type of oscillations, and the magnetic type of oscillations. Dispersion relations for possible modes are obtained.

ISSN:0031-9171    

DOI:10.1063/1.1711060

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The stability of a weakly ionized plasma column in a longitudinal magnetic field containing a small time varying component is investigated, using a macroscopic approach previously developed by the authors for a static field. The time dependence of the field is taken to be linear, and its influence on the column given by the presence of the induced azimuthal electric field. A dispersion relation is derived from the linearized equations of continuity and momentum conservation for the ions and electrons, from which a family of stability boundary curves in theEzvsBplane are found for the case of a helical perturbation in helium. The condition of energy balance of the column including the azimuthal electric field is combined with the dispersion relation to yield a family of stability boundary curves in theE&thgr;vsBplane with gas pressure times column radius as a parameter. These curves indicate regions of stability which are absent in the case of a static magnetic field.

ISSN:0031-9171    

DOI:10.1063/1.1711028

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The electrical behavior of weakly ionized, compressible gases flowing along a solid boundary is studied. Analysis is made for flows wherein the range of electrical effects, such as the sheath thickness, is much greater than the mean free path between the charged and the neutral‐gas particles. The relationships between the surface potential, currents, and the boundary‐layer flow parameters are analyzed.

ISSN:0031-9171    

DOI:10.1063/1.1711029

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Equations have been formulated that govern the interaction between a plane transverse electromagnetic wave and the slightly ionized nonequilibrium gas flowing downstream of a shock wave. Under the assumption that the electromagnetic field is weak, the equations have been linearized and analytical solutions have been obtained. These solutions indicate that significant localized heating of the gas can be accomplished only for narrow ranges of the parameters of the problem. Calculations have been made for the increase in electron density and change in reflection coefficient. The results indicate that very small fields (e.g., 10 mW/cm2) can heat the electrons enough to significantly alter the reflection coefficient.

ISSN:0031-9171    

DOI:10.1063/1.1711030

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

Measurements of absolute intensities of the resonance multiplets of oxygen ions in a typical discharge of the C‐Stellarator are employed to deduce the ion concentrations as a function of time. The analysis of the data is based on an idealized model in which electron temperature and density are uniform both radially and axially. Electron temperatures are found from relative intensities of some of these multiplets, and compared with temperature computed from the electrical conductivity. Mean particle confinement times are deduced from the time behavior of the concentrations of highly ionized oxygen. From these confinement times, and the observed electron density changes, the particle influx rates are obtained. The total power loss by radiation is evaluated for the uniform model. The radiation by oxygen ions, which is explicitly nearly independent of temperature, and the ionization and heating of hydrogen influx, which is nearly proportional to temperature, are found to be the dominating mechanisms of power loss.

ISSN:0031-9171    

DOI:10.1063/1.1711031

出版商:AIP    

年代:1964

数据来源: AIP

摘要:

The electrical discharge in dense plasmas such as those obtained in shock tube experiments is investigated theoretically. Assuming that the positive ion saturation current density is of the order of the positive ion random current density, it is shown that quite high current densities are possible in dense plasmas, without an electron emission at the cathode being required. For instance, current densities up to 1000 A/cm2are possible in argon at a temperature of 15 000°K and a pressure of 1 atm. It is then shown that the positive ion mean free path is in general much larger than the positive space charge sheet near the cathode. Hence the positive ions may be accelerated by the cathode voltage drop. Since their accommodation coefficient is smaller than 1, they keep part of their kinetic energy after neutralization, and they additionally can heat up the plasma in the vicinity of the cathode. This self‐sustained discharge mechanism, which represents a thermal breakdown of the plasma layer near the cathode, reduces the cathode voltage drop and limits the current density to a higher value.

ISSN:0031-9171    

DOI:10.1063/1.1711032

出版商:AIP    

年代:1964

数据来源: AIP

ISSN:0031-9171    

DOI:10.1063/1.1711033

出版商:AIP    

年代:1964

数据来源: AIP