摘要:

The problem of separation of the shock wave and current sheet in magnetically driven shock tubes is examined. Experiments were performed in cold, unmagnetized hydrogen in a large, fast inverse pinch shock tube in which the simple ``skin‐depth criterion'' for obtaining separation was satisfied. Direct measurements of the shock by piezoelectric gauges, and the current sheet by magnetic probes, show that separation nevertheless did not occur. Although the shock wave was located at the very front of the current layer, the layer became much thicker at low pressures than predicted by the skin depth theory. Various mechanisms involved in the emergence of a shock from a current layer, and in the thickening of this layer, are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1762043

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

A plasma bearing a large current is shown to permit three classes of expansions in the direction of the current path: (1) normal rarefaction, (2) discontinuous or shock rarefaction, (3) extension or waveless rarefaction. The general problems is analyzed and application is made to a hydrogen plasma.

ISSN:0031-9171    

DOI:10.1063/1.1762044

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effect of a rectilinear current on Alfve´n waves in a bounded medium is investigated. An infinite spectrum of frequencies corresponds to each Alfve´n frequency obtained without the current. Therefore theI = 0case is considered as degenerate since eigenfrequencies tend to the Alfve´n frequency in this limit. A radial component of the disturbed field will always be present, even though none need be present for the current‐free case. This component is a discontinuous function of the current (discontinuous at zero). A formula connecting the radial and azimuthal components of the field is obtained. This formula carries through when theI →0limit is taken. For theI = 0case the azimuthal and radial fields are completely unconnected, hence the discontinuity. In particular the azimuthal component of the magnetic field will vanish on the boundaries for all finite currents and in theI → 0limit, even though this is not true of theI = 0case. The boundary conditions on the azimuthal component of the field are therefore seen to be discontinuous.

ISSN:0031-9171    

DOI:10.1063/1.1762045

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

When a positive column is submitted to a transverse magnetic field the Lorentz force compresses the electron gas towards one side of the vessel containing the plasma. This phenomenon is analysed in planar geometry at low gas pressure. The ion mean free path is assumed to be at least several times the discharge width. The behavior of the ionic gas is treated using a fluid type version of free fall theory. Plasma density and potential profiles are obtained for various magnetic field strengths. The potential difference between the two insulating discharge walls, or the Hall voltage, is derived and found to be a nonlinear function of the magnetic field. The solution of the free‐fall problem permits to formulate the five equations of balance of a magnetized plasma slab. These are used to determine the electron temperature and the longitudinal electric field of the positive column.

ISSN:0031-9171    

DOI:10.1063/1.1762046

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The effect of resonant charge exchange collisions between an initially monoenergetic unipolar ion stream and a uniform neutral background gas is investigated by postulating a simplified collision mechanism. First‐order approximation to the velocity distribution function for distances small compared to the mean free path and an asymptotic distribution function for large distances are obtained; both are found to be highly anisotropic. The results are valid if the ion energy gained between subsequent collisions is large compared with the thermal energy of the neutral gas. Errors introduced by the physical assumptions are discussed.

ISSN:0031-9171    

DOI:10.1063/1.1762047

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

An equation which describes statistically the motion of charged particles in response to fluctuating electric and magnetic fields is derived. The particles are assumed to be moving in a mirror‐type magnetic geometry. In addition to a static magnetic field there are small superposed fields fluctuating randomly on such a time scale that the first and second adiabatic invariants,MandJ, are conserved, but the third or flux invariant &phgr; is violated. By using second adiabatic theory a two dimensional diffusion equation is obtained valid on a much longer time scale than that of the fluctuations. Elements of the diffusion tensor are time—space correlations of fluctuation‐induced perturbations in the guiding center drifts. These drift perturbations are systematically derived and shown to reduce simply in various special cases.

ISSN:0031-9171    

DOI:10.1063/1.1762048

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

Previously derived formal expressions for the mean‐square deflection of a beam of energetic test particles from a spatially uniform plasma are evaluated numerically. The plasma electrons are assumed to be drifting relative to the ions with a velocity which ranges between zero and the critical drift velocity for the onset of the ion sound wave instability. Though the scattering angle diverges at the stability boundary, one must be able to make the drift velocity prohibitively close to the critical drift velocity (to within a small fraction of a percent of it) to see a marked enhancement. In no case was the scattering enhanced over the thermal value by as much as a factor of 10.

ISSN:0031-9171    

DOI:10.1063/1.1762049

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The combined effect of the anisotropic and frequency‐dependent character of the polarizability of a magnetoplasma which gives rise to a very peculiar and energy‐dependent angular distribution of the radiation emitted by a test ion, is considered.

ISSN:0031-9171    

DOI:10.1063/1.1762050

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The absorption and emission properties of a hot bounded plasma can be greatly influenced by collective behavior in the plasma. A homogeneous slab model of a collisionless plasma is used in a theoretical study of these collective effects. Peaks in the absorptivity occur at the resonance frequencies of longitudinal standing waves in the plasma. Power can be absorbed from an incident electromagnetic wave by Landau damping of the plasma waves which it couples to. Radiation is emitted from a collisionless bounded plasma because plasma waves excited in the wakes of fast electrons are partially converted to electromagnetic waves at the plasma boundaries. The radiation has peaks at the same frequencies as the absorption because of the collective reinforcement of the plasma waves at their resonance frequencies. In thermal equilibrium the collisionless absorption and emission obey Kirchhoff's law. The emission may be enhanced if many nonthermal electrons are present.

ISSN:0031-9171    

DOI:10.1063/1.1762051

出版商:AIP    

年代:1967

数据来源: AIP

摘要:

The nonlinear interaction of two warm interpenetrating electron and ion streams is treated by investigating the traveling wave solutions to the two fluid macroscopic plasma equations. These equations are reduced to the form of a nonlinear differential equation with an additional small nonlinear term. Application of the perturbation procedure, described previous by [J.P. Freidberg, Phys. Fluids 10, 171 (1967)], leads to (1) conditions on the maximum amplitudes for which traveling wave solutions exist and (2) a nonlinear amplitude dependent dispersion relation. An examination of this dispersion relation indicates that below a certain critical temperature there is a range of wavenumbers where the two stream instability may level off before the amplitude reaches the maximum amplitude for existence of traveling wave solutions. This range of wavenumbers decreases with increasing temperture and therefore is largest when the temperature is zero.

ISSN:0031-9171    

DOI:10.1063/1.1762052

出版商:AIP    

年代:1967

数据来源: AIP