摘要:

An electron cloud surrounding a toroidal satellite and held in place by a strong magnetic field(B2/2&mgr;0≫12&egr;0E2≈ neeV ≫ nekTe)has been suggested as a means of raising the satellite to a large positive potential. Symmetry insures that theE × Bdrift of the electrons satisfies the continuity equation, and the problem of steady equilibrium is reduced to finding electron density distributions such thatE·B = 0wherever electrons are present; in other regionsne = 0. It is shown that the development of a “hole” in the electron cloud at large distances from the axis of symmetry is likely. Representative two‐dimensional models are analyzed. At the edge of the electron cloud the appropriate boundary condition is closely related to the Kutta‐Joukowski condition of elementary aerodynamics.

ISSN:0031-9171    

DOI:10.1063/1.1691998

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The electrical effects of a charged sphere immersed in weakly ionized gas of infinite extent are analyzed on the basis of kinetic theory. Approximate solutions are obtained by the application of a moment method in which velocity space is split on the basis of exact orbit calculation, self‐consistent with the field. The theory is shown to reproduce both the collisionless and the continuum results in the appropriate limits. Detailed analysis is performed asymptotically for small Debye length but arbitrary mean free path. For quantitative calculations a completely absorbing probe surface at a highly negative potential is chosen. Criteria for the collisionless or collision‐dominated sheath are obtained explicitly. The voltage‐current characteristics are presented in a form useful for direct prediction of electron number density in terms of measured voltage and current, provided the mean free path is known. If the mean free path is only estimated, the results can be used directly to check self‐consistency of that estimate.

ISSN:0031-9171    

DOI:10.1063/1.1691999

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The flow of secondary electrons, produced by ionization when an electron beam traverses a gas, is retarded by electrostatic fields and their density is higher than has previously been assumed. An experiment indicates that low energy electrons could have important effects on an electron‐beam density and temperature probe and that further research is needed.

ISSN:0031-9171    

DOI:10.1063/1.1692000

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Calculations have been made of the steady‐state ion velocity distribution functions for a partially ionized gas which is not in thermal equilibrium. The electron and neutral gases are assumed to have Maxwellian distributions such that Te≤ Tn. The effects of ion‐electron and ion‐ion Coulomb collisions are represented by appropriate Fokker‐Planck terms, while the ion‐neutral collision term has been derived for resonance charge exchange. It is found for the case of atomic oxygen ions that little distortion of the ion distribution from Maxwellian occurs for ranges of electron and neutral temperatures and particle number densities of geophysical interest. Further, even if ion‐ion collisions are neglected, a nearly Maxwellian distribution results for steady‐state conditions.

ISSN:0031-9171    

DOI:10.1063/1.1692001

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Absolute measurements of plasma density in the range8× 108to 3× 1011cm−3were made in a potassium plasma by four methods: (1) Langmuir probes, (2) microwave cavity, (3) microwave interferometry, and (4) propagation of electrostatic waves. Agreement to ≈25% between the probe and microwave measurements was achieved by careful application of probe theory. By contrast, indiscriminate use of probe theory would lead to an error of 600% at low densities. The fourth method, though less accurate, was found to be a useful independent check.

ISSN:0031-9171    

DOI:10.1063/1.1692002

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The nonadiabatic behavior of electrostatic oscillations in an initially unstable, collisionless, field‐free plasma is discussed. The equations of ordinary quasilinear theory are generalized to include the time rates of change of the oscillation frequency and the spatially homogeneous part of the distribution function. Certain aspects of the more general theory are illustrated by a discussion of the problem of interpenetrating electron and ion beams. The behavior of the instability is found to differ markedly from that predicted by quasilinear theory. Many of the findings are verified by a direct comparison with the results obtained by Buneman from computer experiments.

ISSN:0031-9171    

DOI:10.1063/1.1692003

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

An elementary analysis of frictional force suffered by a test particle traveling fast through a plasma is considered. The action of the system on the particle is described as a result due to the nonlinear polarization of the plasma. The friction thus calculated is in good agreement with that obtained on the basis of the unified theory.

ISSN:0031-9171    

DOI:10.1063/1.1692004

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

Utilizing a Krook‐type collision integral, we carry out a systematic analysis of electrostatic waves and instabilities in a fully ionized, low &bgr;, inhomogeneous plasma (where &bgr; is the ratio of particle pressure to magnetic pressure). The model employed is that of a plasma slab supported by magnetic and gravitational fields. In particular, the dispersion relations for drift waves, appropriate to a short system, and for ion cyclotron waves are derived and discussed. Thus, for drift waves it is found that in the presence of collisions, ion motion parallel to the magnetic field can provide a strong stabilizing effect for sufficiently large values of the axial wave vector. For the two‐stream ion cyclotron instability we find that ion‐ion collisions can provide strong damping even for collision frequencies well below the ion cyclotron frequency.

ISSN:0031-9171    

DOI:10.1063/1.1692005

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

The quasilinear theory of Drummond and Pines has been extended in order to include the effects of collisions, and the resulting equations have been solved in the steady state. The extent to which collisions cause a reduction in Landau damping is demonstrated. Results are given in terms of the two parameters,&ohgr;/kvande2E20/m2v3k&bgr;where &ohgr; and k are the frequency and wavenumber of the propagating wave field, of peak electric field strengthE0,vis the electron thermal speed, and &bgr; is the 90° deflection frequency of Spitzer, corresponding to an electron which moves with the phase velocity of the wave.

ISSN:0031-9171    

DOI:10.1063/1.1692006

出版商:AIP    

年代:1968

数据来源: AIP

摘要:

A study is made of the propagation properties and internal equilibrium structure of a large‐amplitude Alfve´n wave which conserves the magnitude of the magnetic‐field component tangential to the wave front but changes its direction. The propagation properties are found to be identical with those of small‐amplitude sinusoidal waves. The equilibrium wave structure is shown to involve an electric field along the wave normal. The sign and magnitude of this field are related to the rate and sense of rotation of the tangential magnetic field component as well as to the particle distributions. In certain cases the electric field may be sufficiently large to cause nonnegligible variations in particle and magnetic pressures within the wave. Observed polarizations of the magnetopause current layer may be explained by the theory.

ISSN:0031-9171    

DOI:10.1063/1.1692007

出版商:AIP    

年代:1968

数据来源: AIP