摘要:

Recently it was shown that, by using the analysis of electrostatic waves entering the plasma–sheath edge, the direct‐current (dc) Bohm criterion also holds for discharges under radio‐frequency (rf) conditions. In this paper, the influence of Bohm’s criterion on the sheath characteristics for generator frequencies much higher than the ion plasma frequency has been examined by means of an analysis which is baseddirectlyon the numerical solution of the Poisson equation. The present calculations indicate that for high rf voltages the time‐dependent potential profile does not always increase monotonically, even if Bohm’s criterion is fulfilled. However, as this nonmonotonic behavior does not lead to a more stringent Bohm criterion, the statement that the original dc Bohm criterion also holds in the high‐frequency regime is confirmed. The calculations show further that the time‐dependent sheath potential is almost completely modulated in the major part of the sheath and that the modulation drops abruptly to zero close to the plasma–sheath edge.

ISSN:0899-8221    

DOI:10.1063/1.860798

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A model is presented for the axial neutral particle pressure gradients and flow patterns in the positive column of a monatomic dc gas discharge. Taking into account both the charge imbalance volume force and charged‐particle momentum divergence force components, an analytical expression is derived for the driving volume force acting on the neutral particles. This expression is used to numerically solve for the pressure gradients and flow patterns for both closed and bypass discharge tube configurations. For discharges with sufficiently small current densities (e.g., a 0.2 mA, 1.5 mm radius, 5 Torr He discharge), this model yields a reversal in the pressure gradient from that predicted by previous studies where the charge imbalance volume force had been neglected. For bypass tube configurations, this pressure reversal can result in an on‐axis cathode directed neutral flow, as opposed to the previously predicted on‐axis anode directed flow.

ISSN:0899-8221    

DOI:10.1063/1.860799

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Intense short‐duration transverse mode solitons are found to exist in a ultrarelativistically hot electron–positron plasma and its relation with the pulsar radiation in discussed.

ISSN:0899-8221    

DOI:10.1063/1.860800

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Stationary inward flows of electron energy have been obtained in transport code simulations of reactive drift wave systems. The recent experimental results with off‐axis electron cyclotron heating in the DIII‐D tokamak [Phys. Rev. Lett.68, 52 (1992)] have been recovered with peaked electron temperature profiles and strong profile consistency.

ISSN:0899-8221    

DOI:10.1063/1.860801

出版商:AIP    

年代:1993

数据来源: AIP