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Free double layers in mercury-arc discharges

Published online by Cambridge University Press:  13 March 2009

Homero Santiago Maciel  and
J. E. Allen
Homero Santiago Maciel
Affiliation:
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, U.K.
J. E. Allen
Affiliation:
Department of Engineering Science, University of Oxford, Oxford OX1 3PJ, U.K.
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Abstract

A study has been carried out of free double layers formed within the plasma volume of a low-pressure mercury-arc discharge at high current densities. The free double layer is observed to form as a visible boundary, which drifts slowly from the central section of the discharge. Current-driven instabilities are observed as the discharge current is gradually increased to a critical value, at which current limitation is observed to occur. This process, which is accompanied by high-current spikes, ceases when the free double layer becomes visible as a sharp boundary dividing the discharge column into two regions of different luminosities. The layer is observed to form in the later stages of current limitation, the onset of which occurs for a ratio of drift to thermal speed of electrons of about unity. Electrical energy is converted by the layer into kinetic energy of the charged particles. Accordingly, high-energy ions were measured by means of an electrostatic energy analyser. The multiple-sheath character of the free ‘double layer’, which is inferred from probe measurements of potential profiles, is discussed and comparisons with other space-charge structures with the same topology are made.

Type
Research Article
Information
Journal of Plasma Physics , Volume 42 , Issue 2 , October 1989 , pp. 321 - 352
Copyright
Copyright © Cambridge University Press 1989

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