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arXiv · 1312.0523

Plasmas generated by ultra-violet light rather than electron impact

R. N. Franklin·J. E. Allen·D. M. Thomas·M. S. Benilov
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Abstract

We analyze, in both plane and cylindrical geometries, a collisionless plasma consisting of an inner region where generation occurs by UV illumination, and an un-illuminated outer region with no generation. Ions generated in the inner region flow outwards through the outer region and into a wall. We solve for this system's steady state, first in the quasi-neutral regime (where the Debye length $λ_D$ vanishes and analytic solutions exist) and then in the general case, which we solve numerically. In the general case a double layer forms where the illuminated and un-illuminated regions meet, and an approximately quasi-neutral plasma connects the double layer to the wall sheath; in plane geometry the ions coast through the quasi-neutral section at slightly more than the Bohm speed $c_s$. The system, although simple, therefore has two novel features: a double layer that does not require counter-streaming ions and electrons, and a quasi-neutral plasma where ions travel in straight lines with at least the Bohm speed. We close with a précis of our asymptotic solutions of this system, and suggest how our theoretical conclusions might be extended and tested in the laboratory.

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R. N. Franklin, J. E. Allen, D. M. Thomas, M. S. Benilov. 2013-12-02. Plasmas generated by ultra-violet light rather than electron impact. https://doi.org/10.1063/1.4848715

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