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Measurement of non-Maxwellian electron velocity distributions in a reflex discharge

Published online by Cambridge University Press:  13 March 2009

C. R. Phipps Jr
Affiliation:
University of California, Los Alamos Scientific Laboratory, Los Alamos, NM 87544
D. Bershader
Affiliation:
Deparment of Aeronautics and Astronautics, Leland Stanford Junior University, Stanford, California 94305

Abstract

Thomson scattering was used to determine space- and time-resolved electron velocity distribution components parallel and transverse to the magnetic field direction in a Penning-type reflex discharge in hydrogen. Electron densities were of the order 1013 cm-3, and temperatures about 3eV. For magnetic field strengths less than about 200 G, Maxwellian distributions were obtained over an energy range six times the thermal energy. Temperatures were in excellent agreement with Langmuir probe data. However, for fields of about 4500 G chaotic plasma potentials were observed with the Langmuir probe. In this regime, in which the plasma was unstable, Thomson scattering showed electron velocity distributions having central temperatures of about 2eV and wing temperatures of 15–20 eV. The experiment design employed led to extremely low stray light levels permitting clean measurements at the laser wavelength and detection of scattered signals as faint as two photons.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1978

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