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Characterization of a spheromak plasma gun: The effect of refractory electrode coatings

Brown, M. R. and Bailey, A. D., III and Bellan, P. M. (1991) Characterization of a spheromak plasma gun: The effect of refractory electrode coatings. Journal of Applied Physics, 69 (9). pp. 6302-6312. ISSN 0021-8979.

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In order to investigate the proposition that high-Z impurities are responsible for the anomalously short lifetime of the Caltech spheromak, the center electrode of the spheromak plasma gun has been coated with a variety of metals (bare steel, copper, nickel, chromium, rhodium, and tungsten). Visible light (230–890 nm) emitted directly from the plasma in the gun breech was monitored for each of the coated electrodes. Plasma density and temperature and spheromak lifetime were compared for each electrode. Results indicate little difference in gun performance or macroscopic plasma parameters. The chromium and tungsten electrodes performed marginally better in that a previously reported helicity injection effect [Phys. Rev. Lett. 64, 2144 (1990)] is only observed in discharges using these electrode coatings. There are subtle differences in the detailed line emission spectra from the different electrodes, but the spectra are remarkably similar. The fact that (1) contrary to expectations, attempts to reduce high-Z impurities had only marginal effect on the spheromak lifetime coupled with (2) an estimate of Zeff<2 based on a 0-D model suggests that it is not impurities but some other mechanism that limits the lifetime of small, cold spheromaks. We will discuss the general characteristics of the spheromak gun as well as effects due to the coatings.

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Additional Information:Copyright © 1991 American Institute of Physics. Received 27 September 1990; accepted 23 January 1991. It is a pleasure to acknowledge the technical assistance of M&T Plating, Frank Cosso, and Larry Begay, as well as useful discussions with Dr. Cris Barnes, Dr. Tom Jarboe, and Dr. Juan Fernández of Los Alamos National Laboratory and Dr. Charles Hartman and Dr. Jim Hammer of Lawrence Livermore National Laboratory. This work was performed under DOE Grant No. DE-FG03-86ER53232.
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Deposited On:18 Dec 2007
Last Modified:26 Dec 2012 09:48

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