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Comparison of Uncoated and Tungsten-Coated Electrode Performance on CTIX

Author: Robert D. Horton
Requested Type: Poster Only
Submitted: 2014-05-30 12:00:11

Co-authors: D.A. Buchenauer, D.Q. Hwang, B. Mills, R.W. Evans

Contact Info:
University of California, Davis
4435 North First Ave
Livermore, CA   94551
USA

Abstract Text:
The Compact Toroid Injection Experiment (CTIX) is currently being used to demonstrate efficient production of CT plasmas of high average atomic mass, using accretion of noble gas puffed in the acceleration region. An important application of such high-Z CTs is the suppression, by a combination of collisional and bremsstrahung effects, of highly-relativistic electrons produced by disruptions in large tokamaks. In order to produce CTs with number density and energy density relevant to this application, high power densities are required on electrode surfaces, which may result in surface damage. By coating the inner electrodes with vacuum-sprayed tungsten, such damage may be minimized. Two new inner electrodes have been constructed for CTIX, one of stainless steel and one of tungsten-coated Inconel. Experiments are underway comparing the performance of the two electrodes, using the usual magnetic and density diagnostics, combined with fast imaging of the axially-viewed plasma, and surface measurements of the electrodes after operation. Initial results indicate significantly reduced inner electrode damage (melting) with tungsten coating. Also, axial imaging measurements indicate that high performance, indicated by large axial magnetic field in the acceleration region, is associated with high azimuthal uniformity of CT visible emission. By maximizing uniformity of light emission by altering operating conditions such as voltage and gas timing, it may be possible to obtain higher-performance and more reproducible CTs for future applications.

Characterization: 1.3

Comments:

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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