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Impurity studies and electrode improvements for CTIX

Author: Dean A. Buchenauer
Requested Type: Poster Only
Submitted: 2012-12-07 17:38:17

Co-authors: R.D. Horton, B.E. Mills, J.A. Whaley, S.B. Van Deusen, R. Klauser, R.W. Evans, and D.Q. Hwang

Contact Info:
Sandia National Laboratories
7011 East Avenue
Livermore, CA   94550
USA

Abstract Text:
Control of plasma impurities and electrode lifetime in compact toroid (CT) accelerators are critical for tokamak fueling and disruption control by CT plasmas. In the Compact Toroid Injection Experiment (CTIX), collector probes positioned at the accelerator exit have been used to measure impurity generation and transport. RBS analysis of electrode materials (Fe, Ni, Cu, Cr) on the collector probes has demonstrated a reduction in impurity generation through the use of active switching (2X), although there is an increase in impurity generation with acceleration voltage similar to that found with passive switching. Localized melting observed on the inner electrode (cathode) has motivated the design of a new electrode structure optimized to support a tungsten coating. Tungsten is desirable due to its high sputtering threshold and low rate, high melting temperature and good thermal conductivity, and chemical compatibility with hydrogen. Details of the design for the ~ 2 m long electrode, considerations in optimizing the vacuum plasma spray coating, and 1-d thermal calculations showing the improved performance over stainless steel surfaces will be presented.

Characterization: 1.3

Comments:
CTIX #2 (Group abstract)