AIP Digital Archive
Electrical Engineering, Measurement and Control Technology
A retarding energy analyzer, JANUS [A. S. Wan, T. F. Yang, B. Lipschultz, and B. LeBonbard, Rev. Sci. Instrum. 57, 1542 (1986)], has been developed at MIT which has the capability of measuring the local electron temperature, ion temperature, and sheath potential in the scrape-off layer of a plasma. This offers a useful tool in the study of material development for the divertor target to be considered for ITER. The radial profile of sheath potential (φw) on tungsten surfaces has been measured in the boundary layer of Alcator C plasma using this analyzer. Simultaneous measurement of the electron temperature (Te) and ion temperature (Ti) profiles were also made. The retarding grids of the JANUS analyzer were made of fine screens, which made it difficult to determine the absolute values of the ion and electron current. A new analyzer under development replaces the screen with slits, making determination of the absolute currents, ne, and ni easier. This analyzer will be calibrated and tested on a compact tandem mirror machine, the PPEX, that is currently operational at MIT. This work was supported by U.S. DOE contract No. DE-AC02-78ET51053, AFOSR, and NASA/JPL.
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