Molybdenum, Carbon and Silicon Carbide Limiter Experiment in the JFT-2 Tokamak

Molybdenum, pyrolitic graphite (PG), and silicon carbide were used for the limiter of the JFT-2 tokamak. It was found that the macroscopic discharge characteristics with the PG and SiC limiters were equivalent to those with the Mo limiter, though CV line radiation with the PG and SiC limiters was 1.3 to 6 times that with the Mo limiter. For these conditions , the maximum surface temperature of the limiter during discharge was 550°C for Mo, 1900°C for PG, and 1000°C for SiC, as observed by an infrared camera. Residual gas analysis indicated that chemical reaction between the plasma and the limiter did not play a major role in carbon generation into the plasma. The estimated amount of carbon contamination of the plasma can be caused by physical sputtering, which has been separately investigated for PG.