Boundary physics experiments on the HL-1 tokamak

Abstract In the HL-1 tokamak ohmic heating discharges with low Z eff (≈1.6) and low show a q ( a ) (≈1.8) have been obtained by using a combination of a graphite rail limiter, efficient mixed Kr-H 2 50 Hz AC discharge clearing, Ti-gettering, programmed multiple gas puffing, and controlled rise of the plasma current. The highest central density achieved was n e (0) = 1 × 10 20 m −3 . In the high density regime MARFEs and detached plasmas have been observed. In this paper the improved parameter range is discussed as it is apparent from the Hugill diagram; the behaviour of neutral hydrogen and its scaling is presented in detail and the plasma material interaction on typical limiter material has been studied by means of graphite test samples exposed to the scrape-off plasma.