Observation of direct power deposition of ICRF in EAST plasma boundary

Abstract

Waves in the ion-cyclotron range of frequencies (ICRF) used for plasma heating are known to interact strongly with the scrape-off layer (SOL) plasma, potentially limiting ICRF performance. We present the evidence of direct power deposition of ICRF in the Experimental Advanced Superconducting Tokamak (EAST) plasma boundary, with two ICRF antennas and 12 MW of ICRF source power in support of high-power and long-pulse operation. By applying Retarding Field Analyzer (RFA) diagnostic, a sharp rise in average collected ion parallel energy was obtained during the period of ICRF heating as the RFA probe stayed still at 2 mm behind the main limiter which indicates that a certain amount of power is deposited near the limiter instead of being absorbed by the main plasma. A significant increase of the target floating potential in electron temperature measured by Divertor Langmuir Probes arrays was observed. The wall temperature in the far SOL was also enhanced. As a consequence, an enhancement of the carbon and tungsten impurity concentration was observed both at the plasma boundary and core. Besides, plasma radiation, the impurity concentration of the boundary and core increased, and the temperature rise of the first wall was also observed, which are intuitive and powerful pieces of evidence of ICRF direct power deposition at the boundary.