Studies of the material erosion and deposition during the wall conditioning processes using quartz crystal microbalance in EAST

Abstract

To study material erosion and deposition during different wall conditioning processes in the Experimental Advanced Superconducting Tokamak (EAST), two newly developed quartz crystal microbalances (QMBs) at the mid-plane of port C (C-QMB) and port J (J-QMB) with the same radial radius were used for in-situ and real-time measurements during the 2021 autumn experimental campaign. It was found that the material deposition was mainly influenced by the location of the antenna and the power of the ion cyclotron range of frequency (ICRF), rather than the location of the gas inlet, during the wall cleaning with helium plasma and siliconization assisted with ICRF plasma. The higher energy and density of plasma could result in higher deposition rates near the antenna. While, during lithium (Li) coating, the material deposition was greatly influenced by the location of the Li oven due to the deposition of unionized Li atoms. The ICRF power influenced the material deposition behavior far away from the Li ovens. Besides, a stronger effect on impurity suppression was observed with a more uniform deposition trend of Li coating. This necessitates further study on the influence of factors such as the location of the Li oven and ICRF antenna, the temperature of ovens, and ICRF power on the homogeneity of wall conditioning.