Enhanced plasma performance by ICRF boronization

Boronization with carborane (C₂B₁₀H₁₂) by ICRF has been applied routinely to the walls of HT-7 super-conducting tokamak for the reduction of impurity influx, especially carbon and oxygen. Significant suppression of metallic impurities and radiating power fraction are achieved. The improved confinement for both particle and energy is observed in full range of operation parameters. Energy balance analysis shows that electron heat diffusion coefficient is strongly reduced. Measurements by Langmuir probes at the edge plasma show that the poloidal velocity shear after boronization is changed to a profile favoring to good confinement. The main emphasis of this paper is to describe effects of boronization on aspects of the enhanced plasma performance.