Study of Impurity Control by Siliconization on HL-2A Tokamak

The plasma impurity and recycling could be effectively controlled by siliconization, which is a conventional wall conditioning method for HL-2A Tokamak. The recent progress of the siliconization system and the impurity control behavior by siliconizaition on HL-2A are introduced. The siliconization system includes two subsytems: one is used for the offline siliconization experiment which employs glow discharge for coating, and the other one is used for the real-time siliconization experiment which implements coating during plasma discharge. The experimental results show that the oxygen impurity is significantly reduced after offline siliconization, but it will gradually increase following the plasma discharge experiment. The offline siliconization effect lasted for about 150 shots. In order to make further study, real-time siliconization was developed on HL-2A. The results show that carbon, oxygen and iron levels all drop during the real-time siliconization. The amounts of H₂O and CO in the vacuum vessel were decreased after both the offline and real-time siliconization, while the real-time siliconization consumed less gas. The plasma performance of HL-2A was effectively improved by siliconization. The study provides an important technical support for the wall conditioning of the future steady-state operation fusion device.