Wall conditions on HL-2A and HL-3 tokamaks

• With offline and in-situ siliconization experiments in HL-2A, results indicate that offline siliconization could improve the plasma performance and in-situ siliconization has the same effect as offline process without any impact on plasma discharge. • The radio frequency assisted glow discharge tests in presence of the magnetic field on HL-2A demonstrate that the uniform glow discharge can be achieved with the appropriate power and pressure. • The density and temperature of the HL-3 glow discharge plasma have been measured to confirm its performance. • The breakdown voltages and pressures associated with glow discharge or radio frequency in HL-3 have been determined under various conditions. This paper presents the wall conditioning of HL-2A and HL-3 tokamaks. It details the enhancement of plasma performance achieved through siliconization processes on the HL-2A tokamak, encompassing both offline and in-situ methodologies. A study on the impact of offline siliconization on impurity concentration within HL-2A is presented, and real-time siliconization results demonstrate that it has no effect on plasma discharge. The findings indicate that in-situ siliconization is equally effective as the offline process with regard to plasma performance. With appropriate 13.56 MHz radio frequency (RF) power and pressure, a uniform glow discharge was achieved under 0.1 T in HL-2A. The effectiveness of impurity removal on HL-3 at different baking temperatures has been investigated. Measurements of glow discharge plasma density and temperature reveal that the parameters farthest from the electrode are 6 eV and ∼ 8 × 10 12 m −3 . Based on the breakdown tests, it was determined that the minimum breakdown voltage is approximate 430 V, and the lowest breakdown pressure is around 2.1 × 10 -2 Pa when using 2.1 MHz RF power. Furthermore, experiments were conducted to investigate the efficiency of radio frequency assisted glow discharge cleaning for impurity removal. The study also evaluated the effectiveness of various methods for removing impurities. Additionally, siliconization on HL-3 was implemented successfully with determination of all key control parameters.