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射频驱动频率对托卡马克装置辉光放电清洗特性的影响

Influence of RF Driven Frequency on the Tokamak Glow Discharge Cleaning Characteristics

  • 摘要: HL-2M装置初始放电阶段,分别采用2.1 MHz,13.56 MHz和40.68 MHz三种频率的射频电源开展了射频-直流辉光放电清洗实验,研究射频驱动频率对放电清洗特性的影响。预加载功率1500 W时,2.1 MHz放电的击穿气压为2.0×10−1 Pa,13.56 MHz放电为5.6×10−1 Pa;而40.68 MHz叠加直流偏压后在9.2×10−1 Pa实现击穿。对三种频率辉光放电清洗实验过程中的残余气体成分进行监测,结果表明杂质产额由高到低为:2.1 MHz>40.68 MHz>13.56 MHz。由于低频放电具有较多的加热电子数,所以2.1 MHz放电的杂质产额最高。而虽然40.68 MHz放电的功率耦合效率最低,但由于具有高的等离子体密度,其杂质产额高于13.56 MHz。可见2.1 MHz的射频-直流辉光放电在HL-2M装置初始放电阶段具有最优的清洗特性。然而由于不同频率的功率耦合效率不同,同样会对清洗效率产生影响,因此下一步首先应解决阻抗匹配问题以提高耦合功率。

     

    Abstract: In order to study the influence of RF driven frequency on the glow discharge cleaning characteristics, RF frequencies of 2.1 MHz, 13.56 MHz and 40.68 MHz are employed to perform radio-frequency glow discharge cleaning (RF-GDC) during the initial discharge phase of HL-2M. Results show that the breakdown pressure of 2.1 MHz RF-GDC is 2.0×10−1 Pa, while that of 13.56 MHz is 5.6×10−1 Pa with a preset power of 1500 W. However, the breakdown happens at 9.2×10−1 Pa only when DC bias voltage is added for the 40.68 MHz case. The impurity cleaning efficiency is also studied by monitoring the residual gas composition during the RF-GDC with different driven frequencies. Results show that, due to the more heated electrons at low frequency, the 2.1 MHz RF-GDC has the highest impurity yield. Additionally, although the 40.68 MHz RF-GDC has the lowest power coupling efficiency, its impurity yield is still higher than 13.56 MHz RF-GDC due to its high plasma density. The results indicated that the 2.1 MHz RF-GDC has the best cleaning performance. However, because the power coupling efficiency of different frequency is different, which also have an impact on the cleaning efficiency, the impedance matching problem should be solved to improve the coupling power in the next step.

     

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