Study on enhancement of current drive efficiency in long RF current drive plasmas

托卡马克装置的稳态运行是实现高性价比聚变电站的关键。对TRIAM-1 M（R=0.8m，a × B = 0.12 × 0.18m，B_t<8 T）进行了LH电流驱动的研究，观察到了增强电流驱动（ECD）模式，伴随着能量约束的改善，能量电子的直接损失可能是电流驱动效率降低的主要原因。因此，测量高能电子的约束时间是非常重要的，在等离子体的低场一侧，测量了高能电子的瞬时损失的绝对值，作为可移动限制器的热输入。事实上，测量是在等离子体中进行的，所述等离子体由65 kW的注入RF功率维持，并且估计的高能电子的存储能量为约500 J。测量的热通量为约0.5 kW，并且对可移动限制器的大部分热输入来自SOL等离子体。另外，在ECD模式下，高能电子的涟漪损耗增加，这表明高能电子损耗的改善对电流驱动效率的提高没有明显的作用。

Steady state operation of tokamak is a key for the realization of cost-effective fusion power plant. TRIAM-1M (R=0.8m, a x b = 0.12 x 0.18m, B_t<8T) is positively tackled with the study of LH current drive The enhanced current drive (ECD) mode which accompanied with the improvement of energy confinement, could be observed.The direct loss of passing energetic electrons may play an essential role in reduction of current drive efficiency. Therefore, the measurements of the confinement time of energetic electrons are important.The absolute value of the prompt loss of energetic electrons was measured as the thermal input on the movable limiter located in the low field side of the plasma. In fact, the measurement was carried out in the plasma sustained by injected RF power of 65 kW and the estimated stored energy of energetic electron was about 500 J. The measured heat flux is about 0.5 kW and most of the thermal input to the movable limiter came from SOL plasma. In addition, ripple loss of energetic electron is enhanced in ECD mode.This clearly shows that the improvement of the loss of energetic electrons does not play a significant role in the enhancement of current drive efficiency.