基于超声分子束和普通充气的聚变等离子体密度反馈实验研究

本文介绍了全超导托卡马克装置EAST实验中等离子体密度反馈的方法和结果. EAST密度反馈采用普通充气 (gas puffing) 和超声分子束 (supersonic molecule beam injection, SMBI) 在放电过程中反馈进气, 获得稳定、预期的等离子体密度. 典型的一天放电实验中, 每次放电的充气量和壁滞留的变化可分为两个阶段: 第一阶段为初始约20次放电, 该阶段充气量非常高且呈指数趋势下降, 粒子滞留率为80%–90%, 壁滞留迅速上升. 第二阶段为随后的约50次放电, 该阶段充气量较小且保持稳定, 粒子滞留率为50%–70%, 壁滞留缓慢上升. SMBI的加料效率为15%–30%, 延迟时间小于5 ms. 因此使用SMBI 进行密度反馈效果优于gas puffing反馈, 相同条件下前者充气量较后者减少了～ 30%, 壁滞留减少了～ 40%, 再循环系数也相应减少. gas puffing反馈时, 采用脉宽调制模式效果优于脉幅调制模式. SMBI密度反馈可以作为未来EAST长脉冲高参数放电的主要手段之一. 关键词： 密度反馈 超声分子束 再循环 壁滞留

Investgation of gas puffing and supersonic molecular beam injection density feedback expriments on EAST

To achieve desirable plasma density control, supersonic molecular beam injection (SMBI) feedback control system has been developed on EAST tokamak recently. The performance of SMBI is compared with that of gas puffing feedback system. The performance of pulse width mode is better than that of pulse amplitude mode when gas puffing is used for density feedback control. In one-day experiment scenario, the variation of gas input and wall retention can be clarified into two stages. In the first stage the retention ratio is as high as 80%–90%, and the gas input is of about the order of 10²². However, in the second stage, the retention ratio is in a range of 50%–70%. The gas input of a single discharge is small and the net wall retention grows slowly. The result of SMBI feedback control experiment is also analyzed. The shorter delay time of SMBI makes it more quickly to feedback control the plasma density. Result shows that, compared with gas puffing, the gas input of SMBI decreaseds ～ 30% and the wall retention is reduced ～ 40%. This shows SMBI’s advantage for the long pulse high-density discharges in EAST.
Keywords： density feedback supersonic molecular beam recycling wall retention