Impurity retention by divertors. I. One dimensional models
Impurity retention by divertors. I. One dimensional models
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DOI：
10.1088/0029-5515/35/11/i06
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发表时间：
1995-11
期刊：
影响因子：
3.3
通讯作者：
P. Stangeby;J. Elder
中科院分区：
文献类型：
--
作者：
P. Stangeby;J. Elder
推导了用于预测托卡马克偏滤器何时应保留杂质的解析简单流体理论(SFT)。只考虑了最简单的一维(1-D)情况，即离子从电离点沿B向上游远处泄漏的情况。SFT直接建立在早期对偏滤器保留杂质的一维处理的基础上。我们发现，在SFT中引入跨场泄漏是必要的，这与实际偏滤器的二维情况有关，否则上游区域将遭受灾难性的、非物理的杂质积累。如果没有这一修正，即使在相当冷的(碰撞)偏滤器操作下，偏滤器泄漏预计也会发生。通过这种修正，预计只有在偏滤器温度太高而不太可能发生的情况下才会发生明显的泄漏，至少对于从靶板溅射的杂质中性粒子在它们第一次通过偏滤器等离子体风扇时被电离的情况--“浅注入”情况是这样的。因此，以前关于偏滤器保留的分析处方过于悲观。对于“深度注入”的情况，如循环气体，如霓虹灯，或墙壁溅射的源，找到了发生杂质泄漏的等离子体温度的处方。控制保留的最关键因素是杂质中性分子首先被电离的位置。将SFT的预测结果与蒙特卡罗杂质输运程序DIVIMP(偏滤器杂质)的结果进行了比较。对于强碰撞的等离子体条件，SFT被发现是非常一致的，但对于弱碰撞，SFT被发现高估了泄漏
An analytic simple fluid theory (SFT) is derived to predict when a tokamak divertor should retain impurities. Only the simplest, one dimensional (1-D), case of leakage for ions from the point of ionization, along B to points far upstream, is considered. The SFT builds directly on earlier 1-D treatments of divertor retention of impurities. It is found essential to introduce cross-field leakage into the SFT, associated with the two dimensionality of the actual divertor situation, otherwise the upstream regions suffer catastrophic, and unphysical, impurity accumulation. Without this correction, divertor leakage is predicted to occur even under rather cold (collisional) divertor operation. With this correction, appreciable leakage is predicted to occur only for divertor temperatures that are so high as to be unlikely to occur, at least for the case where impurity neutrals sputtered from the target plate are ionized on their first pass through the divertor plasma fan-the 'shallow injection' case. Thus, previous analytic prescriptions for divertor retention are too pessimistic. For 'deep injection' cases, as can occur with recycling gases such as neon, or with wall sputtered sources, a prescription is found for the plasma temperature above which impurity leakage occurs. The most critical factor governing retention is the location at which the impurity neutrals are first ionized. The predictions of the SFT are compared with results using the Monte Carlo impurity transport code DIVIMP (Divertor Impurity). Close agreement is found for plasma conditions that are strongly collisional, but for weaker collisionality the SFT is found to overestimate leakage