Hydrogenic retention with high-Z plasma facing surfaces in Alcator C-Mod
Hydrogenic retention with high-Z plasma facing surfaces in Alcator C-Mod
复制标题
DOI：
10.1088/0029-5515/49/4/045009
复制
发表时间：
2009-03
期刊：
影响因子：
3.3
通讯作者：
B. Lipschultz;D. Whyte;J. Irby;B. LaBombard;G. Wright
中科院分区：
文献类型：
--
作者：
B. Lipschultz;D. Whyte;J. Irby;B. LaBombard;G. Wright
用一种新的“静态”气体平衡方法研究了C-Mod托卡马克反应器中氘(D)燃料的滞留。C-Mod仅采用高z钼（Mo）和钨(W)作为其等离子体表面材料，并间歇应用薄硼(B)膜。研究发现，无论Mo表面是否被B膜清除或部分覆盖，每次静态放电时，主要的Mo表面保留了大量的D2气体，约20-50%。几个实验和计算表明B不可能保留大量的燃料。相反，保留发生在Mo和W表面通过离子轰击，注入和扩散到陷阱位置。大约1% D的入射离子（ΦD）对表面的影响被保留，并且在等离子体综合暴露25秒后，没有迹象表明保留率下降。保留的幅度明显大于从Mo或w的实验室研究结果中推断出来的。在战役后直接测量到的近表面的高D/Mo水平（~ 0.01），并从气体平衡中推断出来，与高入射离子通量导致的近表面高D原子密度在Mo中产生或扩大的燃料保留的捕获点相一致。C-Mod与实验室保留结果之间的差异可能是由于多种电离的B离子直接入射到表面产生陷阱，Mo（杂质，退火）的条件以及C-Mod转化器中的高通量密度（与ITER相似，但是实验室研究中使用的10 - 100倍）等因素造成的。破坏会使表面迅速升温，将被困的含氢物质释放到容器中进行回收。在破坏中释放的大量气体的测量结果与从容器中移除的瓦片的分析结果一致-活动整合的保留率非常低，比单次非破坏性排放中观察到的保留率低1000倍。
The retention of deuterium (D) fuel in the Alcator C-Mod tokamak is studied using a new ‘static’ gas balance method. C-Mod solely employs high-Z molybdenum (Mo) and tungsten (W) for its plasma facing materials, with intermittent application of thin boron (B) films. The primarily Mo surfaces are found to retain large fractions, ∼20–50%, of the D2 gas fuelled per quiescent discharge, regardless of whether the Mo surfaces are cleaned of, or partially covered by, B films. Several experiments and calculations show that it is improbable that B retains significant fractions of the fuel. Rather, retention occurs in Mo and W surfaces through ion bombardment, implantation and diffusion to trap sites. Roughly 1% D of the incident ion fluence, ΦD, to surfaces is retained, and with no indication of the retention rate decreasing after 25 s of integrated plasma exposure. The magnitude of retention is significantly larger than that extrapolated from the results of laboratory studies for either Mo or W. The high levels of D/Mo in the near surface, measured directly post-campaign (∼0.01) in tiles and inferred from gas balance, are consistent with trapping sites for fuel retention in the Mo being created, or expanded, by high D atom densities in the near surface which arise as a result of high incident ion fluxes. Differences between C-Mod and laboratory retention results may be due to such factors as the multiply ionized B ions incident on the surface directly creating traps, the condition of Mo (impurities, annealing) and the high-flux densities in the C-Mod divertor which are similar to ITER, but 10–100× those used in laboratory studies. Disruptions produce rapid heating of the surfaces, releasing trapped hydrogenic species into the vessel for recovery. The measurements of the large amount of gas released in disruptions are consistent with the analysis of tiles removed from the vessel post-campaign—the campaign-integrated retention is very low, of order 1000× less than that observed in a single, non-disruptive discharge.