On the utilization of high Z materials as a plasma facing component
On the utilization of high Z materials as a plasma facing component
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DOI：
10.1016/s0920-3796(98)00206-3
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发表时间：
1998-09
影响因子：
1.7
通讯作者：
T. Tanabe;M. Akiba;Y. Ueda;K. Ohya;M. Wada;V. Philipps
中科院分区：
文献类型：
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作者：
T. Tanabe;M. Akiba;Y. Ueda;K. Ohya;M. Wada;V. Philipps
本文综述了近年来托卡马克装置中PFM高Z性能的研究成果，并结合高热负荷试验和表面物理数据库（溅射、反射等）等基础实验，评述了高Z PFC研究和发展中的课题。高Z PFM的危险行为是高Z杂质可能在等离子体芯中积累，并且由于它们的高辐射而伴随着等离子体崩溃。然而，最近在Alcator-C Mod、TEXTOR和USDEX-U中进行的实验表明，这种情况仅在特殊条件下发生，这些实验使用高Z材料作为偏滤器靶或限制器。主要在欧姆加热的TEXTOR等离子体中观察到高Z的积累。然而，这种积累不一定与从限制器释放的高Z杂质有关，而是很可能受等离子体中杂质输运的控制。因此，如果可以通过适当的输运控制来避免高Z杂质的中心积累，则高Z可以用作PFM。高Z原子的“瞬时再沉积”现象的出现，为高Z材料的利用提供了很好的前景。对于Z值较高的材料，由于其较高的反射系数，热沉积可能会减少，这必须在未来得到证实。Mo和W体积限制器被批准用于其DBTT以上。然而，由于源于再结晶和晶粒生长的晶间开裂在高温使用下是不可避免的，因此需要在操作温度下进行一些优化以避免脆化（较高较好）和再结晶（较低较好）以及控制晶粒结构。在这方面，具有柱状晶粒结构的CVD涂层似乎是有前途的。在等离子体加载条件下，虽然氚在Mo和W中的高温滞留量很小，但仍应考虑氢对裂纹形成的影响。
This paper summarizes recent results on high Z performance as PFM in tokamak machines and remarks upon subjects in research and development of high Z PFC referring basic experiments such as high heat load test and surface physics data base (sputtering, reflection, etc.). The dangerous behavior of high Z PFM is the possible accumulation of high Z impurities in the plasma core and accompanying plasma collapse due to their high radiation. However, recent experiments in Alcator-C Mod, TEXTOR and USDEX-U, which employ high Z materials as a divertor target or a limiter, have shown that this occurred only under special conditions. The accumulation of high Z has been observed mainly in ohmic heated TEXTOR plasma. Such accumulation is, however, not necessarily connected with the released high Z impurities from the limiter but is very likely controlled by the impurity transport in the plasma. Therefore, if the central accumulation of high Z impurities can be avoided by suitable transport control, the high Z can be used as PFM. The appearance of ‘prompt redeposition’ of high Z atoms is very promising for the utilization of high Z materials. Heat deposition is likely reduced for higher Z materials owing to its higher reflection coefficient, which must be confirmed in the future. Mo and W bulk limiters are approved to be utilized above their DBTT. However, since intergranular cracking originating from recrystallization and grain growth are unavoidable at high temperature utilization, some optimization at operating temperatures to avoid brittlement (higher is better) and recrystallization (lower is better) and control of grain structures are needed. In this respect, CVD coating with a columnar grain structure seems promising. Hydrogen effect should be taken into account for the crack formation under plasma loading conditions, though tritium retention in Mo and W at high temperatures would be small.