Appliocation of High Z materials as Plasma Facing Materials

利用各种技术研究了高Z材料作为面向等离子体材料的性能，如氢循环、等离子体热负荷的热响应、高Z杂质的释放及其离子在等离子体中的行为。主要结论如下：（1）预热温度在800 K以上的W体限制器，除了在最高热负荷时发生轻微的表面熔化外，在几秒钟内能承受约120 MW/m^2的等离子体热负荷。（2）C/W双限制器实验提供了关于低Z和高Z材料在同时用作面向等离子体材料（PFM）时的行为的非常有用的信息，例如交叉污染过程，氢反射和沉积中的大质量差的影响等。(3)真空等离子体展向钨（VPS-W）涂层极向限制器吸收了约60%的对流热，维持了密度高达5×10^ cm^的欧姆等离子体<13><-3>。大多数VPS-W涂层限制器耐受的热负荷为20 MW/m^2。然而，一些限制器严重受损。可能它们的弯曲形状产生了强烈的热应力，导致W层剥落。在TEXTOR上进行的一系列W限制器实验表明，如果通过NBI和/或ICRH加热来避免W的中心聚集，W可以用作PFM和偏滤器板。然而，等离子体的启动困难、钨在高温等离子体中的行为以及材料的选择等问题仍然是人们关注的焦点。

Properties of high Z materials as plasma facing materials, such as hydrogen recycling, thermal response to plasma heat load, high Z impurity release and behavior of their ions in plasmas, have been examined by various technique. Main conclusions are summarized as follows,(1) The W bulk limiter operated with preheating above 800K withstood plasma heat load of about〜20MW/m^2 for a few seconds except slight surface melting during the highest heat load shot. However it was severely damaged when operated at around 500K(2) The C/W twin limiter experiments gave very useful information on how low- and high-Z materials behave for the case of simultaneous utilization as plasma facing maerials (PFM) such like cross contamination process, influences of large mass difference in the hydrogen reflection and deposition, and so on.(3) About 60% of the total convection heat was absorbed in the vacuum plasma splayed-W (VPS-W) coated poloidal limiters, and the ohmic plasma with the density as high as 5×10^<13> cm^<-3> was sustained. Most of the VPS-W coated limiters tolerated to the heat load of〜20MW/m^2. However some limiters were heavily damaged. Probably their curved shape gave strong thermal stress, resulting in the exfoliation of the W layer. Operation at below DBTT would enhance the crack propagation.These series of W limiters experiments in TEXTOR have probed that W is applicable as PFM and divertor plate, if its central accumulation are avoided by NBI and/or ICRH heating. Nevertheless, some concerns are still remaining, those are, difficulty of plasma start-up, W behavior in higher temperature plasma, and materials selection.