ON THE UTILIZATION OF HIGH-Z MATERIALS AS A PLASMA-FACING COMPONENT

Citation
T. Tanabe et al., ON THE UTILIZATION OF HIGH-Z MATERIALS AS A PLASMA-FACING COMPONENT, Fusion engineering and design, 39-4, 1998, pp. 275-285
Citations number
44
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Nuclear Sciences & Tecnology
ISSN journal
0920-3796
Volume
39-4
Year of publication
1998
Pages
275 - 285
Database
ISI
SICI code
0920-3796(1998)39-4:<275:OTUOHM>2.0.ZU;2-V
Abstract
This paper summarizes recent results on high Z performance as PFM in t okamak 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 dang erous behavior of high Z PFM is the possible accumulation of high Z im purities in the plasma core and accompanying plasma collapse due to th eir high radiation. However, recent experiments in Alcator-C Mod, TEXT OR 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 connecte d with the released high Z impurities from the limiter but is very lik ely controlled by the impurity transport in the plasma. Therefore, if the central accumulation of high Z impurities can be avoided by suitab le transport control, the high Z can be used as PFM. The appearance of 'prompt redeposition' of high Z atoms is very promising for the utili zation of high Z materials. Heat deposition is likely reduced for high er 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 origi nating 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 i s 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 pla sma loading conditions, though tritium retention in Mo and W at high t emperatures would be small. (C) 1998 Elsevier Science S.A. All rights reserved.