Plasma surface engineering in first wall of tokamak

Plasma facing wall condition is very important for the energy confinement o f plasma in a tokamak machine. The boronization, siliconization and lithium coating of the inner wall of HL-1M are introduced here, and the hydrogen r ecycling and influence on controlled impurities and core radiation energy l oss are discussed. Experiments show that these wall treatments are very use ful for plasma confinement; a 4-s reproducible long pulse discharge is obta ined for siliconized wall, but the plasma pulse length only achieves 2.1 s and its reproducibility is very poor for boronized wall. Lithium coating is the best method of wall treatment for lowering hydrogen recycling and decr easing the impurities level. For the applications of HL-2A and the future f usion device, a series of B, Ti, Si-doped graphite and B4C-C/C composites h ave been developed, some experimental results for chemical sputtering, trit ium retention and recycling, as well as high heat loads are reviewed. Meanw hile, SiC, TiC and B4C coating, and B4C-C, SiC-C, B4C-Cu, Mo-Cu and W-Cu fu nctionally graded materials are also introduced. (C) 2000 Elsevier Science B.V. All rights reserved.