Plasma surface engineering in first wall of tokamak

Plasma facing wall condition is very important for the energy confinement of plasma in a tokamak machine. The boronization, siliconization and lithium coating of the inner wall of HL-1M are introduced here, and the hydrogen recycling and influence on controlled impurities and core radiation energy loss are discussed. Experiments show that these wall treatments are very useful for plasma confinement; a 4-s reproducible long pulse discharge is obtained 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 decreasing the impurities level. For the applications of HL-2A and the future fusion device, a series of B, Ti, Si-doped graphite and B4C–C/C composites have been developed, some experimental results for chemical sputtering, tritium retention and recycling, as well as high heat loads are reviewed. Meanwhile, SiC, TiC and B4C coating, and B4C–C, SiC–C, B4C–Cu, Mo–Cu and W–Cu functionally graded materials are also introduced.