REVIEW OF HIGH Z-MATERIALS FOR PSI APPLICATIONS

Application of carbon based low Z materials to PFM has significantly improved plasma parameters in large tokamaks. There are, however, serious concerns of erosion, neutron damage, etc. for application of low Z materials in the future D-T burning machine. To apply high Z metals to PFM, there are several issues to be solved: high Z impurity production by sputtering, their accumulation in the plasma center, and high radiation loss. Because of these concerns high Z metals are not widely employed nor planned to be used in the present large tokamaks. Since our efforts have been concentrated to optimize the low Z materials, little systematic investigations for high Z materials in tokamaks have been done, resulting in a poor data base especially for those materials concerning impacts on plasma core. In order to employ high Z material as PFM near future, material properties related to impurity production and hydrogen recycling are reviewed, and what is important and shall be done is also discussed.