Erosion and re-deposition in JT-60U

Goto, Yoshitaka*

Recent results of erosion and re-deposition studies are reported for graphite tiles from W-shaped divertor region of JT-60U. The tiles were operated in Jun. 1997 - Oct. 1998 periods in which more than 3000 D-D discharge experiments were made with all-carbon walls with 2-times boronizations and inner-private flux pumping. Erosion depth was estimated by using dial gauge, while deposition was measured with SEM. On the outer divertor target, erosion was found dominant, while on the inner target, re-deposition was found to be dominant. No continuous deposition layers on the dome top. Observed in/out asymmetry is attributable to in/out asymmetry of plasma particle conditions in front of the divertor plates. Columnar structures in the redeposition layers corresponded to the lower heat-flux zone, while lamellar structures were found in the overlayers in the higher heat-flux zone near the separatrix strike point.