MIGRATION OF TUNGSTEN ERODED FROM DIVERTOR TILES IN ASDEX UPGRADE

Tungsten migration in ASDEX Upgrade was investigated by analysis of de position on long term sample probes and by erosion and deposition stud ies using two probe manipulator systems in the midplane and the outer divertor plate respectively. Divertor retention was determined by meas uring the total tungsten production in the divertor and comparison wit h the spectroscopically measured tungsten content in the confined plas ma. The fraction of tungsten deposited on limiters in the main chamber compared to deposition in the divertor was determined by injecting tu ngsten into the main plasma using laser ablation and determining the d eposition of these atoms on collector probes. The ratio of inner diver tor to outer divertor tungsten deposition was obtained from surface an alysis of long term sample probes.