Effect of edge ion temperature on the divertor tungsten sputtering in WEST

Abstract

The influence of upstream ion temperature in the scrape-off layer (SOL) on the tungsten (W) sputtering in the divertor is studied in the WEST tokamak. For an almost constant power into the SOL, the upstream ion temperature and its ratio over the electron temperature gradually increase with the decrease of electron density in the SOL. This increment is observed to enhance the energy transfer from ions to electrons. This increases the downstream electron temperature and by coupling of electrons and ions, the impact energy of ions causing W sputtering in the divertor. This enhancement mechanism may become crucial to sputtering the W material for high upstream Ti/Te ratio since the impact energy of ions in the divertor would increase accordingly.