Radiation losses of type-I ELMs during impurity seeding experiments in the full tungsten ASDEX Upgrade

Abstract

Edge localised modes (ELMs) are a serious concern for plasma facing components in next generation tokamaks. In order to keep the power load on divertor targets at a reasonable level, operation at high heating powers in ASDEX Upgrade with boronised full tungsten walls was possible only with radiative cooling by nitrogen seeding. The key player to reduce the power load is the control of the divertor radiation. This paper investigates radiation losses between and during type-I ELMs in unseeded and nitrogen seeded discharges. The ELM averaged radiation level raises from 60% of the input power in unseeded discharges to 80% in nitrogen seeded discharges. The increase of radiation during an ELM is nearly the same for seeded an unseeded discharges, but due to the smaller ELM size in seeded discharges about 40% of the ELM energy is radiated compared to 20% in unseeded discharges.