Plasma detachment in JET Mark I divertor experiments

Abstract

The experimental characteristics of divertor detachment in the JET tokamak with the Mark I pumped divertor are presented for ohmic, L mode and ELMy H mode experi- ments with the main emphasis on discharges with deuterium fuelling only. The range over which divertor detachment is observed for the various regimes, as well as the influence of divertor cong- uration, direction of the toroidal eld, divertor target material and active pumping on detachment, will be described. The observed detachment characteristics, such as the existence of a considerable electron pressure drop along the eld lines in the scrape-o layer (SOL), and the compatibility of the decrease in plasma flux to the divertor plate with the observed increase of neutral pressure and D emission from the divertor region, will be examined in the light of existing results from analytical and numerical models for plasma detachment. Finally, a method to evaluate the degree of detachment and the window of detachment is proposed, and all the observations of the JET Mark I divertor experiments are summarized in the light of this new quantitative denition of divertor detachment.