Effect of lithium coating on long pulse high performance plasma discharges in EAST

Abstract

Control of impurities, fuel recycling and hydrogen content by lithium evaporative coatings and real-time lithium powder injection (LPI) in EAST are studied for high performance H-mode discharges of up to ∼100 s. The results show that the lithium evaporative coatings significantly reduced both the low-Z impurity carbon and high-Z impurity tungsten as well as molybdenum concentration in the plasmas, and the impurities concentration significantly reduced with the accumulated lithium coatings and maintained well afterwards. Specifically the high-Z tungsten core impurity concentration was maintained between 3 ppm-15 ppm during the 101 s H-mode discharge, which is acceptable for the long pulse operation. In addition, real-time wall conditioning via LPI successfully reduced the core high-Z metal impurities by 50% during ∼35 s long pulse H-mode discharge, exhibiting strong compatibility between real-time LPI with long pulse discharges. In addition, evaporative lithium coatings demonstrated fuel recycling control, with fuel recycling obviously reducing with lithium coatings and maintaining well afterwards. Also, the lithium evaporative coatings reduced the hydrogen minority species content, represented by the density ratio H/(H + D), from ∼50% down to ∼5% with accumulated lithium coatings; low hydrogen fraction improved the ICRF minority heating efficiency. Finally the real-time LPI reduced the recycling coefficient Rglobal from 0.95 to 0.82. With these wall conditionings help, the plasma density controlled well during the 101 s long pulse H-mode discharge. These results provide valuable references on impurities, fuel recycling and hydrogen content control for future longer pulse high performance H-mode operation (≥400 s) in EAST and future fusion devices.