Atomic Energy Society of Japan

To stable plasma operation in the fusion reactor, it was supply plasma experiments using an impurity powder dropper (IPD) system had been conducted as a method to actively control wall recycling. Results from the EAST (ASIPP, China) indicate that lithium is more effective than boron in controlling wall recycling, especially in maintaining high-performance plasma discharges longer than 100 s. However, the mechanism is not fully understood. This study focused on the change in plasma parameters when lithium is dropped into the plasma and compared the difference with the use of boron. Radial distribution measurements of lithium and boron by charge exchange spectroscopy show that the signal intensity of lithium increases to the core plasma at an early phase, but immediately decreases when the plasma stops. In contrast, for boron, the signal intensity at the core plasma is maintained even after the powder dropping stops, i.e., accumulation occurs.