Lithium coating is applied for wall conditioning in the Sino-UNIted Spherical Tokamak-2. Two movable evaporators are installed on the equatorial plane to evaporate lithium. A novel method to handle lithium is used in this paper. Before lithium coating, stainless steel foils are put up to cover almost all of the wall except for the graphite limiter, making it extremely easy to clean lithium after experiment. Following lithium coating, the water and carbon dioxide in residual gases are reduced by more than half, and the carbon, oxygen, and nitrogen impurities during discharge are reduced by one order of magnitude. During the merging compression startup, an enhancement of ion heating is observed and attributed to a 30% increase in the total plasma current. In ohmic discharges, the energy confinement time is observed to exceed the linear ohmic confinement within the lithium wall.
This paper reports on the use of lithium coating to improve plasma performance in the SUNIST-2 spherical tokamak. Lithium coating reduced impurities and enhanced ion heating, leading to improved energy confinement. The results demonstrate the potential of lithium coatings for wall conditioning in fusion devices.