H-mode achieved by pellet injection in experimental advanced superconducting tokamak

High-confinement (H-mode) plasma was achieved by injecting frozen deuterium pellets in the experimental advanced superconducting tokamak (EAST). Interesting phenomena of the simple and two-stage low-high confinement (L-H) transitions are observed in EAST with radio frequency heating after pellet injection. The results of the L-H transitions induced by pellets are discussed in detail with different theories. It is found that pellet injection in EAST can reduce the power threshold of the H-mode. Furthermore, the pellet-induced edge density gradient is an important parameter affecting the L-H transition. This investigation would be useful for the analysis of the feasibility of H-mode access by pellet injection in future devices, such as ITER.