Development of pellet injection system for KSTAR

KSTAR (Korea Superconducting Tokamak Advanced Research) has used a gas puffing system as a main fueling method since 2008. Up to date total fueling efficiency of the gas puff is less than 30%. A pellet injection is a more effective technique to control a plasma density than the gas puffing system and a supersonic molecular beam injection. Therefore, we have developed the pellet injection system for KSTAR. The pellet injection system for KSTAR consists of a pellet injector which injects pellets of a deuterium (diameter of 2 mm, length of 1.5-2 mm) at a velocity above 200 m/s with an injection frequency of 1-20 Hz, a 2-stage differential pumping system, a guide tube, a control system and so on. It is planned to inject pellets through a high field side and increase the plasma performance.