Comparison of different pellet injection systems for ELM pacing

ELM control in ITER is important to avoid the rapid erosion of plasma facing components (PFC) and core plasma pollution. Pacing and mitigation of ELMs can be achieved by injection of cryogenic deuterium pellets into the plasma. Successful control relies on precisely timed reliable delivery of pellets with reasonable size and velocity. To minimize unwanted fuelling constraints high speed and small pellet size seem of advantage. Efforts to develop pellet launcher systems optimised for pacing purposes have been undertaken, based on the two major accelerator types, the centrifuge and the gas or blower gun.