Development of pellet injector system for large helical device

A multi-pellet injector system has been developed as a fundamental fueling tool for the Large Helical Device (LHD). Since a primary goal of the LHD pr oject is demonstration of steady-state high-temperature plasmas, highly rel iable and reproducible performance is prerequisite for the LHD pellet injec tor. The helium Gifford-McMahon (GM) cycle cryogenic refrigerator and conve ntional pipe-gun mechanism have been employed along with these requirements . Since the triple point temperature of hydrogen is lower than those of iso topes; deuterium and tritium, a careful and steady temperature control is n ecessary in pellet formation. The amount of propellant gas has been minimiz ed by small reservoir to reduce heat load and inflow into the plasma vacuum chamber. Both robustness and flexibility have been realized by using the p rogrammable logic controller combined with GUI on WindowsNT. The pellet inj ector has demonstrated continuous hundreds of injection without any fail an d has been applied for the LHD experiment successfully. (C) 2000 Elsevier S cience B.V. All rights reserved.