EXPERIMENTAL STUDY OF THE PROPELLANT GAS LOAD REQUIRED FOR PELLET INJECTION WITH ITER-RELEVANT OPERATING PARAMETERS

摘要

An existing pipe gun test facility at ORNL was used for an experimental study of propellant gas loads required for ITER-relevant pellet injection, with the key objective of determining the minimal amount of gas required for optimal pellet speeds. Two pellet sizes were tested, with nominal 4.4 and 3.2 mm diameters comparable to pellets planned for fueling and ELM pacing in ITER, respectively. A novel scheme was used to freeze solid pellets from room temperature gas; this facilitated operations at higher temperatures (14.5 to 16.5 K, similar to those planned for extruder operations for ITER pellet injectors) and thus lower pellet breakaway pressures and gas loads. Most of the single-shot D_2 pellet tests were carried out with a relatively low H_2 propellant gas load of ～0.0133 bar-L. Some limited testing was also carried out with a mixed propellant gas that consisted mostly of D_2, which is more representative of the gas that will be used for ITER pellet injection. In testing it was found that this reference gas load resulted in pellet speeds in close proximity to a speed limit (～300 m/s) previously determined in a series of tests with D_2 pellets shot through a mock-up of the curved guide tubes planned for the ITER installation (for pellet fueling from the magnetic high-field side). The equipment, operations, and test results are presented and discussed, with emphasis on the relevance for ITER operations.