Abstract
Pellet injection is the primary fueling technique planned for central fueling of the ITER burning plasma, which is a requirement for achieving high fusion gain. Injection of pellets from the inner wall has been shown on present day tokamaks to provide efficient fueling and is planned for use on ITER [1,2]. Significant development of pellet fueling technology has occurred as a result of the ITER R&D process. Extrusion rates with batch extruders have reached more than 1/2 of the ITER design specification of 1.3 cm3/s [3] and the ability to fuel efficiently from the inner wall by injecting through curved guide tubes has been demonstrated on several fusion devices.
Modeling of the fueling deposition from inner wall pellet injection has been done using the Parks et al. ExB drift model [4] shows that inside launched pellets of 3mm size and speeds of 300 m/s have the capability to fuel well inside the separatrix. Gas fueling on the other hand is calculated to have very poor fueling efficiency due to the high density and wide scrape off layer compared to current machines. Isotopically mixed D/T pellets can provide efficient tritium fueling that will minimize tritium wall loading when compared to gas puffing of tritium. In addition, the use of pellets as an ELM trigger has been demonstrated and continues to be investigated as an ELM mitigation technique.
During the ITER CDA and EDA the U.S. was responsible for ITER fueling system design and R&D and is in good position to resume this role for the ITER pellet fueling system. Currently the performance of the ITER guide tube design is under investigation. A mockup is being built that will allow tests with different pellet sizes and repetition rates. The results of these tests and their implication for fueling efficiency and central fueling will be discussed. The ITER pellet injection technology developments to date, specified requirements, and remaining development issues will be presented along with a plan to reach the design goal in time for employment on ITER.
