Improved Stop Cylinder Loading Scheme for a Centrifuge Pellet Accelerator

In order to perform plasma refueling experiments with cryogenic hydrogen pellets at the midsize tokamak ASDEX Upgrade, a centrifuge injector was developed based on the novel stop cylinder principle. Following the demonstration of excellent performance with this instrument, similar injectors were constructed for two of the world’s largest tokamaks, JET and JT-60U. The extended fuel consumption in these tokamaks enforced the employment of continuous extruders instead of a storage cryostat, requiring an increase in pellet temperature from 8 to 14 K. Degradation of the injector performance was found at these higher pellet temperatures due to increased gas evaporation rates but could be eliminated by a revised acceleration scheme. Applying the adapted setup, reliable and stable operation has been realized with JET and JT-60U injectors.