Design of a centrifugal acceleration system for high velocity injection of impurity pellet into EAST tokamak

Abstract A centrifugal pellet injection system for high velocity impurity pellet injection to control ELMs and research impurity transport has been developed for the Experimental Advanced Superconducting Tokamak (EAST). The system is composed of the dropper, the centrifugal accelerator, vacuum pumping system and the diagnostic unit. The centrifugal accelerator is designed to accelerate the pellet by the rotating arm driven by a KYKY F100 turbomolecular pump with an adjusted rotating velocity from 0 to 42,300 rpm. In order to evaluate the stability of the rotating arm, the stress distribution of the rotating arm at different rotating velocities is analyzed by the stress field simulation, and the result shows the maximum stress of the rotating arm appears at the transition position between the large circular groove and the acceleration groove. By simulation analysis, it is noted that the arm can work steadily at 2500 rad/s (corresponding to about 398 Hz arm rotation frequency) rotating velocity and may be broken at 4000 rad/s (637 Hz). By the bench testing using the Li pellets of 1 mm diameter as injection material, it shows the centrifugal accelerator can work steadily for a long time under the condition that the rotating velocity doesn't exceed 2200 rad/s (350 Hz) and the maximum velocity of the pellet can reach 286 m/s. Based on the results of simulation and bench test, the centrifugal pellet injection system was installed and then injected Li pellets into the plasma steadily and continuously with the rotating velocity