A model for the breaking limits of D2 pellets and its application to the Tore Supra injector

An efficient control of the plasma density by pellet injection in the present and future machines, like ITER, requires a very high reliability of the injector. After ice fabrication, cutting, acceleration and transport of the pellets are potential pellet breakage sources. In order to improve the overall reliability, it is important to characterize experimentally the breakage process and to be able to calculate the corresponding limits, in particular when straight or curved guide-tubes are used to transport pellets into the plasma. In this paper we study the breakage of pellets during acceleration, collection and propagation in a guide-tube and we compare the results of an original model to the experimental observations obtained with the Tore Supra Centrifugal Pellet Injector (CPI. built by ORNL). (authors)