Mass transfer in long pellet guiding systems at ASDEX upgrade and JET

Guiding systems used for transfer of cryogenic pellets to the tokamak inboard currently undergo optimisation to possibly extend the operational range of Inboard pellet injection scenarios. Work reported here has been concentrating on experimental studies and calculations of pellet mass loss during transfer in a guiding tube as a function of pellet parameters such as velocity and ice composition, and guiding track characteristics such as vacuum conductance, geometry, size and shape of cross-section. Results from ASDEX Upgrade and ORNL systems suggest, that centripetal loads on the pellets due to small radii bends in the systems strongly increase the erosion of pellet ice. A deleterious effect of accumulated gas due to sublimated D2-ice blocking the tube and eroding subsequent pellets has been found. However, an efficient vacuum pumping set up for a given pellet repetition rate can significantly improve the mass conservation with respect to closed tube systems.