ORNL mock-up tests of inside launch pellet injection on JET and LHD☆

Abstract In experiments on ASDEX-Upgrade and DIII-D tokamaks, the injection of D 2 pellets from the magnetic high-field side of the plasma resulted in deeper pellet penetration and improved fueling efficiency. Based on those successful experiments, fusion researchers at the Joint European Torus and the Large Helical Device decided to implement inside launch pellet injection. These injection schemes require the use of curved guide tubes to route the pellets from the acceleration devices to the inside launch locations, and the pellets are subjected to stresses from centrifugal and impact forces in traversing the tubes. Before the installations on the large experimental fusion devices, mock-ups of the guide tubes were constructed and tested at the Oak Ridge National Laboratory to determine the pellet speed limit for reliable operation without pellet fracturing. In laboratory testing of the mock-ups, it was found that the pellet speed had to be limited to a few hundreds of meters per second for intact pellets. In this paper, the test equipment and experimental results are described.