Pellet delivery and survivability through curved guide tubes for fusion fueling and its implications for ITER

Injection of solid hydrogen pellets from the magnetic high-field side will be the primary technique for depositing fuel particles into the core of International Thermonuclear Experimental Reactor (ITER) burning plasmas. This injection scheme will require the use of curved guide tubes to route the pellets from the acceleration devices to the inside wall launch locations. Experimental pellet studies with curved guide tubes have been carried out for several years at the Oak Ridge National Laboratory (ORNL), including mock-up tests of guide tube installations for several fusion experiments. In general, the tightest bend radius of the guide tube is the key parameter in limiting intact pellet speed, and for inside launch the pellet speed is typically limited to a few hundreds of meters per second for reliable delivery of intact pellets. Recently, an experimental mock-up of the proposed ITER curved guide tube for inside wall pellet launch was set up in the lab and tested with nominal 5.3-mm D₂ pellets. For this mock-up, the pellet speed had to be limited to ≈300 m/s for reliable delivery of intact pellets. Also, microwave cavity mass detectors located upstream and downstream of the test tube indicated that ≈10% of the pellet mass was lost in the guide tube at 300 m/s. The test results from the previous mock-ups will be summarized in the paper, and the new data from the ITER mock-up will be presented and discussed.