Burning fusion plasmas require a steady state fueling source of DT fuel that can penetrate deeply into the core plasma to replenish burned fuel and losses. Developing technologies and understanding their application to efficiently and reliably fuel fusion reactors, control plasma burn through isotopic tailoring, and provide safe fast plasma terminations are our challenge.
We have pioneered and improved the technique of pellet fueling to inject solid cryogenic fuel pellets of H, D, and T into plasmas at high speeds using a reliable repeating steady-state gas gun injector. Some success stories utilizing this technique have been the record n-t Lawson parameter that was reached with repetitive pellet injection on TFTR and the discovery of the pellet enhanced performance mode with shear reversal on JET. Pellet velocities achieved in such guns range between 100-1700 m/s. Two-stage light gas guns have also been developed that operate repetitively at up to 3000 m/s. This injection technology is being developed and applied to ITER for fueling, mitigation of plasma edge instabilities, and fast plasma termination during disruptions.
Figure at top of page: Shotgun pellet injector developed by the VLT and installed on the DIII-D tokamak for disruption mitigation studies. A 15x20 mm cylindrical deuterium or neon pellet is fired against a metal plate to produce a spray of fragments and liquid gaseous mixture aimed toward the plasma axis.