A TECHNIQUE FOR PRODUCING LARGE DUAL-LAYER PELLETS IN SUPPORT OF DISRUPTION MITIGATION EXPERIMENTS

摘要

A special single-shot pellet injection system that produces and accelerates large cryogenic pellets (-16 mm diameter and composed of D_2 or Ne) to relatively high speeds (>300 and 600 m/s, respectively) was previously developed at the Oak Ridge National Laboratory. Subsequently, a similar system was installed on DIII-D and used successfully in disruption mitigation experiments. To circumvent some operational issues with injecting the large Ne pellets, a technique has been developed in which a relatively thin layer (0.1 to 1.0 mm) of D_2 is frozen on the inner wall of the pipe-gun barrel, followed by filling the core with solid Ne. A fast solenoid valve operating with a light gas (H_2 or He) at relatively high pressure (-70 bar) provides the force necessary to break away the dual-layer pellet and accelerate it. The technique and the initial laboratory tests are described, as well as the implementation and operational issues for fusion experiments.