Experimental Design of the Pellet Ablation Test Stand at Columbia University

A novel cryogenic pellet injection test stand is under development at Columbia University in collaboration with Oak Ridge National Laboratory in support of the ITER Disruption Mitigation System (DMS) using shattered pellet injection. The experiment will fabricate cryogenic pellets of various compositions and measure ablation rates from well-defined particle sources. A custom gas manifold system allows for precise control of pellet composition; including varying homogenous mixtures of hydrogen isotopes and noble gasses, and different spatial compositions with radial variation (shells) and axial variation (end caps). Pellet formation and injection are carried out by the 'pipe gun' method, where gas is fed to a cold zone held below the triple-point temperature for controlled desublimation, then propelled by a low temperature copper mechanical punch. The primary research purpose is to validate several models of ablation rates, to further the understanding of DMS pellet behavior. This setup facilitates additional investigation of the pellet freezing process, long-lifetime pellet degradation, and 'dusty' pellets with solid powders, knowledge necessary for improving DMS physics and technology in fusion pilot plants.