Pellet Rocket Effect in Magnetic Confinement Fusion Plasmas

Pellets of frozen material traveling into a magnetically confined fusion plasma are accelerated by the so-called pellet rocket effect. The nonuniform plasma heats the pellet ablation cloud asymmetrically, producing pressure-driven, rocketlike propulsion of the pellet. We present a semianalytical model of this process by perturbing a spherically symmetric ablation model. Predicted pellet accelerations match experimental estimates in current tokamaks (∼10^{5}  m/s^{2}). Projections for ITER high-confinement scenarios (∼10^{6}   m/s^{2}) indicate significantly shorter pellet penetration than expected without this effect, which could limit the effectiveness of disruption mitigation.