UKAEA-CCFE-PR(25)270
The pellet rocket effect in magnetic confinement fusion plasmas
Pellets of frozen material travelling into a magnetically confined fusion plasma are accelerated by the so-called pellet rocket effect. The non-uniform plasma heats the pellet ablation cloud asymmetrically, producing pressure-driven, rocket-like propulsion of the pellet. We present a semi-analytical model of this process by perturbing a spherically symmetric ablation model. Predicted pellet accelerations match experimental estimates in current tokamaks (∼ 105 m/s2). Projections for ITER high-confinement scenarios (∼ 106 m/s2) indicate significantly shorter pellet penetration than expected
without this effect, which could limit the effectiveness of disruption mitigation.