The pellet rocket effect in magnetic confinement fusion plasmas

TL;DR

This paper models the pellet rocket effect in magnetic confinement fusion plasmas, showing how it accelerates pellets and impacts their penetration, which is crucial for disruption mitigation in tokamaks and ITER.

Contribution

It introduces a semi-analytical model of the pellet rocket effect, providing predictions of pellet acceleration consistent with experiments and implications for fusion reactor scenarios.

Findings

Predicted pellet accelerations match experimental estimates in tokamaks.

The effect could significantly shorten pellet penetration in ITER.

Implications for disruption mitigation strategies.

Abstract

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 ($\sim 10^5 \;\rm m/s^2$). Projections for ITER high-confinement scenarios ($\sim 10^6 \;\rm m/s^2$) indicate significantly shorter pellet penetration than expected without this effect, which could limit the effectiveness of disruption mitigation.