The effect of plasmoid drifts on the pellet rocket effect in magnetic confinement fusion plasmas

TL;DR

This paper presents a semi-analytical model showing how plasmoid drifts and heat flux asymmetries influence pellet acceleration in fusion plasmas, potentially limiting pellet injection effectiveness in reactor conditions.

Contribution

It introduces a model that accounts for plasma gradients and plasmoid shielding effects on the pellet rocket effect, highlighting their impact on pellet penetration in fusion devices.

Findings

Rocket effect limits pellet penetration in high-temperature scenarios.

Plasmoid shielding dominates asymmetries for small, fast pellets.

Plasma profile variations are key in large, slow pellet regimes.

Abstract

We detail here a semi-analytical model for the pellet rocket effect, which describes the acceleration of pellets in a fusion plasma due to asymmetries in the heat flux reaching the pellet surface and the corresponding ablation rate. This effect was shown in experiments to significantly modify the pellet trajectory, and projections for reactor scale devices indicate that it may severely limit the effectiveness of pellet injection methods. We account for asymmetries stemming both from plasma parameter gradients and an asymmetric plasmoid shielding caused by the drift of the ionized pellet cloud. For high temperature, reactor relevant scenarios, we find a wide range of initial pellet sizes and speeds where the rocket effect severely limits the penetration depth of the pellet. In these cases, the plasma parameter profile variations dominate the rocket effect. We find that for small and fast pellets, where the rocket effect is less pronounced, plasmoid shielding induced asymmetries dominate.