Pellet refuelling of particle loss due to ELM mitigation with RMPs in the ASDEX Upgrade tokamak at low collisionality

TL;DR

This study demonstrates complete plasma density refuelling during ELM mitigation with RMPs in ASDEX Upgrade, showing pellet injection can compensate for density loss but energy confinement remains affected.

Contribution

It shows that pellet refuelling can fully compensate for density loss caused by ELM mitigation with RMPs at low collisionality in a tokamak.

Findings

Pellet injection restores plasma density after ELM mitigation.

Density pump-out requires doubling the fueling rate.

Energy confinement and pedestal temperatures are not fully recovered.

Abstract

The complete refuelling of the plasma density loss (pump-out) caused by mitigation of Edge Localised Modes (ELMs) is demonstrated on the ASDEX Upgrade tokamak. The plasma is refuelled by injection of frozen deuterium pellets and ELMs are mitigated by external resonant magnetic perturbations (RMPs). In this experiment relevant dimensionless parameters, such as relative pellet size, relative RMP amplitude and pedestal collisionality are kept at the ITER like values. Refuelling of density pump out requires a factor of two increase of nominal fuelling rate. Energy confinement and pedestal temperatures are not restored to pre-RMP values by pellet refuelling.