Density control by pellets in plasmas with ELM mitigation by RMPs in the ASDEX Upgrade tokamak

Abstract

This paper describes the extension of the previous experimental database on density control by pellets and ELM control by RMPs in the ASDEX Upgrade tokamak. A stationary low triangularity plasma is sustained by simultaneous pellet fuelling and RMP ELM control at ion pedestal collisionality of ν*i,ped ∼ 0.5. Refuelling of the RMP induced density pump-out requires a pellet rate of Φpel ∼ 0.073 Paux/Tt,ped. The duration of refuelling of density pump-out can be minimised to about 3 energy confinement times. Pellet fuelling increases or preserves ion pedestal pressure with respect to unfuelled ELM suppressed/mitigated phase. Pellets cause transition from ELM suppression to ELMy regime: At low triangularity, the first pellet triggers a transition to an ELMy phase but subsequent ELMs are not modulated by pellets. At elevated triangularity, initial pellets trigger ELM-like events but in-between pellets ELM suppression is preserved. In later phase, as density increases the plasma transitions to an ELMy phase similar to low triangularity case.