Microstability analysis of pellet fuelled discharges in MAST

Abstract

Abstract. Reactor grade plasmas are likely to be fuelled by pellet injection. This technique transiently perturbs the profiles, driving the density profile hollow and flattening the edge temperature profile. After the pellet perturbation, the density and temperature profiles relax towards their quasi-steady-state shape. Microinstabilities influence plasma confinement and will play a role in determining the evolution of the profiles in pellet fuelled plasmas. In this paper we present the microstability analysis of pellet fuelled H-mode MAST plasmas. Taking advantage of the unique capabilities of the MAST Thomson scattering system and the possibility of synchronizing the eight lasers with the pellet injection, we were able to measure the evolution of the post-pellet electron density and temperature profiles with high temporal and spatial resolution. These profiles, together with ion temperature profiles measured using a charge exchange diagnostic, were used to produce equilibria suitable for microstability analysis of the equilibrium changes induced by pellet injection. This analysis, carried out using the local gyrokinetic code GS2, reveals that the microstability properties are extremely sensitive to the rapid and large transient excursions of the density and temperature profiles, which also change collisionality and βe significantly in the region most strongly affected by the pellet ablation.

Pellet fuelling with edge-localized modes controlled by external magnetic perturbations in MAST

“…In particular we focus on the effects of pellets on ELM mitigation. This study thus complements the micro-stability survey in the pellet deposition zone [16] which addresses the inter-ELM transport.…”

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

“…However the analysis of this important process would require temporarily resolved profile data (or box car analysis) which is outside the scope of this paper. Post pellet plasmas with hollow density profiles were analysed in MAST in references [16,17]. It was found that an inverted density gradient can unfavourably suppress micro-instabilities reducing the core fuelling rate, however, this depends on the actual values of the temperature gradients after the pellet.…”

Transport analysis and modelling of the evolution of hollow density profiles plasmas in JET and implication for ITER

“…For negative R L / n no such deep investigation has been carried out. In a very recent study about pellet fuelled discharges of MAST [14], the transport properties of the hollow density, transiently driven by pellet injection, have been investigated. This first microstability analysis predicts the stabilization of the modes for negative R L / n , giving significant indications about the behaviour of the plasma in presence of hollow density profiles.…”