Comparing spontaneous and pellet-triggered ELMs via non-linear extended MHD simulations

Abstract

Injecting frozen deuterium pellets into an ELMy H-mode plasma is a well established scheme for triggering edge localized modes (ELMs) before they naturally occur. Based on an ASDEX Upgrade H-mode plasma, this article presents a comparison of extended MHD simulations of spontaneous type-I ELMs and pellet-triggered ELMs allowing to study their non-linear dynamics in detail. In particular, pellet-triggered ELMs are simulated by injecting deuterium pellets into different time points during the pedestal build-up described in [A. Cathey et al. Nuclear Fusion 60, 124007 (2020)]. Realistic ExB and diamagnetic background plasma flows as well as the time dependent bootstrap current evolution are included during the build-up to capture the balance between stabilising and destabilising terms for the edge instabilities accurately. Dependencies on the pellet size and injection times are studied. The spatio-temporal structures of the modes and the resulting divertor heat fluxes are compared in detail between spontaneous and triggered ELMs. We observe that the premature excitation of ELMs by means of pellet injection is caused by a helical perturbation described by a toroidal mode number of n = 1. In accordance with experimental observations, the pellet-triggered ELMs show reduced thermal energy losses and narrower divertor wetted area with respect to spontaneous ELMs. The peak divertor energy fluency is seen to decrease when ELMs are triggered by pellets injected earlier during the pedestal build-up.

References in corpus (8)

• The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas
• Non-linear modeling of the plasma response to RMPs in ASDEX Upgrade
• Nonlinear excitation of low-n harmonics in reduced magnetohydrodynamic simulations of edge-localized modes
• Non-linear extended MHD simulations of type-I edge localised mode cycles in ASDEX Upgrade and their underlying triggering mechanism
• Reduced-MHD Simulations of Toroidally and Poloidally Localized ELMs
• Non-linear modeling of the threshold between ELM mitigation and ELM suppression by Resonant Magnetic Perturbations in ASDEX Upgrade
• First predictive simulations for deuterium shattered pellet injection in ASDEX Upgrade
• Transition from no-ELM response to pellet ELM triggering during pedestal build-up -- insights from extended MHD simulations

Cited by in corpus (6)

• The JOREK non-linear extended MHD code and applications to large-scale instabilities and their control in magnetically confined fusion plasmas
• MHD simulations of small ELMs at low triangularity in ASDEX Upgrade
• Magnetic flutter effect on validated edge turbulence simulations
• MHD simulations of formation, sustainment and loss of Quiescent H-mode in the all-tungsten ASDEX Upgrade
• Probing non-linear MHD stability of the EDA H-mode in ASDEX Upgrade
• Electromagnetic turbulence simulation of tokamak edge plasma dynamics and divertor heat load during thermal quench