Experimental conditions to suppress edge localised modes by magnetic perturbations in the ASDEX Upgrade tokamak

Abstract

Access conditions for full suppression of Edge Localised Modes (ELMs) by Magnetic Perturbations (MP) in low density high confinement mode (H-mode) plasmas are studied in the ASDEX Upgrade tokamak. The main empirical requirements for full ELM suppression in our experiments are: 1. The poloidal spectrum of the MP must be aligned for best plasma response from weakly stable kink-modes, which amplify the perturbation, 2. The plasma edge density must be below a critical value, $3.3\times 10^{19}$~m${}^{-3}$. The edge collisionality is in the range ${\nu }_i^{\ast }=0.15-0.42$ (ions) and ${\nu }_e^{\ast }=0.15-0.25$ (electrons). However, our data does not show that the edge collisionality is the critical parameter that governs access to ELM suppression. 3. The pedestal pressure must be kept sufficiently low to avoid destabilisation of small ELMs. This requirement implies a systematic reduction of pedestal pressure of typically 30\% compared to unmitigated ELMy H-mode in otherwise similar plasmas. 4. The edge safety factor $q_{95}$ lies within a certain window. Within the range probed so far, $q_{95}=3.5-4.2$, one such window, $q_{95}=3.57-3.95$ has been identified. Within the range of plasma rotation encountered so far, no apparent threshold of plasma rotation for ELM suppression is found. This includes cases with large cross field electron flow in the entire pedestal region, for which two-fluid MHD models predict that the resistive plasma response to the applied MP is shielded.

References in corpus (4)

• Effect of resonant magnetic perturbations on low collisionality discharges in MAST and a comparison with ASDEX Upgrade
• Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium
• Field-line localized destabilization of ballooning modes in 3D tokamaks
• Three dimensional boundary displacement due to stable ideal kink modes excited by external n=2 magnetic perturbations

Cited by in corpus (10)

• Wide operational windows of edge-localized mode suppression by resonant magnetic perturbations in the DIII-D tokamak
• The Role of Edge Resonant Magnetic Perturbations in Edge-Localized-Mode Suppression and Density Pump-out in low-collisionality DIII-D Plasmas
• Robust avoidance of edge-localized modes alongside gradient formation in the negative triangularity tokamak edge
• Plasma Performance and Operational Space without ELMs in DIII-D
• Non-linear modeling of the threshold between ELM mitigation and ELM suppression by Resonant Magnetic Perturbations in ASDEX Upgrade
• Nonlinear modeling of the scaling law for the m/n=3/2 error field penetration threshold
• FLARE: field line analysis and reconstruction for 3D plasma boundary modeling
• Operational Space and Plasma Performance with an RMP-ELM Suppressed Edge
• Heuristic predictions of RMP configurations for ELM suppression in ITER burning plasmas and their impact on divertor performance
• Plasma response to resonant magnetic perturbations near rotation zero-crossing in low torque plasmas