MHD simulations of formation, sustainment and loss of quiescent H-mode in the all-tungsten ASDEX Upgrade

Nuclear Fushion

article

Lorenz Meier¹  Matthias Hoelzl²  Andres Cathey²  Guido Huijsmans¹  Eleonora Viezzer⁴  Mike Dunne²  Jan van Dijk¹  Diego José Cruz Zabala⁴  Karl Lackner²  Sibylle Günter² 

[1] Eindhoven University of Technology;Max Planck Institute for Plasma Physics;CEA;Department of Atomic, Molecular and Nuclear Physics, University of Seville

关键词: edge turbulence;    thermal quench;    divertor heat load;   

DOI  :  10.1088/1741-4326/acd5e2

来源: Institute of Physics Publishing Ltd.

【 摘 要 】

Periodic edge localized modes (ELMs) are the non-linear consequences of pressure-gradient-driven ballooning modes and current-driven peeling modes becoming unstable in the pedestal region of high confinement fusion plasmas. In future tokamaks like ITER, large ELMs are foreseen to severely affect the lifetime of wall components as they transiently deposit large amounts of heat onto a narrow region at the divertor targets. Several strategies exist for avoidance, suppression, or mitigation of these instabilities, such as the naturally ELM-free quiescent H-mode (QH-mode). In the present article, an ASDEX Upgrade (AUG) equilibrium that features a QH-mode is investigated through non-linear extended magneto-hydrodynamic simulations covering the dynamics over tens of milliseconds. The equilibrium is close to the ideal peeling limit and non-linearly develops saturated modes at the edge of the plasma. A dominant toroidal mode number ofn  = 1 is found, for which the characteristic features of the edge harmonic oscillation are recovered. The saturated modes contribute to heat and particle transport preventing pedestal build-up to the ELM triggering threshold. The non-linear dynamics of the mode, in particular its interaction with the evolution of the edge safety factor, are studied, and suggest a possible new saturation mechanism for the QH-mode. The simulations show good qualitative and quantitative agreement with experiments in AUG. In particular, the processes leading to the termination of QH-mode above a density threshold are studied, which results in the transition into an ELM regime. In the vicinity of this threshold, limit cycle oscillations are observed.

【 授权许可】

Unknown