ELM control with RMP: plasma response models and the role of edge peeling response

Abstract

Resonant magnetic perturbations (RMP) have extensively been demonstrated as a plausible technique for mitigating or suppressing large edge localized modes (ELMs). Associated with this is a substantial amount of theory and modelling efforts during recent years. Various models describing the plasma response to the RMP fields have been proposed in the literature, and are briefly reviewed in this work. Despite their simplicity, linear response models can provide alternative criteria, than the vacuum field based criteria, for guiding the choice of the coil configurations to achieve the best control of ELMs. The role of the edge peeling response to the RMP fields is illustrated as a key indicator for the ELM mitigation in low collisionality plasmas, in various tokamak devices.

Comparative investigation of ELM control based on toroidal modelling of plasma response to RMP fields

“…A closer analysis reveals that the large X-point displacement is a sufficient but not a necessary condition when the edgepeeling response is dominant-a more general condition is the weak equilibrium poloidal field along the certain poloidal angle of the plasma surface. 19 The edge-peeling response criterion is particularly useful in providing guidance for optimization of the RMP coil phasing, as has been demonstrated in MAST, ASDEX Upgrade, and EAST in the previous work, and in the detailed modelling for HL-2A in this study. Extensive modeling has also shown that the optimal coil phasing depends on the plasma conditions, in particular, on the edge-q value (q 95 ) as well as on the plasma pressure.…”

“…14 All the modelling results, in comparison with the corresponding experimental observations, so far point to the important role played by the edge-peeling response for achieving the best ELM mitigation. 19 The edge-peeling response, which was first identified in modelling of the JET experiments, 34 is found to be closely correlated to the pronounced plasma surface displacement near the X-point. On the contrary, the other type of the plasma response-the core-kink response-often causes large plasma displacement near the outboard mid-plane, due to the ballooning effect.…”

“…19 The plasma surface displacements, as functions of the poloidal angle, are plotted and compared in Fig. 11 for the two ASDEX Upgrade equilibria with low and high upper triangularity shaping.…”

“…7,[15][16][17] These activities were also reported in recent review articles. 18,19 In this work, we report some of the recent multimachine, comparative modelling results on the ELM control experiments utilizing the RMP fields. More specifically, we focus on the toroidal computation of the plasma response to RMP fields.…”

“…19 We examine here these aspects for the HL-2A case, with results summarized in Figs. 3 and 4, where we again scan the coil phasing D/.…”