Modelling plasma response to RMP fields in ASDEX Upgrade with varying edge safety factor and triangularity

Abstract

Toroidal computations are performed using the MARS-F code [Liu Y Q et al 2000 Phys.Plasmas 7 3681], in order to understand correlations between the plasma response and the observed mitigation of the edge localized modes (ELM) using resonant magnetic perturbation fields in ASDEX Upgrade. In particular, systematic numerical scans of the edge safety factor reveal that the amplitude of the resonant poloidal harmonic of the response radial magnetic field near the plasma edge, as well as the plasma radial displacement near the X-point, can serve as good indicators for predicting the optimal toroidal phasing between the upper and lower rows of coils in ASDEX Upgrade. The optimal coil phasing scales roughly linearly with the edge safety factor 95 q , for various choices of the toroidal mode number n=1-4 of the coil configuration. The optimal coil phasing is also predicted to vary with the upper triangularity of the plasma shape in ASDEX Upgrade. Furthermore, multiple resonance effects of the plasma response, with continuously varying 95 q , are computationally observed and investigated.

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

“…Defining the coil phasing that maximizes b 1 res as the "optimal" coil phasing, we find 60 shift in the optimal phasing between the total response field and the vacuum field, for the dominant n ¼ 1 component. This 60 phase shift is close to what has been found for ASDEX Upgrade plasmas [10][11][12] as well.…”

“…In particular, the fluid model predicted optimal coil phasing, which maximizes the edge-peeling response, agrees well with the best achievable ELM mitigation in experiments. 33 This is confirmed by MARS-F, [10][11][12] NEMEC, 4 and JOREK 13 computations. In particular, systematic scans with varying edge safety factor 12,37 as well as plasma pressure 37 yield simple analytic fitting formulas for the optimal coil phasing, with varying plasma conditions.…”

“…As has been shown in the previous MARS-F modeling for MAST, 7 ASDEX Upgrade, [10][11][12] and EAST, 14 ELM mitigation is closely correlated to the edge-peeling response, which often manifests itself as pronounced plasma displacement near the X-point. 19 We examine here these aspects for the HL-2A case, with results summarized in Figs.…”

“…Extensive MARS-F modelling has been performed for MAST, 7 ASDEX Upgrade, [10][11][12] and EAST. 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.…”

“…Extensive modelling efforts have been devoted to understand and to interpret ELM control experiments. Most of the modelling work has been carried out for individual devices, for example, MAST, 7 DIII-D, 8,9 ASDEX Upgrade, [10][11][12][13] EAST, 14 and ITER. 7,[15][16][17] These activities were also reported in recent review articles.…”