Linear ideal MHD predictions forn= 2 non-axisymmetric magnetic perturbations on DIII-D

Abstract

An extensive examination of the plasma response to dominantly n = 2 non-axisymmetric magnetic perturbations (MPs) on the DIII-D tokamak shows the potential to control 3D field interactions by varying the poloidal spectrum of the radial magnetic field. The plasma response is calculated as a function of the applied magnetic field structure and plasma parameters, using the linear magnetohydrodynamic code MARS-F (Liu et al 2000 Phys. Plasmas 7 3681). The ideal, single fluid plasma response is decomposed into two main components: a local pitch-resonant response occurring at rational magnetic flux surfaces, and a global kink response. The efficiency with which the field couples to the total plasma response is determined by the safety factor and the structure of the applied field. In many cases, control of the applied field has a more significant effect than control of plasma parameters, which is of particular interest since it can be modified at will throughout a shot to achieve a desired effect. The presence of toroidal harmonics, other than the dominant n = 2 component, is examined revealing a significant n = 4 component in the perturbations applied by the DIII-D MP coils; however, modeling shows the plasma responses to n = 4 perturbations are substantially smaller than the dominant n = 2 responses in most situations.

Plasma response measurements of external magnetic perturbations using electron cyclotron emission and comparisons to 3D ideal MHD equilibrium

“…Both calculations show a kink response situated at |m| > |nq|, which amplifies the field perturbation. This has been reported previously [15,17,65,61] and has also been synth. data linear fit ECE-I ECE-I, optically thin Figure 18.…”

“…In DIII-D, for example, this is not the case. It has 6 saddle coils in each row and the aliasing effect causes an n = 4 component [61]. The combination of Ampere's law j = ∇ × B and the plasma equilibrium ∇ p = j × B introduces a non-linear (≈ B 2 ) behavior due to the plasma response.…”

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

“…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.…”

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

“…Despite significant efforts during recent years [8][9][10][11][12][13][14][15][16][17][18][19], theoretical understanding of the ELM control physics with RMP fields is so far incomplete. It is, however, well established now that the plasma response plays a significant role in the ELM mitigation, possibly also in the ELM suppression.…”