Numerical study of the resonant magnetic perturbations for Type I edge localized modes control in ITER

Abstract

A number of possible designs of external and in-vessel coils generating resonant magnetic perturbations (RMPs) for Type I edge localized modes (ELMs) control in ITER are analysed for the reference scenarios (H-mode, Hybrid and Steady-State) taking into account physical, technical and spatial constraints. The level of stochasticity (Chirikov parameter ∼1 at ψ1/2 ∼ 0.95) generated by the I-coils in the DIII-D experiments on ELMs suppression was taken as a reference. Designs with a toroidal symmetry n = 3 were considered to avoid lower n numbers producing larger central islands, a potential trigger of MHD instabilities. The evaluation of RMP coils designs is done with respect to the RMPs spectrum that should produce enough edge ergodisation and minimum central perturbations at minimum current. The proposed designs include in-vessel, mid-ports and external coils. Changes in the equilibrium due to changes in the internal inductance l i, the poloidal beta βp and the edge magnetic shear in a reasonable range for ITER scenarios were demonstrated to have a small effect on the edge ergodisation. Present estimations were done without margins and for vacuum fields neglecting plasma response on RMPs. The validity of the vacuum approach was estimated analytically in the visco-resistive linear response regime using [1]. The typical radial magnetic field amplitudes produced by RMP coils in DIII-D and ITER are an order of magnitude or slightly above the critical values for the ‘downward’ bifurcation to the reconnected stage indicating the possibility of the islands formation in the pedestal region. Central islands (from the top of the pedestal) are expected to be screened.

Non-linear magnetohydrodynamic modeling of plasma response to resonant magnetic perturbations

“…The application of the RMPs is modeled by a change in boundary conditions for the magnetic flux perturbation. The vacuum RMP spectrum is previously calculated with the ERGOS code [22] and applied as boundary conditions of the computational domain for the magnetic flux perturbation. RMPs are progressively switched on in time: the amplitude of the perturbation is gradually increased in the typical timescale t ∼ 1000t A .…”

Mechanism of Edge Localized Mode Mitigation by Resonant Magnetic Perturbations

“…Recently the application of Resonant Magnetic Perturbations (RMPs) demonstrated the possibility of total ELMs suppression or strong mitigation of their size [3][4][5][6][7][8][9], motivating the use of this method in ITER [1]. In the last decade, the non-linear MHD theory and modeling have made a significant progress to refine the understanding of ELM [10][11][12][13][14] and RMP [15][16][17][18][19][20] physics. However the understanding of RMP interaction with ELMs is still missing and was not modeled so far, motivating work we are presenting here.…”

“…The JOREK model used here includes two-fluid diamagnetic effects important in the pedestal region and is described in details in [18]. The realistic JET pulse #77329 parameters used as in [17,18,19] 7 , which for numerical reasons is lower compared to the experimental value (S=10 9 ). In the typical JOREK run initially the equilibrium with flows is obtained for the toroidal harmonic n=0 (axisymmetric component) on a time scale of ~1ms [18].…”

“…After that, for ELMs modelling, other harmonics are initialized in plasma at "noise" level (~10 -25 ). In the case of RMPs vacuum amplitude for corresponding harmonic (here n=2 from EFCC [6,17,19]) is set at the boundary and increased in time until the stationary conditions are reached [18], resulting in a 3D equilibrium, then other harmonics were initialized to study interaction of ELMs with RMPs. 2.…”

“…The JOREK model used here includes two-fluid diamagnetic effects important in the pedestal region and is described in details in [18]. The realistic JET pulse #77329 parameters used as in [17,18,19]: R 0 =2.9m, a=0.89m, B tor =1.8T, q 95 =3.8. The density and…”