Mechanisms of Edge-Localized-Mode Mitigation by External-Magnetic-Field Perturbations

Abstract

Particle and energy transport in the tokamak edge transport barrier is analyzed in the presence of magnetic field perturbations from external resonant coils. In recent experiments such coils have been verified as an effective tool for mitigation of the edge-localized modes of type I. The observed reduction of the density in plasmas of low collisionality is explained by the generation of charged particle flows along perturbed field lines. The increase of the electron and ion temperatures in the barrier is interpreted by the reduction of perpendicular neoclassical transport with decreasing density and nonlocality of parallel heat transport. The found modification of the pressure gradient implies the stabilization of ballooning-peeling MHD modes responsible for type I ELMs.

Plasma transport in stochastic magnetic field caused by vacuum resonant magnetic perturbations at diverted tokamak edge

“…Parallel electron mobility in the radial direction alongB r /B, as usual, is adjusted by E r to yield the self-consistent E r and the ion/electron losses. with the reductution effect by the radial electric field included [10]. The convective part is non-negligible compared to the conductive part, unlike the model used in the R-R theory.…”

“…Figure 1 displays the plasma profiles for DIII-D discharge 126006 versus the poloidal magnetic flux ψ N , a radial coordinate normalized to be 0 at the magnetic axis and 1 at the magnetic separatrix. Analytic and fluid modelings have used the baseline ingredients of R-R theory for the electron heat transport in stochastic magnetic field with only incomplete understanding of the plasma transport mechanisms in stochastic magnetic field [10][11][12][13][14]. Incomplete understanding of the plasma transport mechanisms in stochastic magnetic field in toroidal confinement geometry makes the ELM control by RMP coils in future tokamak reactors uncertain.…”

Three-dimensional edge transport simulations for DIII-D plasmas with resonant magnetic perturbations

“…In particular the impact on the pressure gradient in the edge transport barrier is of great interest, because this is correlated with the stabilization of peeling-balloning MHD modes considered as the cause of ELMs [8]. In present edge transport models for RMP ELM control scenarios [9,10] only the magnetic flux surface averaged effects of RMPs are considered. There is, however, strong experimental evidence, e.g.…”

Free energy minimization approach to penetration of resonant magnetic perturbations in tokamaks

“…[1][2][3][4] Numerous theoretical studies have been performed in order to describe those experiments and specific features of particle and energy transport in the presence of RMPs. [5][6][7][8][9][10][11][12][13][14] Diverse mechanisms of the RMP effect on transport processes revealed in these studies rely significantly on the level of the perturbation amplitude in the edge plasma. Thus, in many investigations [13][14][15][16][17] the vacuum approximation considering the total magnetic field in the plasma region as a sum of the axisymmetric confinement field and the vacuum field induced by the external coils has been applied.…”