First three-dimensional edge plasma transport simulations with magnetic perturbations induced by lower hybrid waves on EAST

Abstract

Recent experiments from the Experimental Advanced Superconducting Tokamak (EAST) show that lower hybrid waves (LHWs) can profoundly change the magnetic topology by inducing helical current filaments flowing along magnetic field lines in the scrape-off layer. Here, it is investigated for the first time how these magnetic perturbations caused by LHWs affect the edge plasma transport utilizing the three-dimensional Monte Carlo code EMC3-EIRENE, both in double-null and single-null configurations. The 3D magnetic topology structure is reflected in the plasma properties, due to much stronger parallel field transport compared with cross field diffusion. Good qualitative agreements between simulation results and experimental data from various edge diagnostics demonstrate that the EMC3-EIRENE code now is capable of taking into account the LHW-induced magnetic perturbation fields with both physical and geometrical effects being considered. Combined with experimental observations, the simulation results strongly support that total current amplitude of LHWinduced filaments increases with an increase in LHW input power. It can further deepen the penetration depth of the additional transport channel by extending the stochastic edge layer, and influence the ratio of heat (or particle) flux between split striated and original strike line on divertor targets. The 3D simulation results also indicate that the additional plasma transport channel induced by LHWs can significantly cause the redistribution of heat load between inner and outer divertor targets, which could not be found by the field line tracing method in previous works.

Mechanism of the active divertor flux control by the supersonic-molecular-beam-injection with lower hybrid wave-induced magnetic perturbations on the EAST tokamak

“…The total current of LHWinduced filaments is 2 kA with a distance ~28 ± 8 mm to the last closed flux surface (LCFS) at the mid-plane in front of the LHW antenna. The formation of the filaments is the same with that in reference [21]. The positions and pitch angles of the filaments show a good agreement with the helical radiation belts observed by the visible camera.…”

“…EMC3 solves a set of Braginskii fluid equations formulated in a Fokker-Planck scheme by using the Monte-Carlo method, while the EIRENE code is for multi-species Boltzmann equations with chemical processes, based on conventional Monte-Carlo particle transport algorithms. After continuous improvements and upgrade in the past years, EMC3-EIRENE now is capable of taking into account the LHW-induced magnetic perturbations with both the physical and geometrical effects being considered [21].…”

Edge turbulence characteristics and transport during the ELM mitigation with n = 1 resonant magnetic perturbation on EAST

“…In order to evaluate the radial particle flux across the LCFS, it is assumed that the cross-field particle flux is homogeneous on the same flux surface. As we know, the radial transport favors the low-field side (LFS) in tokamaks due to the bad curvature [49], and the edge transport is asymmetrical toroidally under magnetic perturbations [50,51]. As a result, this assumption will lead to some uncertainties to the particle exhaust across the LCFS.…”

Equilibrium effects on the structure of island divertor and its impact on the divertor heat flux distribution in Wendelstein 7-X

“…Recently, applications of three-dimensional (3D) magnetic topologies for controlling the edge plasma transport, instabilities, and plasma-wall interactions have attracted substantial attention in magnetic confinement fusion research [1][2][3][4]. The strong correlation between 3D magnetic topologies and divertor heat flux deposition patterns has been demonstrated and investigated, not only in tokamaks with the application of symmetry-breaking magnetic perturbation fields [5][6][7][8][9][10][11][12] but also in stellarators with intrinsic 3D nonaxisymmetric magnetic fields [13][14][15][16][17].…”