Toroidal modeling of runaway electron loss due to 3D fields in ITER

Abstract

Mitigation of runaway electrons (REs) by three-dimensional (3-D) magnetic field perturbations is numerically investigated for the ITER 15 MA baseline D-T scenario, utilizing the MARS-F code [Liu et al Phys. Plasmas 7 3681] with a drift orbit test particle tracing module. Considered are two types of 3-D fields: the n=3 (n is the toroidal mode number) resonant magnetic perturbation (RMP) utilized for the purpose of controlling the edge localized modes in ITER, and perturbations generated by the n=1 magneto-hydrodynamic (MHD) instabilities in a post-disruption plasma. The RMP field, applied to a pre-disruption plasma, is found to be moderately effective in mitigating the RE seeds in ITER when vacuum field model is assumed. Up to ~40% loss fraction is possible at 90 kA-turn coil current. The mitigation efficiency is however substantially reduced, down to less than 5%, when the plasma response is taken into account. This is due to strong screening of the resonant magnetic field components by the plasma response resulting in much less field line stochasticity. On the other hand, the MARS-F modeling, based on the DINA-simulated post-disruption equilibria, shows that the n=1 resistive kink instabilities develop in these plasmas, as the edge safety factor qa evolves and drops below integer numbers. RE mitigation by these MHD instabilities is sensitive to the eigenmode structure. The best mitigation is achieved as qa drops below 3, when a global kink instability occurs that encompasses both internal and external components. This global instability is found to be capable of mitigating over 80% MeV-level passing RE orbits at a field perturbation |delta B|/B0 that is comparable to that observed in DIII-D experiments, and full mitigation if the perturbation amplitude is doubled. The ``wetted" area on the ITER limiting surface, due to MHD instability induced RE loss, generally increases with the perturbation amplitude (together with increasing loss fraction). At the highest perturbation level assumed in this study, the wetted area reaches ~60% of the total limiting surface area. The lost RE orbits mainly strike the outer divertor region of the limiting surface, with some fraction also hitting a wide area along the inboard side of the surface.

Runaway electron deconfinement in SPARC and DIII-D by a passive 3D coil

“…Experiments aimed at mitigating tokamak disruptions with massive material injection (gas or pellets) have long sought unsuccessfully to exceed the socalled Rosenbluth density to maintain E < E crit even at post-TQ temperatures [3][4][5]. Injection of either high-Z (Ne, Ar, Kr, Xe) [6,7] or low-Z (He, D 2 ) [7,8] material into an existing RE beam has also been pursued, with D 2 injection showing strong promise experimentally for benign termination of a RE beam by a kink instability, supported by extendedmagnetohydrodynamic (MHD) modeling [9][10][11], which has been extended to ITER scenarios [12]. Strategies to prevent the formation of a mature RE beam involve enhancing transport of the seed REs in physical or momentum space, e.g., by stochastic magnetic fields [13][14][15][16][17][18] or wave-particle interactions [19,20], to produce a loss rate that exceeds the avalanche growth rate.…”

Stability of a weakly collisional plasma with runaway electrons

“…[6] we expect the electron inertia terms in the generalized Ohm's law to become relevant in the sublayer physics found in this regime. A further step of this work will be to consider multiple helicity reconnection modes introducing magnetic field lines stochasticity expected to play a significant role in the runaway electron dispersion [14,15].…”

Electron modelling in conjunction witch vacuum modelling

“…In the horizon of scientific research on the problems of simulation of electrons and electron-related processes, it is worth noting the studies by C. Lamy (on the possibility of using artificial neural networks for modelling non-local electron transport in plasma) [1], B. Tang (on numerical modelling of the processes of suprathermal electron transport in the solar wind) [2], X. An (on modelling the effects of bound electrons in the process of model studies of particles in a cell) [3], Y. Liu (on toroid modelling of electron loss processes flowing out of a 3D field in the organisation of research in the international experimental thermonuclear reactor (ITER)) [4], X. Li (on modelling the processes of acceleration and electron transfer in the early pulsed phase of a solar flare) [5], "Modelling of non-local electron transport in laser-driven double-ablation fronts" [6], "Relaxation of electron beams/strahls in solar outflows: observations vs. modelling" (on the correlated analysis of the results of modelling and full-scale measurements of electron beam/strahl relaxation processes in solar flows) [7], H. Funaba (on the study of the Thomson scattering effect in modelling and estimating electron temperature) [8], D. Vatansever et al (on modelling surfaces that emit electrons when boundary layers are immersed in plasma) [9], V. Lazurik (on the investigation of semi-empirical models of electron beam control in radiation technologies) [10], O. Linder (on self-matching modelling of electron run-up during breakdowns in Tokamak (ITER)) [11], L. Adhikari (on modelling the process of heating protons and electrons in a fast solar wind) [12], M. Wibowo (on modelling the dynamics of ultra-fast electrons in strong magnetic fields using real-time electronic structure methods) [13], Y. Huang (on modelling strong electron heating by radio frequency waves at EAST) [14], Z. Wang (on real-time modelling and estimation of the total electron content in the vertical global ionosphere using hourly IGS data) [15]. When analysing these specialised publications, it was found that in modern physics, electron models only describe its properties.…”