Resonant effects on the loss of energetic trapped ions induced by low-n resonant magnetic perturbations

Abstract

The fast ion dynamics and the associated loss channels under resonant magnetic perturbation (RMP) fields are investigated numerically with newly upgraded Monte-Carlo code ORBIT-RF. Special attention is paid to the effect of low-n () perturbations on the confinement of energetic trapped ions in an equilibrium from EAST experiments. Here, n donates the toroidal mode number. It is found that the dominant loss mechanism under n = 2 RMP is essentially different from that under n = 1 RMP. For n = 2 RMP, the enhanced losses are mainly due to the single resonance with . Here, and are, respectively, the precession and bounce frequencies. For n = 1 RMP, the losses are mainly due to orbital stochasticity near the trapped-passing boundary, which is mainly promoted by the nonlinear resonances. It is found that the loss fraction has a sine-like dependence on the phase difference between the upper and lower coil currents under both n = 1 and n = 2 RMPs, which suggests the possibility of active control of fast ion profile by designing the spectrum. The loss rate under n = 2 RMP shows a linear dependence on the perturbation amplitude, while the loss rate under n = 1 RMP shows a quadratic dependence. The results here highlight the importance of nonlinear resonances in fast ion confinement under RMP, in addition to that of linear resonances frequently emphasized before.

Role of the edge electric field in the resonant mode-particle interactions and the formation of transport barriers in toroidal plasmas

“…In particular, higher energy particles experience significant radial drifts across the magnetic field lines, and their trajectory only partially resides in the vicinity of a magnetic island, suggesting that the chaoticity of the orbits cannot be directly derived from the chaoticity of the magnetic field lines. This is not the case for low-energy particles, whose radial drift is considerably smaller, and hence, particle trajectories follow the magnetic field lines, inheriting its chaoticity (Cambon et al 2014;He et al 2019He et al , 2020Moges et al 2024).…”

Effects of resonant magnetic perturbations on neutral beam heating in a tokamak

“…( 4)], which can be inferred from Poincare sections of magnetic field lines. Figure (13) shows the Poincare plots of magnetic field line for RMPs of ∆Φ = 0 and ∆Φ = π. The results indicate that magnetic islands for RMP of ∆Φ = 0 are wider than those of ∆Φ = π.…”

“…EAST is equipped with RMP coils which are designed for the control of edge localized modes (ELMs) 9,10 . This coils turn out to also have effects on the transport of neutral beam fast ions [11][12][13][14][15] . The effects of RMPs on fast ion transport and loss have been extensively investigated on AUG [16][17][18] , KSTAR 19 , DIII-D 20,21 , and MAST 22 tokamaks.…”

Roles of primary and sideband resonances in the confinement of energetic passing ions under resonant magnetic perturbations

“…A series of experimental observations in ASDEX Upgrade [9][10][11], KSTAR [10,12], DIII-D [13,14] and MAST [15] reveal that RMP can induce extra losses of ions from neutral beam injection (NBI). Meanwhile, numerical simulations based on orbit-following calculations have been widely used to reproduce experimental results and to study related loss mechanisms [9,[11][12][13][14][15][16][17][18][19][20][21]. For ITER plasmas, some predictive simulation results [22][23][24][25][26] suggest that RMP fields can induce considerable losses of fast ions, especially beam ions.…”

“…In tokamaks, there are two basic types of particles, trapped and passing particles. In our recent study [21], efforts have been made to clarify some important effects of RMP on the confinement of trapped ions. In this paper, we focus on passing ions.…”