Simulation study of fast ion losses associated with the rotating n = 1 resonant magnetic perturbations in KSTAR

Abstract

This paper describes a simulation framework for testing the fast ion loss mechanism associated with the experimentally observed beam ion losses when an externally applied toroidally rotating perturbed magnetic field is used to control edge localized modes in the KSTAR tokamak. The simulations reproduce the key qualitative features of neutral beam injection (NBI) ion detection by a fast ion loss detector. The NBI ion losses in the simulation mainly occur for passing particles due to orbit stochastization, which is caused by orbit resonance with the 3D field perturbations. The relative toroidal angle of NBI ion deposition to the orbit island determines the radial path of the particles between confinement or loss. The fast ion loss quantity depends on the toroidal angle rotation of the 3D field with respect to the beam deposition position. The averaged transport of toroidal canonical angular momentum reveals that linear and nonlinear resonance of the NBI ions within the 3D field are the main factors determining fast ion transport and loss.

Tailoring resonant magnetic perturbation to optimize fast-ion confinement during ELM control in KSTAR

“…This breaking of the KAM surface at inner integral q eff indicates that KAM surface breaking at these regions leads to more fast ion losses. The difference in fast ion loss in figure 12 and KAM surface in figure 13 at 0.7B pert clearly indicates a correlation between the threshold in the additional fast ion losses and the threshold for KAM surface breaking as discussed in [21]. Also note that the magnetic field line looks slightly different with 0.3B pert at more edge regions, q eff > 3.5, as shown in figures 13(d)-(f ), but this leads to similar fast ion losses as shown in figure 12.…”

“…This result suggests that reducing the core resonant field can positively impact the overall confinement of fast ions in the plasma. Figure 8(c) also compares the toroidal angle dependence of fast ion losses, as fast ion losses due to RMPs is known to have a strong toroidal angle dependence [13,14,21]. Here, the toroidal phase of midplane coils, the closest 3D coils to the plasma boundary, is identical for all three cases, and the poloidal spectra are modified using the toroidal phase of the upper and lower coil rows.…”

“…The NuBDeC code calculates the deposition of fast ions by neutral beam injection (NBI) and follows the guiding center orbits of the fast ions. NuBDeC has the capability to calculate fast particle loss with a perturbed magnetic field calculated by IPEC code, as shown in [21]. Therefore, the outputs from IPEC are directly plugged into the NuBDeC to estimate fast ion losses due to the different poloidal spectra of 3D fields.…”

Application of non-axisymmetric magnetic field for control of Alfvén eigenmodes in KSTAR

“…The fast ion response to the phase-sweeping 3D field can be determined by the resonant and/or non-resonant characteristics of the applied field that periodically changes its phase and interactions with the fast particles. We numerically analyze the 3D field effects on the fast ion prompt loss and the phase-space distribution utilizing the NuBDeC code [30]. The NuBDeC code computes the fast ion motions from the birth by NBI to the prompt loss induced by the 3D field.…”