Numerical study of neutral beam injection prompt loss at KSTAR poloidal limiters

Abstract

We use a newly developed simulation tool to numerically study fast-ion loading on plasma-facing components (PFCs) at the Korea Superconducting Tokamak Advanced Research facility in the high-poloidal-β plasma operation regime. The new code can calculate neutral beam ionization and follow the guiding center orbit of ionized particles. The results of the simulation indicate that fast ions ionized in the high-field side drift out and strike the PFCs as they rotate poloidally. Momentum projection onto a phase space defined by canonical toroidal angular momentum and magnetic moment leads to a simple criterion to avoid fast-ion loading on poloidal limiters (PLs), which are PFCs that are toroidally localized on the low-field side. Control of fast-ion loss is examined by varying the plasma current and plasma boundary. A larger plasma current and inner shifting of the outer plasma boundary is predicted to substantially reduce fast-ion loading on the PLs. The proposed phase-space criterion is qualitatively consistent with the results of the simulation of fast-ion control.

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

“…Simulations were performed with the NuBDeC code [3] to calculate the KSTAR NBI ion deposition and the beam ion guiding center orbits. A detailed description of beam deposition process and ion orbit following calculation in axisymmetric tokamak can be found at [3].…”

“…Simulations were performed with the NuBDeC code [3] to calculate the KSTAR NBI ion deposition and the beam ion guiding center orbits. A detailed description of beam deposition process and ion orbit following calculation in axisymmetric tokamak can be found at [3]. The updated code has the capability to calculate the orbit evolution with a perturbed magnetic field, e.g., from resonant magnetic perturbations, whereas the previous version only included an unperturbed, axis-symmetric equilibrium magnetic field.…”

“…The aim of KSTAR is to demonstrate steady-state operation under long-pulse scenarios with 400-600 kA and to achieve a safety factor q min of greater than 1. The high-q profile induces significant drift in fast ions and causes plasma-facing components to overheat under the NBI ions in KSTAR [3]. This limits the plasma operation parameter range and can damage plasma-facing components during long-pulse operation.…”

“…Overlapping orbit islands achieved by perturbation amplitudes greater than the Chirikov criterion can produce a stochastic path in fast ions and cause the transport threshold of passing particles to be exceeded. Therefore, stochastic transport is an orbit-loss mechanism of large-drift NBI ions, such as those in KSTAR [3].…”

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

“…Figures 6(a), (b) and (e) show simulated total #26026 to PFCs and loss to the poloidal limiters (PL1, PL2, PL3) at the different toroidal locations at ϕ = 145 • , 170 • , and 190 • . A poloidal location of poloidal limiter is shown in figure 1(c), and the more precise location of PL1, PL2, and PL3 are described in [20]. The simulations show that #26026 without the 3D field effect are small and almost similar for the two cases.…”