Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements

Abstract

The multiphase simulations are conducted with the kinetic-magnetohydrodynamics hybrid code MEGA to investigate the spatial and the velocity distributions of lost fast ions due to the Alfvén eigenmode (AE) bursts in the Large Helical Device plasmas. It is found that fast ions are lost along the divertor region with helical symmetry both before and during the AE burst except for the promptly lost particles. On the other hand, several peaks are present in the spatial distribution of lost fast ions along the divertor region. These peaks along the divertor region can be attributed to the deviation of the fast-ion orbits from the magnetic surfaces due to the grad-B and the curvature drifts. For comparison with the velocity distribution of lost fast ions measured by the fast-ion loss detector (FILD), the ‘numerical FILD’ which solves the Newton–Lorentz equation is constructed in the MEGA code. The velocity distribution of lost fast ions detected by the numerical FILD during AE burst is in good qualitative agreement with the experimental FILD measurements. During the AE burst, fast ions with high energy (100–180 keV) are detected by the numerical FILD, while co-going fast ions lost to the divertor region are the particles with energy lower than 50 keV.

Precession drift reversal and rapid transport of trapped energetic particles due to an energetic particle driven instability in the Large Helical Device

“…MEGA has been successfully used to study wave-particle interactions in multiple tokamaks [22][23][24][25][26] as well as the LHD. [27][28][29][30] In this work, an m=n ¼ 1=1 EIC mode is not observed, which may be due to the fixed boundary condition chosen or other effects that will be investigated in a later study. This Letter is instead focused on the destabilization of an m=n ¼ 2=1 mode, closer to the plasma center than the EIC, by an anisotropic population of energetic particles in a high-performance deuterium LHD plasma.…”

A study of beam ion and deuterium–deuterium fusion-born triton transports due to energetic particle-driven magnetohydrodynamic instability in the large helical device deuterium plasmas

“…A study of energetic ion loss due to the toroidal Alfvén eigenmode showed that the dominant loss process changed according to the plasma center position due to the change of energetic ion orbit and eigenfunction of the toroidal Alfvén eigenmode [22]. Comparing experimental results and the numerical simulation results revealed the loss process of beam ions due to the Alfvén eigenmode [23,24].…”