Particle Orbit Analysis under the Ion Cyclotron Range of Frequency Heating in the Large Helical Device

Abstract

Particles under the influence of the ion cyclotron range of frequency (ICRF) electromagnetic field were analyzed in the large helical device (LHD) by numerically solving the equation of motion instead of the guiding-center equation. Behaviors of the ICRF-heated particles in three cases of slowing-down by thermal electrons were compared. We also compared the characteristics of the ICRF-heated particles in the standard magnetic configuration (Rax = 3.75 m) with those in the inwardly shifted magnetic configuration (Rax = 3.6 m). It was found that the maximum energies of particles starting from the core plasma region exceed 300 keV and that such particles are confined within the vacuum vessel wall for 10-4 s. It was confirmed that the ICRF-heated particles with energies of around 400 keV are lost through the divertor field lines. The maximum energy of the ICRF-heated particles starting from the core region rises with increasing electron temperature. As a result, the energy level relevant to the proton (p)–boron (11B) fusion reaction (≃ 650 keV) was obtained when Te > 30 keV. Through acceleration in both the parallel and the perpendicular direction to the magnetic field, the high-energy chaotic orbit particles were produced by ICRF heating. It was also found that the energy at which the transition to the high-energy chaotic orbit particle occurs determines the upper energy limit of the ICRF-heated particle in LHD. A high confinement performance was found for the high-energy chaotic orbit particles produced by the ICRF field. The particle orbits in the inwardly shifted magnetic configuration were more widespread within the core region. Thus, it was concluded that the ICRF heating efficiency of the core plasma region in the inwardly shifted magnetic configuration exceeds that in the standard magnetic configuration.