Analysis of the alpha particle orbits in the high beta plasma of the Large Helical Device

We investigate the orbits of the 3.5 MeV alpha particles in the high beta plasma of the Large Helical Device (LHD), in which B=6 T is assumed. For this purpose, we trace the 100 keV proton in the case of B=1 T, the Larmor radius of which is almost the same as the Larmor radius of the alpha particle, by numerical solving the guiding-center equations. As a result, the particle orbit characteristics in the high beta plasma of the LHD are shown in detail. We point out the importance to appropriately trace the re-entering particles in the analyses of the orbits of the high-energy particles, such as the alpha particles, in the high beta plasma. It is found that the lifetime of the alpha particles depends on the lifetime of the chaotic orbit particles almost all of which is lost. The chaotic orbit particles are lost before they heat fuels because the lifetime of the chaotic orbit particles is much shorter than the alpha-electron relaxation, time. (author)