Numerical Study of Particle Orbit in the Large Helical Device.

Abstract

The drift orbit of high energy ions under the magnetic configuration of the Large Helical Device (LHD) is pursued numerically with high accuracy and for many hours. The particle confinement characteristics of LHD is studied systematically.Particle orbits are divided roughly into five groups by the value of an initial position and pitch angle of the particles. Three groups in these form closed drift surface in their Poincare map of the orbit, and are confined perfectly in the magnetic field in case of no collisions. Another groups, which can not form closed drift surface, are composed of chaos orbit group and direct loss orbit group.Chaos orbit group is confined relatively long intervals in the magnetic field. Direct loss orbit group is lost immediately from magnetic field because magnetic field plays no role for particle confinement. Positions of lost particle are compared with divertor chart of lines of force.The phase space of particles is roughly divided into three regions: drift surface formation regions, chaos zones and direct loss regions, according to the type of orbit.Particles in the chaos regions and reflecting particles in the closed drift surface formation regions are flitting about between deep magnetic surface regions and chaotic lines of force regions outside of most outside of magnetic surface.