Collisionless pitch angle scattering at field-null X-points in a Field-Reversed Configuration

The particle orbit is traced numerically in peripheral plasma of Field-Reversed Configuration to study the particle loss from the confinement system as well as physical properties of collisionless pitch angle scattering at X-points. Plasma ions are trapped near X-points for long duration and form the electrostatic potential, which affects the axial confinement. It appears the particle loss rate increases as the guiding center of edge plasma particles approaches to the separatrix. Qualitative discussion on electrostatic potential is also presented. (author)