Particle confinement in axisymmetric poloidal magnetic field configurations with zeros of B:: Methodological note

Collisionless particle confinement in axisymmetric configurations with magnetic field nulls is analyzed. The existence of an invariant of motion-the generalized azimuthal momentum-makes it possible to determine in which of the spatial regions separated by magnetic separatrices passing through the magnetic null lines the particle occurs after it leaves the vicinity of a magnetic null line. In particular, it is possible to formulate a sufficient condition for the particle not to escape through the separatrix from the confinement region to the external region. In the configuration under analysis, the particles can be lost from a separatrix layer with a thickness on thj'order of the Larmor radius because of the nonconservation of the magnetic moment mu. In this case, the variations in mu are easier to describe in a coordinate system associated with the magnetic surfaces. An analysis is made of the applicability of expressions for the single-pass change Delta mu in the magnetic moment that were obtained in different magnetic field models for a confinement system with a divertor (such that there is a circular null line). (c) 2005 Pleiades Publishing, Inc.