Magnetic field perturbations in closed-field-line systems with zero toroidal magnetic field

In some plasma confinement systems [e.g., field-reversed configurations (FRC) and levitated dipoles] the confinement is provided by a closed-field-line poloidal magnetic field. The influence of the magnetic field perturbations on the structure of the magnetic field in such systems is considered and it is found that the effect of perturbations is quite different from that in the systems with a substantial toroidal field. In particular, even infinitesimal perturbations can, in principle, lead to large radial excursions of the field lines in FRCs and levitated dipoles. Under such circumstances, particle drifts and particle collisions may give rise to significant neoclassical transport. Introduction of a weak regular toroidal magnetic field reduces radial excursions of the field lines and neoclassical transport. (C) 2004 American Institute of Physics.