The meandering orbit effect on stabilization of the tilting instability in a field-reversed configuration

The ion kinetic effect in the tilt disruption of a field-reversed configuration is investigated by means of a three-dimensional particle simulation. It is found that the tilt disruption is completely suppressed when s-bar [approximately-equal-to]1, where s-bar measures the number of ion gyroradii over the radial distance between the magnetic separatrix line and the field-null line. A prolate magnetic well is formed around the field-null line, in which ions do not execute gyration but meander along the field-null line. For the case of s-bar [approximately-equal-to]1 a large number of ions exist in the magnetic well and move on stable orbits around the major axis with an average rotation velocity nearly equal to half the thermal velocity. As s-bar becomes larger than 1, the number of ions in the magnetic well decreases and the stabilization effect is reduced. It is also found that an anisotropy is created in the ion thermal pressure profile owing to the anisotropy of the meandering orbits and that the electric field fluctuation always remains at a low level, and thus the electric field plays no essential role in the tilt stabilization