Onset and saturation of ion heating by odd-parity rotating magnetic fields in a field-reversed configuration

Heating of figure-8 orbit ions by odd-parity rotating magnetic fields (RMFo) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s equivalent to omega(R)/omega) of the RMFo frequency, omega(R), with the figure-8 orbital frequency, omega, and is proportional to s(2) for s-even resonances and to s for s-odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude.