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

Heating of figure-8 ions by odd-parity rotating magnetic fields ($RMF_o$) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances ($s \equiv \omega_R/ \omega$) of the $RMF_o$ 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.