  The stability of charged particle motion in a uniform magnetic field with an
added spatially uniform transverse rotating magnetic field (RMF) is studied
analytically. It is found that the stability diagram of a single-particle's
orbit depends critically on the chosen boundary conditions. We show that for
many boundary conditions and wide regions in the parameter space, RMFs
oscillating far below the cyclotron frequency can cause linear instabilities in
the motion which break $\mu$-invariance and energize particles. Such
energization may appear at odds with the adiabatic invariance of $\mu$;
however, adiabatic invariance is an asymptotic result, and does not preclude
such heating by magnetic fields oscillating at slow frequencies. This mechanism
may contribute to heating in the edge plasma of field-reversed configurations
(FRCs) in rotamak-FRC experiments. Furthermore, these RMF-driven instabilities
may significantly enhance azimuthal current drive during the formation of FRCs
in such devices.
