  In galaxy clusters, the intracluster medium (ICM) is expected to host a
diffuse, long-lived, and invisible population of "fossil" cosmic-ray electrons
(CRe) with 1-100 MeV energies. These CRe, if re-accelerated by 100x in energy,
can contribute synchrotron luminosity to cluster radio halos, relics, and
phoenices. Re-acceleration may be aided by CRe scattering upon the
ion-Larmor-scale waves that spawn when ICM is compressed, dilated, or sheared.
We study CRe scattering and energy gain due to ion cyclotron (IC) waves
generated by continuously-driven compression in 1D fully kinetic
particle-in-cell simulations. We find that pitch-angle scattering of CRe by IC
waves induces energy gain via magnetic pumping. In an optimal range of
IC-resonant momenta, CRe may gain up to ~10-30% of their initial energy in one
compress/dilate cycle with magnetic field amplification ~3-6x, assuming
adiabatic decompression without further scattering and averaging over initial
pitch angle.
