Transit time scattering of energetic electrons due to equatorially confined magnetosonic waves

Recent analysis using quasilinear theory (QLT) has shown that magnetosonic (MS) waves are able to accelerate electrons to relativistic energies on fast time scales (similar to 1 day). However, the large obliquity of the wave and typical equatorial confinement of the MS wave power create conditions that bring into question the fundamental applicability of QLT to this problem. In this paper, a test particle code is used to model the interaction of energetic electrons with fast MS waves, to test the results of QLT analysis, and to investigate any potential nonlinear effects. It is found that in the expected Landau-resonant region, test particle results show good agreement with QLT, but outside this region, the spatial confinement of the low-frequency waves introduces a new source of scattering which we call "transit time diffusion." Although this mechanism is weaker than resonant scattering, it is nevertheless able to interfere with the Landau resonance to create nulls in the energy-pitch angle diffusion map, and the scattering persists even when resonant diffusion is completely removed.