  Electron beam polarization in the bubble regime of the interaction between a
high-intensity laser and a longitudinally pre-polarized plasma is investigated
by means of the Thomas-Bargmann-Michel-Telegdi equation. Using a test-particle
model, the dependence of the accelerated electron polarization on the bubble
geometry is analyzed in detail. Tracking the polarization dynamics of
individual electrons reveals that although the spin direction changes during
both the self-injection process and acceleration phase, the former has the
biggest impact. For nearly spherical bubbles, the polarization of electron beam
persists after capture and acceleration in the bubble. By contrast, for
aspherical bubble shapes, the electron beam becomes rapidly depolarized, and
the net polarization direction can even reverse in the case of a oblate
spheroidal bubble. These findings are confirmed via particle-in-cell
simulations.
