On the robustness of spin polarization for magnetic vortex accelerated proton bunches in density down-ramps

We investigate the effect of density down-ramps on acceleration ions via Magnetic Vortex Acceleration (MVA) in a near-critical gas target by means particle-in-cell simulations. The spin-polarization accelerated protons is robust for variety ramp lengths at around 80%. Significant increase length accompanied collimation low-polarization into final beam and large transverse spread highly polarized with respect to direction laser propagation.