  High-flux polarized particle beams are of critical importance for the
investigation of spin-dependent processes, such as in searches of physics
beyond the Standard Model, as well as for scrutinizing the structure of solids
and surfaces in material science. Here we demonstrate that kiloampere polarized
electron beams can be produced via laser-wakefield acceleration from a gas
target. A simple theoretical model for determining the electron beam
polarization is presented and supported with self-consistent three-dimensional
particle-in-cell simulations that incorporate the spin dynamics. By
appropriately choosing the laser and gas parameters, we show that the
depolarization of electrons induced by the laser-wakefield-acceleration process
can be as low as 10%. Compared to currently available sources of polarized
electron beams, the flux is increased by four orders of magnitude.
