Towards spin-polarized electron beams from a laser-plasma accelerator

Polarized beams are indispensable for many particle, atomic, and nuclear physics experiments where spin-dependent processes are to be studied. Currently, the primary sources of polarized electron beams, such as storage rings and polarized photo-cathodes, depend on radio-frequency (RF) technology, particularly for subsequent acceleration. As a result, they are characterized by their substantial size and limited availability. Unlike RF accelerators, the accelerating fields in Laser-Plasma-Accelerators (LPA) are not limited by material breakdown. LPAs can create beams of tens to hundreds of MeV in only a millimetre, which makes them a promising alternative to conventional accelerators. Compact polarized LPAs could help make polarized sources ubiquitous to facilitate many more polarized physics experiments. The LEAP (Laser Electron Acceleration with Polarization) project at DESY aims to generate and measure spin-polarized electron beams from a compact LPA for the first time. Spin-polarized electron beams can be generated from an LPA using a pre-polarized plasma source, where a circularly polarized UV laser pulse dissociates hydrogen halide molecules. Due to the expected beam energy of tens of MeVs, photon transmission polarimetry will be used for the subsequent polarization measurement in LEAP.