Enhanced MVA of polarized proton beams via PW laser-driven plasma bubble

The significance of laser-driven polarized beam acceleration has been increasingly recognized in recent years. We propose an efficient method for generating polarized proton beams from a pre-polarized hydrogen halide gas jet, utilizing magnetic vortex acceleration enhanced by a laser-driven plasma bubble. When a petawatt laser pulse passes through a pre-polarized gas jet, a bubble-like ultra-nonlinear plasma wave is formed. As a portion of the particles constituting this wave, background protons are swept by the acceleration field of the bubble and oscillate significantly along the laser propagation axis. Some of the pre-accelerated protons in the plasma wave are trapped by the acceleration field at the rear side of the target. This acceleration field is intensified by the transverse expansion of the laser-driven magnetic vortex, resulting in energetic polarized proton beams. The spin of energetic protons is determined by their precession within the electromagnetic field, which is described using the Thomas–Bargmann–Michel–Telegdi equation in analytical models and particle-in-cell simulations. Multidimensional simulations reveal that monoenergetic proton beams with an energy of hundreds of MeV, a beam charge of hundreds of pC, and a beam polarization of tens of percent can be produced at laser powers of several petawatts. Such laser-driven polarized proton beams have promise for application in polarized beam colliders, where they can be utilized to investigate particle interactions and to explore the properties of matter under extreme conditions.