Enhanced polarized proton acceleration driven by femtosecond laser pulses irradiating a micro-structured solid–gas target

Abstract

Herein, we propose a scheme based on collision-less shock acceleration (CSA) involving the use of composite targets comprising a micro-structured foil and pre-polarized gas for obtaining high-energy polarized proton beams. Femtosecond laser pulses irradiate a microwire-array (MWA) target and efficiently heat the dense plasma, which moves toward the dilute plasma. Shocks are then introduced in the pre-polarized gas and accelerate upstream spin-polarized protons to relativistic velocities. Based on particle-in-cell simulations with added spin dynamics, protons with energies of 30–300 MeV are produced, and the polarization rate of protons in the high-energy region exceeds 90%. The simulations demonstrate an evident increase in the temperature and number of hot electrons owing to the presence of MWA structures, which increase both the longitudinal electric field strength associated with the shock and the energy of the reflected protons. During CSA, the bipolar magnetic field driven by hot-electron currents demonstrates a weak effect on the polarization level of the accelerated protons, resulting in a high polarization rate. The relationship between the energy of the polarized proton beam and the hot-electron temperature enables an optimization of the micro-structured target or other target components to enhance proton quality via the CSA process.

Spin-polarized 3He shock waves from a solid-gas composite target at high laser intensities

“…This scheme of CSA has been proposed for spin-polarized proton beams from an HCl target by Yan et al [21,22]. In a separate publication, they investigated shock acceleration using a microstructured foil [23]. Alternatively, CSA can also be realized without a foil, utilizing just a density-ramp [24].…”