Polarized proton beams from a laser-plasma accelerator

Abstract

We report on the concept of an innovative laser-driven plasma accelerator for polarized proton (or deuteron) beams with a kinetic energy up to several GeV. In order to model the motion of the particle spins in the plasmas, these have been implemented as an additional degree of freedom into the Particle-in-Cell simulation code VLPL. For the experimental realization, a polarized HCl gas-jet target is under construction, where the degree of proton polarization is determined with a Lamb-shift polarimeter. The final experiments, aiming at the first observation of a polarized particle beam from laser-generated plasmas, will be carried out at the 10 PW laser system SULF at SIOM/Shanghai.

Generation of polarized particle beams at relativistic laser intensities

“…These processes can be modeled with the help of full three-dimensional particle-in-cell (PIC) simulations, incorporating the spin dynamics via the Thomas-Bargmann Michel Telegdi (T-BMT) equation (see Equation (2) below) [47,48] . A couple of such codes have been developed recently, and used for the modeling of polarized electron [45,46,49,50] and proton [51][52][53][54] beam generation.…”

“…(3) The first applications of pre-polarized targets employed by Wen et al [45] and Wu et al [46,49,50] were actually aiming at the laser-induced acceleration of proton beams [51][52][53][54] . This is because protons have much smaller magnetic moments and, therefore, their spin alignment in the plasma magnetic fields is much more inert as compared to electrons.…”

“…Hützen et al [51][52][53] present the first scheme for a laser-based accelerator for polarized particle beams using 3D PIC simulations with explicit spin treatment. They can show that proton polarization is sufficiently conserved during the acceleration process for foil [51] and gaseous [53] targets and, thus, suggest the use of pre-polarized monatomic gases from photodissociated hydrogen halide molecules in combination with peta-watt (PW) lasers.…”

JuSPARC - The Jülich Short-Pulsed Particle and Radiation Center

“…Despite much progress in understanding fundamental physical phenomena, it is largely unexplored how the particle spins are in uenced by the huge magnetic elds inherently present in the plasma and, thus, how highly polarized particle beams can be produced in laser-driven plasmas. For the experimental realization of an innovative laser-driven plasma accelerator for polarized proton beams, a novel laser-based target system is needed: two laser beams are focused into a gas jet made of bi-atomic linear molecules with at least one Hydrogen atom like, for example, HCl gas (Büscher et al, 2019;Hützen et al, 2019). The peculiarity of the used EKSPLA SL330 series JuSPARC_MIRA system is the simultaneous output of the fundamental wavelength at 1064 nm and the fth harmonic at 213 nm provided by a Nd:YAG crystal serving as active medium.…”

“…A photo-diode, exchangeable with the gas nozzle, guarantees the control of the spatial and temporal overlap of the two beams. The ultimate goal of building the next generation of highly compact and cost-e ective electron and proton accelerator facilities using a plasma as the accelerating medium requires three challenges to be meet: (i) alignment of the electron/proton spins before accelerating laser irradiation since a signi cant buildup of the polarization, unlike at conventional accelerators, cannot happen in an initially unpolarized target (Büscher et al, 2019;Hützen et al, 2019;Thomas et al, 2019). On the other hand, an initially polarized particle ensemble can be depolarized via spin precession around the laser or plasma magnetic elds This e ect is characterized by the Thomas-Bargmann-Michel-Telegdi (T-BMT) equation.…”