Polarized proton beams from laser-induced plasmas

Abstract

We report on the concept of an innovative source to produce polarized proton/deuteron beams of a kinetic energy up to several GeV from a laser-driven plasma accelerator. Spin effects have been implemented into the PIC simulation code VLPL to make theoretical predictions about the behavior of proton spins in laser-induced plasmas. Simulations of spinpolarized targets show that the polarization is conserved during the acceleration process. For the experimental realization, a polarized HCl gas-jet target is under construction using the fundamental wavelength of a Nd:YAG laser system to align the HCl bonds and simultaneously circular polarized light of the fifth harmonic to photo-dissociate, yielding nuclear polarized H atoms. Subsequently, their degree of polarization is measured 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.

Polarized electron-beam acceleration driven by vortex laser pulses

“…With this in mind, the all-optical scheme is sketched in figure 1. A spin-polarized hydrogen-atom target is prepared [16] from the photodissociation of HCl gas emitted from a nozzle. The bolds of HCl molecule are aligned by an 1064 nm infrared (IR) light (laser) first.…”

“…For electron spin of s=+1/2, there exist two combinations of spin states |s=+1/2, n=+1/2> and |s=+1/2, n=−1/2> in the atoms (n is the nuclei spin). The first hyperfine state is an eigenstate and remains unchanged but the latter oscillates between |s=+1/2, n=−1/2> and |s=−1/2, n=+1/2> at a period of 350 ps [16,26,27]. To maximize the polarization of electrons for LWFA, the time delay between the driving pulse and the photodissociation UV light should be controlled, for example, at a precision of one-tenths of the oscillation period.…”

“…The latter, due to the extremely high acceleration gradient, promises a more compact and cost-efficient approach for electron acceleration. However, for the realization of a laser-driven accelerator for polarized electron beams several challenges need to be addressed: (i) since a significant build-up of electron polarization from an initially unpolarized target during laser acceleration does not happen [16,17], it requires the use of a gas target where the electron spins are already aligned before laser irradiation. (ii) Polarization losses during the injection of as many as possible electrons into a bubble structure and (iii) subsequent acceleration in the wake field must be kept under control and minimized.…”

“…It is also predicted that the polarization can reach 90% by adapting ultraviolet (UV) light [19,20]. The most promising approach seems to be a technique employing the UV photodissociation of hydrogen halides [16,24,25], reaching gas densities of approx. 10 19 cm −3 at high polarization of the electrons in the hydrogen and halogen atoms [26][27][28] (see detail in section 2).…”

Mapping electromagnetic fields structure in plasma using a spin polarized electron beam

“…Thus the electron may radiate a photon and transform the state from parallel to antiparallel. By such way it takes several minutes or longer to build up polarization in the storage ring 33 . Therefore, in our femtosecond time scale case, Sokolov-Ternov effect can be neglected.…”