Spin-polarized proton beam generation from gas-jet targets by intense laser pulses

Polarized proton acceleration in ultraintense laser interaction with near-critical-density plasmas

The production of polarized proton beams with multi-GeV energies in ultraintense laser interaction with targets is studied with three-dimensional particle-in-cell simulations. A near-critical density plasma target with prepolarized proton and tritium ions is considered for the proton acceleration. The prepolarized protons are initially accelerated by laser radiation pressure before injection and further acceleration in a bubblelike wakefield. The temporal dynamics of proton polarization is tracked via the Thomas-Bargmann-Michel-Telegdi equation and it is found that the proton polarization state can be altered by both the laser field and the magnetic component of the wakefield. The dependence of the proton acceleration and polarization on the ratio of the ion species is determined and it is found that the protons can be efficiently accelerated as long as their relative fraction is less than 20%, in which case the bubble size is large enough for the protons to obtain sufficient energy to overcome the bubble injection threshold.

Ultrahigh-density spin-polarized hydrogen isotopes from the photodissociation of hydrogen halides: new applications for laser-ion acceleration, magnetometry, and polarized nuclear fusion

Recently, our group produced spin-polarized hydrogen (SPH) atoms at densities of at least 1019 cm-3 from the photodissociation of hydrogen halide molecules with circularly polarized UV light and measured them via magnetization-quantum beats with a pickup coil. These densities are approximately 7 orders of magnitude higher than those produced using conventional methods, opening up new fields of application, such as ultrafast magnetometry, the production of polarized MeV and GeV particle beams, such as electron beams with intensities approximately 104 higher than current sources, and the study of polarized nuclear fusion, for which the reaction cross sections of D-T and D-3He reactions are expected to increase by 50% for fully polarized nuclear spins. We review the production, detection, depolarization mechanisms, and potential applications of high-density SPH.

Energetic spin-polarized proton beams from two-stage coherent acceleration in laser-driven plasma

We propose a scheme to overcome the great challenge of polarization loss in spin-polarized ion acceleration. When a petawatt laser pulse penetrates through a compound plasma target consisting of a double layer slab and prepolarized hydrogen halide gas, a strong forward moving quasistatic longitudinal electric field is constructed by the self-generated laser-driven plasma. This field with a varying drift velocity efficiently boosts the prepolarized protons via a two-stage coherent acceleration process. Its merit is not only achieving a highly energetic beam but also eliminating the undesired polarization loss of the accelerated protons. We study the proton dynamics via Hamiltonian analyses, specifically deriving the threshold of triggering the two-stage coherent acceleration. To confirm the theoretical predictions, we perform three-dimensional PIC simulations, where unprecedented proton beams with energy approximating half GeV and polarization ratio ∼ 94% are obtained.