Towards a Laser-driven polarized $^3$He Ion Beam Source

Abstract

In order to investigate the polarization degree of laser-accelerated 3 He ions from a pre-polarized 3 He gas-jet target, several challenges have to be overcome beforehand. One of these includes the demonstration of the feasibility of laser-induced ion acceleration out of gas-jet targets. In particular, the ion-emission angles as well as the ion-energy spectra have to be determined for future polarization measurements. Such an experiment was performed at the PHELIX Petawatt Laser Facility, GSI Darmstadt. As laser target, both 4 He, and in a second step, unpolarized 3 He gas were applied.

Generation of polarized particle beams at relativistic laser intensities

“…The first attempt to experimentally study spin effects during laser-induced acceleration is based on a nuclear polarized He target [55,56] . These experiments profit from the fact that hyperpolarized 3 He gas can be produced rather easily and maintains its nuclear polarization over several days at ambient room temperature and under small magnetic holding fields (Section 7).…”

“…The brown curve indicates the initial density distribution of the gas-jet target. The polarized proton beam is shown on the right (blue) with arrows (red) presenting the polarization direction [54] . The first attempt to experimentally study spin effects during laser-induced acceleration is based on a nuclear polarized He target [55,56] . These experiments profit from the fact that hyperpolarized 3 He gas can be produced rather easily and maintains its nuclear polarization over several days at ambient room temperature and under small magnetic holding fields (Section 7).…”

Polarized proton beams from laser-induced plasmas

“…However, solid foil targets suitable for laser acceleration with TNSA mechanism are not available so far and an experimental realization is extremely challenging. In previous experiments hydrogen nuclear polarization mostly results from a static polarization, e.g., in frozen spin targets [16] or with polarized gas [17, 18] . For the acceleration of protons until now only polarized atomic beam sources based on the Stern–Gerlach principle [19] are available, which however have the disadvantage of a too small particle density.…”

Laser-induced acceleration of Helium ions from unpolarized gas jets

“…Here, the ion-acceleration mechanisms have been described regarding the specific regimes. The first experiments at the VULCAN laser facility (50 and 180 J on target, pulse durations between 0.5 and 0.9 ps,wavelength of 1.064 μm, focus intensities of ∼1×10 20 W cm −2 , maximal plasma densities of 5×10 19 to 1×10 20 cm −3 ) yielded helium-ion energies from ∼4 MeV up to ∼13 MeV in the transverse direction (ion-emission angles between 90°and 100°). The ion-energy spectra have locally been obtained with the help of ion spectrometers which had been positioned at specific angles with respect to the laser-propagation direction.…”

“…The main ion-acceleration mechanism for this set of laser and target parameters was explained to be TNSA-like (target normal sheath acceleration). More recently in 2019, Puyuelo-Valdes et alconducted experiments at the PICO2000 facility at LULI (pulse duration of 1 ps, wavelength of 1.053 μm, focus intensity of 4×10 19 W cm −2 , maximal near-critical plasma density of 1.6×10 21 cm −3 , i.e. 1000 bar gas pressure).…”