Laser-induced acceleration of Helium ions from unpolarized gas jets

Abstract

In order to develop a laser-driven spin-polarized 3He-ion beam source available for nuclear-physics experiments as well as for the investigation of polarized nuclear fusion, several challenges have to be overcome. Apart from the provision of a properly polarized 3He gas-jet target, one of the biggest milestones is the demonstration of the general feasibility of laser-induced ion acceleration out of gas-jet targets. Of particular importance is the knowledge about the main ion-emission angles as well as the achievable ion-energy spectra (dependent on the optimal set of laser and target parameters). We report on the results of such a feasibility study performed at PHELIX, GSI Darmstadt. Both 3He- and 4He-gas jets (n gas ∼ 1019 cm−3) were illuminated with high-intensity laser pulses, I L ∼  ( 10 19 W cm − 2 ) . The main ion-emission angles could be identified (±90° with respect to the laser-propagation direction) and the ion-energy spectra for all ion species could be extracted: for the optimal laser and target parameters, the high-energy cut-offs for He 2 + , 1 + ions were 4.65 MeV (with a normalized energy uncertainty of Δ   − 1 = 0.033 ) and 3.27 MeV ( Δ   − 1 = 0.055 ), respectively.

Production of HD Molecules in Definite Hyperfine Substates

“…In the next step the polarized D 2 and HD molecules will be frozen as polarized ice on a cold surface inside a strong magnetic field exploiting the higher evaporation temperature of the H 2 molecules. The goal is to build polarized targets for laser-acceleration experiments to produce polarized proton and deuteron beams [16]. Polarized H + 2 and HD + ions in single spin-isomers are a perfect tool for precision spectroscopy of this most simple molecular ions, because the influence of the spindependent part of the transition-frequencies can be determined separately [17].…”

Generation of polarized particle beams at relativistic laser intensities

“…(4) The first attempt to experimentally study spin effects during laser-induced acceleration is based on a nuclear polarized 3 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).…”

“…Early attempts to Figure 7. Measured 3,4 He 2+ energy spectra accelerated from unpolarized helium gas jets [56] . IP, image plate.…”

“…No PIC simulations with treatment of spin effects have so far been carried out for particles heavier than protons. Only a scan of the parameter space (target density, laser pulse energy and duration) has been published [56] , aiming at the optimization of the ion flux and kinetic energy accelerated in a polarized gas-jet target; see Figure 16. It is seen that a channel in the ion density is generated via a combination of strong self-focusing and radial ponderomotive expulsion of electrons within the first 0.5 mm of the gas target, followed by filamentation and hosing for longer times.…”

“…Simulated normalized He 2+ ion-number density during the passage of a peta-watt laser pulse (6.5 ps after it entered the simulation box at the left boundary) through an unpolarized helium gas jet target. (a) 2%; (b) 3%; (c) 4%; (d) 12% critical density [56] . Figure 17.…”