Highly Nuclear-Spin-Polarized Deuterium Atoms from the UV Photodissociation of Deuterium Iodide

Abstract

We report the production of highly spin-polarized Deuterium atoms via photodissociation of deuterium iodide at 270 nm. The velocity distribution of both the deuterium and iodine photodissociation products is performed via velocity mapping slice-imaging. Additionally, the angular momentum polarization of the iodine products is studied using polarization-sensitive ionization schemes. The results are consistent with excitation of the A 1 Π1 state followed by adiabatic dissociation. The process produces ∼100% electronically polarized deuterium atoms at the time of dissociation, which is then converted to ∼ 60% nuclear D polarization after ∼ 1.6 ns. These production times for hyperpolarized deuterium allow collision-limited densities of ∼ 10 18 cm −3 , which is ∼ 10 6 times higher than conventional (Stern-Gerlach separation) methods. We discuss how such high-density hyperpolarized deuterium atoms can be combined with laser fusion to measure polarized D-D fusion cross sections.PACS numbers: 33.80. Gj, 32.10.Fn Controlling the nuclear spin polarization in fusion reactions offers important advantages, such as larger reaction cross sections, control over the emission direction of products, and in some cases eliminating hazardous neutron emission [1,2]. In the case of the five-nucleon reactions D + T → n + 4 He and D + 3 He → p + 4 He, it is well known that the reaction cross section increases by ∼50% when the fused nuclei have oriented nuclear spins [3,4].For the 4-nucleon D+D reaction, over the important energy range of 10-100 keV, the situation is unclear, since several predictions range from enhancement of the reaction, suppression of the reaction, or almost no effect at all [5][6][7][8][9][10]. The technical challenges of measuring fusion polarization dynamics limits the number of experiments which pursue this direction to two facility-scale experiments [11]. These experiments achieve nuclear spin polarization by magnetically separating the nuclear spin states via the Stern-Gerlach effect in molecular beams, a process however which limits the achievable production rates to ∼ 10 16 atoms s −1 [2], and the projected D-D fusion reaction rate to as low as ∼0.01 neutrons s −1 [12]. Polarized solid deuterium targets can be produced where the densities can reach as high as 2.5 × 10 19 spins/cm 3 , albeit in much lower polarization close to 10% [13]. Another approach for the production of polarized sold fuel involves accumulating the hyperpolarized deuterium in specially coated storage cells [11].Laser photodissociation of hydrogen halides has been shown to produce highly polarized H atoms [14][15][16][17]. The photodissociation process initially polarizes the electron spin up to 100% (for photofragment velocities parallel to the propagation direction of the circularly-polarized dissociation laser) [18]; due to the hyperfine interaction, the polarization oscillates back and forth between the electronic and the nuclear spin on the ∼1-ns timescale. By terminating this polarization exchange appropriately, for example by ioni...

Polarized electron-beam acceleration driven by vortex laser pulses

“…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).…”

Polarized Laser-WakeField-Accelerated Kiloampere Electron Beams

“…In particular, hydrogen halides were used to generate dense electronically polarized hydrogen and deuterium atoms [20,25]. In this case, the presence of other species than hydrogen implies that, although the IEP of hydrogen can reach 100% [20], the global IEP of the generated plasma is less than unity. However, as it will be clear in the following, only optical laser pulses with intensity of the order of 10 18 W/cm 2 drive laser-wakefield acceleration without significant electron beam depolarization.…”

An ultrahigh vacuum apparatus for H atom scattering from surfaces

“…In principle, a spin polarized version of the presented experiments could be possible using special dissociation and detection schemas. [32][33][34][35] Currently, we are working on the realization of a short pulse version to perform pump-probe experiments with a H atom beam in combination with an ultra-short laser pulse. 36 Furthermore, we want to expand the source concept for atomic…”