The spin dynamics of water ice in the presence of external magnetic fields are investigated. The employed model is based on the approach introduced by Buntkowsky et al. (2008), which considers two nearest-neighbor water molecules and yields a four-spin system, as the abundant oxygen isotope has zero nuclear spin. The model is extended to include coupling to external magnetic fields, allowing us to analyze the interplay between magnetic dipole–dipole interactions and magnetic field coupling. Two types of configurations are examined: (i) static, homogeneous fields, corresponding to a time-independent interaction, and (ii) spatially varying sinusoidal fields in relative motion with the molecules, leading to a time-dependent interaction. All computations are performed within the density operator formalism. The ortho/para populations and the total spin projections are evaluated during the first tens of milliseconds following the gas-to-solid phase transition. For static homogeneous fields, we show that increasing field strength suppresses dipolar-induced depolarization. Assuming that all molecules are initially in the para state, we show that static homogeneous fields can drive the ortho population up to approximately 50%, whereas suitably chosen sinusoidal-field configurations can increase it beyond 90%. These results are relevant for schemes aiming to preserve or manipulate nuclear-spin polarization during deposition.

Pinching of the driver beam in plasma wakefield acceleration is generally considered an unwanted effect that needs to be mitigated. Here, we propose that this effect can be utilized for the injection of spin-polarized electron beams from hydrogen halide targets into wakefields. Particle-in-cell simulations show that the electron spin is preserved on a level of 50

Spin-polarized electron beams are essential tools for probing fundamental symmetries and for the search beyond the Standard Model. While plasma-based accelerators are a promising pathway towards higher-energy frontiers, they have so far failed to deliver a competitive polarized source: existing proposals are challenging to realize and achievable polarizations remain far below conventional sources. Here, we introduce a photocathode-like scheme, applied to a gas of pre-polarized hydrogen and halogen atoms. A VUV and a visible laser pulse excite the halogen atoms to create a two-component ionization medium, consisting of low-threshold excited halogen atoms and high-threshold polarized hydrogen. Particle-in-cell simulations show witness beams with tens of pC charge retaining up to 97

The preservation of nuclear spin alignment in plasmas is a prerequisite for important applications, such as energy production through polarized fusion or the acceleration of polarized particle beams. Although this conservation property has been the basis of numerous theoretical papers, it has never been experimentally confirmed. Here, we report on first experimental data from a polarized 3He target heated by a PW laser pulse, showing evidence consistent with the persistence of nuclear polarization after acceleration to MeV energies via Coulomb explosion of a plasma channel. Our results confirm the theoretically established concept of using pre-polarized targets for experiments in high-power laser facilities.

The preservation of witness beam polarization in wakefield accelerators will be crucial for future collider applications. While extensive theoretical studies on the injection and initial acceleration of polarized electrons exist, a study concerning higher-energy regimes has been neglected thus far. Besides the spin precession usually considered in wakefield-related research, radiative effects could become increasingly relevant at higher energies as the witness electrons perform betatron oscillations during which they will emit photons. In the present study, we use particle-in-cell simulations extended with Monte-Carlo routines to study the influence of radiative spin-flips on beam polarization. We find that at high energies, the importance of radiative effects on beam polarization mainly comes down to the alignment of the witness beam with respect to the wakefield.

Polarized particle sources have a plethora of applications, ranging from deep-inelastic scattering to nuclear fusion. One crucial challenge in laser–plasma interaction is maintaining the initial polarization of the target. Here, we propose the acceleration of spin-polarized helium-3 from near-critical density targets using high-intensity Laguerre–Gaussian laser pulses. Three-dimensional particle-in-cell simulations show that magnetic vortex acceleration with these modes yields high polarization at the $90\%$ level, while also providing low-divergence beams.

We study the interaction of high-intensity Laguerre Gaussian laser pulses with hydrogen-boron compounds targets using 3D particle-in-cell simulations. The ratio of hydrogen to boron is varied throughout different simulation runs as a proxy model for various borane molecules that can be synthesized. We show that the strength of the axial magnetic fields generated via the Inverse Faraday effect depends on the specific ratio of target components, making boranes and the option to tune their composition of interest for proton-boron fusion.

The PREFER (Polarization REsearch for Fusion Experiments and Reactors) collaboration was born to address the know–how in different fields and techniques to the challenging bet on fusion energy production with polarized fuel. Efforts are focused on a variety of tasks and objectives, which are under the responsibility of different institutes. Starting from open questions in the fusion reaction physics, such as the study of D+D spin–dependent cross–sections to measurements of nuclear polarization conservation in laser–induced fusion plasmas, there is still unexplored territory to discover. The collaboration aims to produce nuclear–spin polarized molecules, recombined from polarized atomic beams, and their condensation and transport, or explore a resonance ("Sona") transition technique, which promises sufficient intensity for the feeding of fusion reactors. Other options of production are investigated, like nuclear–spin polarization of molecules by laser or microwave excitation. The presentation provides the status of proposals and investigations in the European community.

Polarized electron beam production via laser wakefield acceleration in pre-polarized plasma is investigated by particle-in-cell simulations. The evolution of the electron beam polarization is studied based on the Thomas-Bargmann-Michel-Telegdi equation for the transverse and longitudinal self-injection, and the depolarization process is found to be influenced by the injection schemes. In the case of transverse self-injection as found typically in the bubble regime, the spin precession of the accelerated electrons is mainly influenced by the wakefield. However, in the case of longitudinal injection in the quasi-one-dimensional regime (for example, F. Y. Li \emph{et al}., Phys. Rev. Lett. 110, 135002 (2013)), the direction of electron spin oscillates in the laser filed. Since the electrons move around the laser axis, the net influence of the laser field is nearly zero and the contribution of the wakefield can be ignored. Finally, an ultra-short electron beam with polarization of $99\%$ can be obtained using longitudinal self-injection.

Polarized $^3$He ions have promising applications in nuclear physics as an ideal substitute for polarized neutron beams, and in fusion research as fuel for polarized nuclear fusion. However, current methods are limited in achievable intensity or polarization and require complex sources. Our new approach promises to overcome these limitations with an intense polarized $^3$He beam with a polarization up to 𝑃 ∼ 0.9. The method is theoretically well understood and uses single radio wave pulses to induce transitions within the hyperfine structure in the Zeeman region of $^3$He$^+$. In this way, the three substates of the 𝐹 = 1 triplet can be pumped into a single one, leading to a nuclear polarization. Experimentally, the achievable polarization is planned to be measured after acceleration of the $^3$He ions with the cyclotron JULIC using the known analyzing powers of the elastic scattering on protons in the 10–100 MeV energy range.

AbstractThe mechanism of THz generation in ferromagnet/metal (F/M) bilayers has been typically ascribed to the inverse spin Hall effect (ISHE). Here, we fabricated Pt/Fe/Cr/Fe/Pt multilayers containing two back-to-back spintronic THz emitters separated by a thin (tCr≤ 3nm) wedge-shaped Cr spacer. In such an arrangement, magnetization alignment of the two Fe films can be controlled by the interplay between Cr-mediated interlayer exchange coupling (IEC) and an external magnetic field. This in turn results in a strong variation of the THz amplitude A, with A↑↓ reaching up to 14 times A↑↑ (arrows indicate the relative alignment of the magnetization of the two magnetic layers). This observed functionality is ascribed to the interference of THz transients generated by two closely spaced THz emitters. Moreover, the magnetic field dependence A(H) shows a strong asymmetry that points to an additional performance modulation of the THz emitter via IEC and multilayer design.

We present a laser–plasma electron accelerator module designed to be driven by high-repetition-rate lasers for industrial applications of laser-driven electron beams. It consists of a single vacuum chamber containing all the necessary components for producing, optimizing, and monitoring electron beams generated via laser wakefield acceleration in a gas jet when driven by a suitable laser. The core methods in this paper involve a comprehensive metrological assessment of the driving laser by rigorous temporal laser pulse characterization and contrast measurements, supplemented by detailed spatiotemporal distribution analyses of the laser focus. Results demonstrate the good stability and reproducibility of the laser system, confirming its suitability for advanced scientific and industrial applications. We further demonstrate the functionality of the laser–plasma accelerator module diagnostics, perform target density characterizations, and time-resolved laser–plasma shadowgraphy. Current limitations of the set-up preventing first electron acceleration are analyzed and an outlook for future experiments is given. Our work is a first step towards the wide dissemination of fully integrated laser–plasma accelerator technology.

Intensity of THz transients triggered by laser excitation in NM/FM/NM/FM/NM multilayers (FM - ferromagnet, NM - normal metal) can be tuned by the interlayer exchange coupling between the two FM layers. We ascribe this tunability to the constructive and destructive interference of the THz transients generated by closely-spaced NM/FM and FM/NM spintronic THz emitters.

Sizable hyperpolarisation, i.e. an imbalance of the occupation numbers of nuclear spins in a sample deviating from thermal equilibrium, is needed in various fields of science. For example, hyperpolarised tracers are utilised in magnetic resonance imaging in medicine (MRI) and polarised beams and targets are employed in nuclear physics to study the spin dependence of nuclear forces. Here we show that the quantum interference of transitions induced by radio-wave pumping with longitudinal and radial pulses are able to produce large polarisations at small magnetic fields. This method is easier than established methods, theoretically understood and experimentally proven for beams of metastable hydrogen atoms in the keV energy range. It should also work for a variety of samples at rest. Thus, this technique opens the door for a new generation of polarised tracers, possibly low-field MRI with better spatial resolution or the production of polarised fuel to increase the efficiency of fusion reactors by manipulating the involved cross sections.

Molecular photodissociation is an innovative method for the preparation of polarized atoms and molecules. It is a fundamental chemical process that involves the absorption of one or more polarized photons by a molecule including its fragmentation into polarized atomic (or molecular) fragments. Recently, T. P. Rakitzis' group produced high densities of spin-polarized hydrogen atoms applying molecular photodissociation to hydrogen halides. The obtained densities (10(19) cm(-3)) and short production times (ns timescales) surpass by several orders of magnitude conventional methods such as spin-exchange optical pumping and Stern-Gerlach spin separation. These density and time regimes make it an ideal candidate for a broad range of applications, e.g., laserinduced acceleration from polarized gas targets and polarized five-nucleon fusion reactions (d-3H, d-He-3). The second has been shown to have an increased cross section by similar to 50% compared to the unpolarized case. The photodissociation method has been adopted by M. Buscher's group for the production of polarized proton and deuteron beams at the Forschungszentrum Julich. Here, we report on the production and detection scheme of these beams.

During the last 60 years, Sona transition devices have been used to invert the occupation numbers of pure states by a rapidly changing magnetic field across a zero crossing point. The inversion of the magnetic quantisation axis changes so fast that the Lamor precession cannot follow. In addition, spectroscopic measurements of the hyperfine splitting are possible. In the present setup hydrogen atoms move at a constant velocity through the Sona unit. Therefore, the Sona unit provides the region where the beam passes a static magnetic field with a gradient. It has the shape of a sine-function in z- and a cosine-function in radial direction. Thus the hydrogen atom experiences a time-varying electromagnetic field, which leads to transitions between the hyperfine states in the Breit-Rabi diagram. The beam velocity is directly proportional to the "photon" energy necessary to achieve a transition. Finally, the big advantage is that low beam energies (0.5 keV) are already enough to induce the transitions at E approximate to 5 neV and its odd multiples, which gives the possibility to have a precession high enough to even observe the QED-corrections.