Vincent Bagnoud

We present first experimental data obtained at the recently commissioned experimental platform to compare laser plasma instabilities (LPIs) driven by monochromatic and broad spectral bandwidth ( ≈ 0.5 % ) laser pulses with a wavelength of around 527 nm. The evaluation of LPIs at 10 ¹⁵ W cm ⁻² is shown by utilizing a full aperture backscatter diagnostic and side scatter diagnostics. For a broad bandwidth, our study indicates a suppression of stimulated Brillouin back- and side scattering as well as of the two plasmon decay instability, but an increase of stimulated Raman side scattering. An increase in both temperature and numbers of hot electrons is also identified by direct and indirect measurements.

We present an experimental and simulation-based study on ion beam deflection in laser-matter interactions conducted at the PHELIX facility. The experiment was performed using a main pulse (1053 nm, 500 fs) reaching peak intensities of ∼1.5×1021 W cm−2, and a pre-pulse (1053 nm, either 1 or 3 ns) with an intensity ranging from 6.4×1013 to 1.2×1015 W cm−2. The laser was incident on a 5 μm thick carbon foil under an angle of 25° relative to the target normal. Systematic variation of the pre-pulse delay (0–3 ns) revealed significant target deformation effects, leading to ion beam deflection and a reduction of the ion cutoff energies with increasing delay between the pre-pulse and the main pulse. The pre-plasma dynamics were characterized using side-view interferometry in combination with a synchronized picosecond probe beam. Hydrodynamic simulations with FLASH-2D were adapted to match the interferometric measurements by adjusting laser energy and focus size. The simulations confirm that the observed beam deflection originates from pre-pulse-induced target deformation and expansion. Our results demonstrate that ion beam directionality can be controlled via pre-pulse parameters, providing a pathway for optimizing laser-driven ion acceleration schemes. These findings highlight the importance of precisely adapted pre-plasma conditions in high-intensity laser-plasma interactions and their impact on acceleration dynamics.

This work presents the results of a nuclear fission experiment with depleted uranium, driven by ultra-intense multi-MeV bremsstrahlung, generated by laser-accelerated electrons in a high-Z converter, which enables the production of radioisotopes on the picosecond timescale. The advanced plasma target made of pre-ionized low-density foam enabled effective electron acceleration to energies of up to 100 MeV at a laser intensity of 1019 W cm−2 and the generation of ultra-bright bremsstrahlung with an effective temperature of 11.8 MeV in the giant dipole resonance region, with a previously unattained high conversion efficiency of 1%–2%. A major hazard in high-power laser experiments is the presence of harmful radiation and its impact on sensitive detectors. A gas flow system was used to transport volatile fission products from the laser-target interaction point to remote detectors in under ten seconds. This spatial separation of the detectors from the point of laser-matter interaction significantly reduces background noise, the impact of harmful radiation, and enables the detection of signals from short-lived radioisotopes—the products of induced nuclear fission—with high sensitivity.

We report on commissioning experiments at the high-energy, high-temperature (HHT) target area at the GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany, combining for the first time intense pulses of heavy ions from the SIS18 synchrotron with high-energy laser pulses from the PHELIX laser facility. We demonstrate the use of X-ray diagnostic techniques based on intense laser-driven X-ray sources, which will allow probing of large samples volumetrically heated by the intense heavy-ion beams. A new target chamber as well as optical diagnostics for ion-beam characterization and fast pyrometric temperature measurements complement the experimental capabilities. This platform is designed for experiments at the future Facility for Antiproton and Ion Research in Europe GmbH (FAIR), where unprecedented ion-beam intensities will enable the generation of millimeter-sized samples under high-energy-density conditions.

A new high energy proton radiography facility PRIOR-II (Proton Microscope for FAIR) has been designed, constructed, and successfully commissioned at the GSI Helmholtzzentrum für Schwerionenforschung (Darmstadt, Germany) pushing the technical boundaries of charged particle radiography with normal conducting magnets to the limits. The setup is foreseen to become a new and powerful user facility for carrying out fundamental science experiments in the fields of plasma and shock wave physics, material science, and medical physics. It will help address several unsolved scientific challenges, which require high-speed and precise non-invasive diagnostic methods capable of probing matter with up to 100 g/cm2 areal density. PRIOR-II is specifically designed to utilize the full timing capabilities of the SIS-18 synchrotron at GSI for ultra-fast dynamic experiments with up to 4 GeV protons and will also be fielded at the future FAIR facility, where higher proton energies and beam intensities will be available. This will enable experiment geometries with even higher areal densities, more flexible experiment timing, and further enhanced spatial resolution.

We present numerical simulations used to interpret laser-driven plasma experiments at the GSI Helmholtz Centre for Heavy Ion Research. The mechanisms by which non-thermal particles are accelerated in astrophysical environments, e.g., the solar wind, supernova remnants, and gamma ray bursts, is a topic of intense study. When shocks are present, the primary acceleration mechanism is believed to be first-order Fermi, which accelerates particles as they cross a shock. Second-order Fermi acceleration can also contribute, utilizing magnetic mirrors for particle energization. Despite this mechanism being less efficient, the ubiquity of magnetized turbulence in the universe necessitates its consideration. Another acceleration mechanism is the lower-hybrid drift instability, arising from gradients of both density and magnetic field, which produce lower-hybrid waves with an electric field that energizes particles as they cross these waves. With the combination of high-powered laser systems and particle accelerators, it is possible to study the mechanisms behind cosmic-ray acceleration in the laboratory. In this work, we combine experimental results and high-fidelity three-dimensional simulations to estimate the efficiency of ion acceleration in a weakly magnetized interaction region. We validate the FLASH magneto-hydrodynamic code with experimental results and use OSIRIS particle-in-cell code to verify the initial formation of the interaction region, showing good agreement between codes and experimental results. We find that the plasma conditions in the experiment are conducive to the lower-hybrid drift instability, yielding an increase in energy ΔE of ∼ 264 keV for 242 MeV calcium ions.

We present in situ measurements of spectrally resolved X-ray scattering and X-ray diffraction from monocrystalline diamond samples heated with an intense pulse of heavy ions. In this way, we determine the samples’ heating dynamics and their microscopic and macroscopic structural integrity over a timespan of several microseconds. Connecting the ratio of elastic to inelastic scattering with state-of-the-art density functional theory molecular dynamics simulations allows the inference of average temperatures around 1300 K, in agreement with predictions from stopping power calculations. The simultaneous diffraction measurements show no hints of any volumetric graphitization of the material, but do indicate the onset of fracture in the diamond sample. Our experiments pave the way for future studies at the Facility for Antiproton and Ion Research, where a substantially increased intensity of the heavy ion beam will be available.

The high-energy/high-intensity laser facility PHELIX of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany, has been in operation since 2008. Here, we review the current system performance, which is the result of continuous development and further improvement. Through its versatile frontend architecture, PHELIX can be operated in both long- and short-pulse modes, corresponding to ns-pulses with up to 1 kJ pulse energy and sub-ps, 200 J pulses, respectively. In the short-pulse mode, the excellent temporal contrast and the control over the wavefront make PHELIX an ideal driver for secondary sources of high-energy ions, neutrons, electrons and X-rays. The long-pulse mode is mainly used for plasma heating, which can then be probed by the heavy-ion beam of the linear accelerator of GSI. In addition, PHELIX can now be used to generate X-rays for studying exotic states of matter created by heavy-ion heating using the ion beam of the heavy-ion synchrotron of GSI.

The U.S. Department of Energy's Office of Scientific and Technical Information