Search

Physical review / E 107(2), 025206 (2023). doi:10.1103/PhysRevE.107.025206, Published by APS, Woodbury, NY

Magnetized plasma studies are necessary for many applied studies, including laser-driven inertial fusion, modeling astrophysically relevant phenomena, and innovative industrial and medical applications. An interesting method of generating highly magnetized plasma can be based on the interaction of a laser with spiral-shaped cavity (snail-like) targets. A target shaped in this way can represent the central area of a spherical pellet that is not irradiated radially, but rather through an entrance hole allowing the laser beam to almost impact its inner surface tangentially (Pisarczyk et al 2018 Sci. Rep. 8 17 895). In the reported experiment, snail targets of various diameters were irradiated by linearly or circularly polarized radiation of a Prague asterix laser system (PALS) iodine laser delivering ∼500 J, 350 ps and 1.315 μm pulses on targets. Three-frame complex interferometry demonstrated that plasma is generated on the entire inside and outside surfaces of the snail target, starting from the very beginning of the laser–target interaction. The time-resolved records of the magnetic field and the electron density distribution inside and outside the snail target characterize the changes in the structure of the magnetized plasma. Inside the target, the magnetic field survives long after the termination of the laser–matter interaction, namely longer than 10 ns. Compared to a circularly polarized laser pulse, the irradiation of targets with a p-polarized beam increases both the emission of hot electrons (HEs) and the intensity of the magnetic field. The emission of HEs is not isotropic, and their energy distribution cannot be characterized by a single temperature.

Optical generators of strong magnetic fields based on the laser-driven-coil target concept are considered to be useful tools for studies of magnetized plasmas in particular, for the study of implosion of magnetized fusion targets in inertial fusion research and astrophysical applications. This paper presents the results of the research directed at an investigation of the plasma properties in a laser-induced magnetic field. In the experiment carried out on the kilojoule PALS laser facility, a generator of the magnetic field was a disc-coil (DC) target composed of a Cu disk coupled to a single-turn coil irradiated by a 1ω laser beam with an energy of 500 J. The attention was focused on examining the influence of the magnetic field on properties of the hot electron (HE) flux emitted from the front surface of the irradiated target. The three-frame complex interferometry and four-frame x-ray camera combined with the measurements of the HE population and energy using a multi-channel magnetic electron spectrometer and 2D-resolved imaging of the induced Cu Kα line emission were applied to characterize the ablative plasma and the generated particles. Based on the measured angular distributions of the electron energy spectra, 3D simulations have been performed to visualize the effect of the magnetic field on the HE flux and to provide information on space-time distribution of the electron and current density both without and with the presence of an axial magnetic field. The obtained results confirmed the possibility of generating magnetic fields above 5 T using the proposed DC target design as well as the significant impact of these fields on properties of the ablative plasma and the HE emission.

The targets that are used to produce high-energy protons with ultra-high intensity lasers generate a strong electromagnetic pulse (EMP). To mitigate that undesired side effect, we developed and tested a concept called the "birdhouse." It consists in confining the EMP field in a finite volume and in dissipating the trapped electromagnetic energy with an electric resistor. A prototype was tested at a 10 TW 50 fs laser facility. The recorded average EMP mitigation ratio is about 20 for frequencies from 100 MHz to 6 GHz. The EMP mitigation ratio attains the level of 50 in the frequency range of 1-2 GHz where microwave emission is maximal. We measured the intensity of proton emission in two directions: along the laser propagation direction and along the edge of the proton beam. We observed that the "birdhouse" induces a two-fold increase of the intensity in the center of the proton beam and a two-fold reduction of the intensity on its edge. We did not observe any modification of the proton beam normalized spectrum.

Extreme Light Infrastructure (ELI) is a large-scale European project, still in the development stage, offering parameters of laser drivers required for multiple applications (femtosecond pulse duration, ultra-relativistic laser intensities ~ 1022 - 1023 W/cm2), however studies of ion acceleration in the given intensity regime are still in the very early stages and require a deeper understanding of the processes occurring during laser-matter interactions to maximize the efficiency of ion acceleration. The purpose of this work is a numerical examination of the properties of carbon ion beams produced during the interaction of an ultra-intense laser beams (of intensities ~ 1021 – 1023 W/cm2 and pulse duration order of femtoseconds, predicted to be available at ELI-NP, Romania) with C12 target. The dependence of ion beam parameters, such as intensity, energy spectrum, maximum and average ion energy and spatial distribution of ion charge density, on laser pulse parameters (mainly intensity) and the target thickness is investigated. The possibility of generation of high intensity, GeV energy ion beams in the foregoing conditions is demonstrated. The obtained results can be useful for research in high energy-density physics, nuclear physics or medical applications of ion beams.