Turbulent hydrodynamics experiments in high energy density plasmas: scientific case and preliminary results of the TurboHEDP project
HIGH POWER LASER SCIENCE AND ENGINEERING 6 (2018) ARTN e44
Experimental platform for the investigation of magnetized-reverse-shock dynamics in the context of POLAR
High Power Laser Science and Engineering Cambridge University Press 6 (2018) e43
Abstract:
The influence of a strong external magnetic field on the collimation of a high Mach number plasma flow and its collision with a solid obstacle is investigated experimentally and numerically. The laser irradiation (I ∼ 2 × 1014 W · cm−2 ) of a multilayer target generates a shock wave that produces a rear side plasma expanding flow. Immersed in a homogeneous 10 T external magnetic field, this plasma flow propagates in vacuum and impacts an obstacle located a few mm from the main target. A reverse shock is then formed with typical velocities of the order of 15–20 ± 5 km/s. The experimental results are compared with 2D radiative magnetohydrodynamic simulations using the FLASH code. This platform allows investigating the dynamics of reverse shock, mimicking the processes occurring in a cataclysmic variable of polar type.Axion-driven cosmic magnetogenesis prior to the QCD crossover
Physical Review Letters American Physical Society 121:2 (2018) 021301
Abstract:
We propose a mechanism for the generation of a magnetic field in the early Universe during the QCD crossover assuming that dark matter is made of axions. Thermoelectric fields arise at pressure gradients in the primordial plasma due to the difference in charge, energy density, and equation of state between the quark and lepton components. The axion field is coupled to the EM field, so when its spatial gradient is misaligned with the thermoelectric field, an electric current is driven. Because of the finite resistivity of the plasma, an electric field appears that is generally rotational. For a QCD axion mass consistent with observational constraints and a conventional efficiency for turbulent dynamo amplification—driven by the same pressure gradients responsible for the thermoelectric fields—a magnetic field is generated on subhorizon scales. After significant Alfvénic unwinding, it reaches a present-day strength of B ∼ 10 − 13 G on a characteristic scale L B ∼ 20 pc . The resulting combination of B L 1 / 2 B is significantly stronger than in any astrophysical scenario, providing a clear test for the cosmological origin of the field through γ -ray observations of distant blazars. The amplitude of the pressure gradients may be inferred from the detection of concomitant gravitational waves, while several experiments are underway to confirm or rule out the existence of axions.Analytical modelling of the expansion of a solid obstacle interacting with a radiative shock
High Power Laser Science and Engineering Cambridge University Press 6 (2018) e30
Abstract:
In this paper, we present a model characterizing the interaction of a radiative shock (RS) with a solid material, as described in a recent paper (Koenig et al., Phys. Plasmas, 24, 082707 (2017)), the new model is then related to recent experiments performed on the GEKKO XII laser facility. The RS generated in a xenon gas cell propagates towards a solid obstacle that is ablated by radiation coming from the shock front and the radiative precursor, mimicking processes occurring in astrophysical phenomena. The model presented here calculates the dynamics of the obstacle expansion, which depends on several parameters, notably the geometry and the temperature of the shock. All parameters required for the model have been obtained from experiments. Good agreement between experimental data and the model is found when spherical geometry is taken into account. As a consequence, this model is a useful and easy tool to infer parameters from experimental data (such as the shock temperature), and also to design future experiments.Measurement of temperature and density using non-collective X-ray Thomson scattering in pulsed power produced warm dense plasmas
Scientific Reports Nature Publishing Group 8 (2018) 8432