Paul Mabey

High-resolution x-ray radiography (HRXR) is a critical diagnostic tool for studying high-energy-density plasmas in large laser facilities such as the National Ignition Facility, the Laser Mega Joule, and Omega Extended Performance. However, geometric constraints in these facilities pose significant challenges for experimental design. This paper presents a comprehensive characterization of a picosecond laser-driven x-ray source tailored for HRXR applications. Through systematic experimental investigations, we analyzed the influence of various parameters on the performance of the x-ray source, focusing on spatial resolution and spectral distribution across a broad energy range. Our findings reveal that a single thin wire, comparable in diameter to the laser focal spot, positioned at 90° relative to the laser axis, serves as the optimal backlighter configuration. This configuration maximizes spatial resolution and spectral quality, addressing the geometric limitations inherent in large-scale laser facilities. The results provide a robust foundation for designing HRXR experiments, enabling more precise and reliable imaging of high-energy-density plasmas.

Optically-transparent LiF film radiation imaging detectors of three different thicknesses, grown by thermal evaporation on Si(100) substrates and irradiated with monochromatic 7 keV X-rays at several doses in the range between 13 and 4.5×10³ Gy, were investigated by fluorescence microscopy to evaluate their visible photoluminescence response of X-ray induced colour centres and their spatial resolution. By edge-enhancement imaging experiments, performed by irradiating LiF film detectors with an Au mesh in front of them, a spatial resolution of ∼0.3 μm was estimated. This high spatial resolution, combined with the large field of view and the wide dynamic range offered by LiF detectors, encourages their use in X-ray imaging and for high-energy density experiments in synchrotron facilities.

Blast-wave-driven hydrodynamic instabilities are studied in the presence of a background B-field through experiments and simulations in the high-energy-density (HED) physics regime. In experiments conducted at the Laboratoire pour l’utilisation des lasers intenses (LULI), a laser-driven shock-tube platform was used to generate a hydrodynamically unstable interface with a prescribed sinusoidal surface perturbation, and short-pulse x-ray radiography was used to characterize the instability growth with and without a 10-T B-field. The LULI experiments were modeled in FLASH using resistive and ideal magnetohydrodynamics (MHD), and comparing the experiments and simulations suggests that the Spitzer model implemented in FLASH is necessary and sufficient for modeling these planar systems. These results suggest insufficient amplification of the seed B-field, due to resistive diffusion, to alter the hydrodynamic behavior. Although the ideal-MHD simulations did not represent the experiments accurately, they suggest that similar HED systems with dynamic plasma-β (=2μ₀ρv²/B²) values of less than ∼100 can reduce the growth of blast-wave-driven Rayleigh–Taylor instabilities. These findings validate the resistive-MHD FLASH modeling that is being used to design future experiments for studying B-field effects in HED plasmas.

A new method of calculating the temperature of strongly radiative shocks (Mihalas number of order unity or lower) is proposed. By including ionization, radiative energy, and radiative flux terms in the Rankine–Hugoniot jump conditions across the shock front, a new, self-consistent method of calculating the temperature of radiative shocks is developed. The method is compared to those used to calculate temperature in previous studies using similar methods, including those which partially included radiative and/or ionization effects. The method is also compared to experimental data, taken from the literature, as well as the SESAME equation of state tables and radiative hydrodynamics simulations. The results show the importance of including all radiative terms for the case of strongly radiative shocks. This result has important implications for the design and interpretation of future laboratory experiments where even faster radiative shocks may be generated. Previously unseen phenomena could be accessible when the radiative energy plays a significant role in the system.

Many supernova remnants (SNRs), such as G296.5+10.0, exhibit an axisymmetric or barrel shape. Such morphologies have previously been linked to the direction of the Galactic magnetic field, although this remains uncertain. These SNRs generate magnetohydrodynamic shocks in the interstellar medium, modifying its physical and chemical properties. The ability to study these shocks through observations is difficult due to the small spatial scales involved. In order to answer these questions, we perform a scaled laboratory experiment in which a laser-generated blast wave expands under the influence of a uniform magnetic field. The blast wave exhibits a spheroidal shape, whose major axis is aligned with the magnetic field, in addition to a more continuous shock front. The implications of our results are discussed in the context of astrophysical systems.

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jet winds, etc.) is a common process which leads to a more intricate structure of the interstellar medium. In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNRs) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage, and the distance between the two stars. In this Letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BWs) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼500 J) of 300 μm diameter carbon rods and propagate in different gases (Ar and N₂) at different pressures. The physical parameters, such as the density and temperature of the IR, are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy, etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17–20% increase in temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long periods after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.

We develop a new approach to modeling many-body systems based on Bohm’s interpretation of quantum mechanics.

The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of photon energy with no saturation level found. The response, as a function of the incident energy flux, is found to increase for photons of lower energy due to the differing attenuation lengths of X-ray photons within the crystal. Small differences are seen between different confocal microscopes used to scan the data, suggesting the need for absolute calibration. The spatial resolution of the LiF is also measured (1.19–1.36 μm) and is found to be independent of incident photon energy. Finally, a photometric study is performed in order to assess the feasibility of using these detectors at current X-ray free electron laser and laser facilities worldwide.

The properties of supersonic, compressible plasma turbulence determine the behavior of many terrestrial and astrophysical systems. In the interstellar medium and molecular clouds, compressible turbulence plays a vital role in star formation and the evolution of our galaxy. Observations of the density and velocity power spectra in the Orion B and Perseus molecular clouds show large deviations from those predicted for incompressible turbulence. Hydrodynamic simulations attribute this to the high Mach number in the interstellar medium (ISM), although the exact details of this dependence are not well understood. Here we investigate experimentally the statistical behavior of boundary-free supersonic turbulence created by the collision of two laser-driven high-velocity turbulent plasma jets. The Mach number dependence of the slopes of the density and velocity power spectra agree with astrophysical observations, and supports the notion that the turbulence transitions from being Kolmogorov-like at low Mach number to being more Burgers-like at higher Mach numbers.