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Wehrenberg et al [Nature 550 496 (2017)] used ultrafast in situ x-ray diffraction at the LCLS xray free-electron laser facility to measure large lattice rotations resulting from slip and deformation twinning in shock-compressed laser-driven [110] fibre textured tantalum polycrystal. We employ a crystal plasticity finite element method model, with slip kinetics based closely on the isotropic dislocation-based Livermore Multiscale Model [Barton et al., J. Appl. Phys. 109 (2011)], to analyse this experiment. We elucidate the link between the degree of lattice rotation and the kinetics of plasticity, demonstrating that a transition occurs at shock pressures of ∼27 GPa, between a regime of relatively slow kinetics, resulting in a balanced pattern of slip system activation and therefore relatively small net lattice rotation, and a regime of fast kinetics, due to the onset of nucleation, resulting in a lop-sided pattern of deformation-system activation and therefore large net lattice rotations. We demonstrate a good fit between this model and experimental x-ray diffraction data of lattice rotation, and show that this data is constraining of deformation kinetics.

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. A brief overview of these activities, presented here, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Fast ignition inertial confinement fusion requires the production of a low-density channel in plasma with density scale-lengths of several hundred microns. The channel assists in the propagation of an ultra-intense laser pulse used to generate fast electrons which form a hot spot on the side of pre-compressed fusion fuel. We present a systematic characterization of an expanding laser-produced plasma using optical interferometry, benchmarked against three-dimensional hydrodynamic simulations. Magnetic fields associated with channel formation are probed using proton radiography, and compared to magnetic field structures generated in full-scale particle-in-cell simulations. We present observations of long-lived, straight channels produced by the Habara–Kodama–Tanaka whole-beam self-focusing mechanism, overcoming a critical barrier on the path to realizing fast ignition. This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

We report a new method using high-stability, laser-driven supercontinuum generation in a liquid cell to calibrate the absolute photon response of fast optical streak cameras as a function of wavelength when operating at fastest sweep speeds. A stable, pulsed white light source based around the use of self-phase modulation in a salt solution was developed to provide the required brightness on picosecond time scales, enabling streak camera calibration in fully dynamic operation. The measured spectral brightness allowed for absolute photon response calibration over a broad spectral range (425-650 nm). Calibrations performed with two Axis Photonique streak cameras using the Photonis P820PSU streak tube demonstrated responses that qualitatively follow the photocathode response. Peak sensitivities were one photon/count above background. The absolute dynamic sensitivity is less than the static by up to an order of magnitude. We attribute this to the dynamic response of the phosphor being lower.