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Radiative heat transfer is a fundamental process in high energy density physics and inertial fusion. Accurately predicting the behavior of Marshak waves across a wide range of material properties and drive conditions is crucial for design and analysis of these systems. Conventional numerical solvers and analytical approximations often face challenges in terms of accuracy and computational efficiency. In this work, we propose a novel approach to model Marshak waves using Fourier Neural Operators (FNO). We develop two FNO-based models: (1) a base model that learns the mapping between the drive condition and material properties to a solution approximation based on the widely used analytic model by Hammer & Rosen (2003), and (2) a model that corrects the inaccuracies of the analytic approximation by learning the mapping to a more accurate numerical solution. Our results demonstrate the strong generalization capabilities of the FNOs and show significant improvements in prediction accuracy compared to the base analytic model. [ABSTRACT FROM AUTHOR]

Part II of this special edition contains the remaining 11 papers arising from a Hooke discussion meeting held in March 2020 devoted to exploring the current status of inertial confinement fusion research worldwide and its application to electrical power generation in the future, via the development of an international inertial fusion energy programme. It builds upon increased coordination within Europe over the past decade by researchers supported by the EUROFusion Enabling Research grants, as well as collaborations that have arisen naturally with some of America's and Asia's leading researchers, both in the universities and national laboratories. The articles are devoted to informing an update to the European roadmap for an inertial fusion energy demonstration reactor, building upon the commonalities between the magnetic and inertial fusion communities' approaches to fusion energy. A number of studies devoted to understanding the physics barriers to ignition on current facilities are then presented. The special issue concludes with four state-of-the-art articles describing recent significant advances in fast ignition inertial fusion research. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Solar spicules are small-scale jet-like structures in the lower solar atmosphere. Currently, the formation of these widely distributed structures lacks a complete explanation. It is still unclear whether they play an essential role in corona heating. Here, based on the magnetohydrodynamic scaling transformation relation, we perform experiments with the interaction of a high power laser with a one-dimensional sinusoidal modulated target to model solar spicules. We observe several spicule-like structures with alternating polarity magnetic fields around them. Magnetohydrodynamic simulations with similar parameters show the detail information during the spicules’ formation. The results suggest that the so-called strong pulse model can lead to the formation of the solar spicules. The magnetic reconnection process may also play a part and lead to additional heating and brightening phenomena.

Magnetic reconnection (MR) is a fundamental process in space and laboratory plasmas. The appearance of high power lasers opens a new way to investigate MR under the relativistic condition. In this paper, relativistic collisionless MR driven by two ultra-intense lasers and a pair of asymmetric targets is studied numerically via the kinetic simulations. The static magnetic fields produced by the electron vortex structures with opposite magnetic polarities approach each other driven by the magnetic pressure and the density gradient. The antiparallel magnetic fields annihilate accompanied with the topological variation and the corresponding magnetic field energy is being dissipated to the kinetic energy of the nonthermal charged particles. Besides the outflows along the current sheet, a fast particle bunch is accelerated perpendicularly contributed by the displacement current.

Competition among the two-plasmon decay (TPD) of backscattered light of stimulated Raman scattering (SRS), filamentation of the electron-plasma wave (EPW) and forward side SRS is investigated by two-dimensional particle-in-cell simulations. Our previous work [K. Q. Pan et al., Nucl. Fusion 58, 096035 (2018)] showed that in a plasma with the density near 1/10 of the critical density, the backscattered light would excite the TPD, which results in suppression of the backward SRS. However, this work further shows that when the laser intensity is so high (> 1016 W/cm²) that the backward SRS cannot be totally suppressed, filamentation of the EPW and forward side SRS will be excited. Then the TPD of the backscattered light only occurs in the early stage and is suppressed in the latter stage. Electron distribution functions further show that trapped-particle-modulation instability should be responsible for filamentation of the EPW. This research can promote the understanding of hot-electron generation and SRS saturation in inertial confinement fusion experiments. [ABSTRACT FROM AUTHOR]

Competition among the two-plasmon decay (TPD) of backscattered light of stimulated Raman scattering (SRS), filamentation of the electron-plasma wave (EPW) and forward side SRS is investigated by two-dimensional particle-in-cell simulations. Our previous work [K. Q. Pan et al., Nucl. Fusion 58, 096035 (2018)] showed that in a plasma with the density near 1/10 of the critical density, the backscattered light would excite the TPD, which results in suppression of the backward SRS. However, this work further shows that when the laser intensity is so high ( $>{10}^{16}$ W/cm2) that the backward SRS cannot be totally suppressed, filamentation of the EPW and forward side SRS will be excited. Then the TPD of the backscattered light only occurs in the early stage and is suppressed in the latter stage. Electron distribution functions further show that trapped-particle-modulation instability should be responsible for filamentation of the EPW. This research can promote the understanding of hot-electron generation and SRS saturation in inertial confinement fusion experiments.

The momentum distributions of secondary particles in collisional reactions carry rich information about the interaction dynamics. Traditional spectrometer measurements are always limited to certain aiming directions or a small solid angle. The velocity map imaging device is developed only for certain symmetric momentum distributions, while the reaction microscope is restricted to low count-rate experiments. They all fail in imaging arbitrary momentum distributions of high-intensity particle showers. We propose the momentum computed tomography (MCT) to overcome this situation, which pursues a projection-reconstruction solution to the measurement problem. We lay down the projection theory both in the continuum and discretized forms in the context of a general parameterized MCT model. The reconstruction problem is formulated under the maximum a posteriori framework and the compressed sensing scenario. It is solved with an indefinite preconditioned alternating direction method of multipliers. Numerical experiments are carried out to illustrate the MCT working principles. [ABSTRACT FROM AUTHOR]

In recent years, with the development of megajoule-class laser, to create the physical conditions similar to those of extreme celestial environments in the laboratory has become possible. This makes scientists able to study some important astrophysical processes and physical phenomena in the laboratory. This paper briefly introduces several advances in the high energy density laboratory astrophysics driven by the National Ignition Facility (NIF), including the Rayleigh-Taylor instability in supernova remnants, the collisionless shock wave, the laser inertially-confined fusion detection of the thermonuclear reaction under the stellar core condition, the study of planetary interior state, the study of star formation, etc., which will provide a reference for the scientific experiments in the field of laboratory astrophysics performed by using the Shenguang IV laser facility under construction in China. Finally, the possible scientific issues relevant to the direction of laboratory astrophysics by using the Shenguang IV laser facility in the future are briefly discussed. [ABSTRACT FROM AUTHOR]

This paper deals with the principal results of studies performed by scientists of academic institutes and nuclear industry enterprises in the field of laser physics and high energy density physics. Some projects of creating an advanced experimental laser base are presented, and the directions of works to be done are listed. [ABSTRACT FROM AUTHOR]

The contribution of the USSR Academy of Sciences to the implementation of the Atomic Project is discussed. Examples of scientific, technical, and personnel support by the Academy of Sciences for work on atomic and hydrogen weapons in the Soviet Union are given. The outstanding contribution of scientists of the USSR Academy of Sciences to the creation of nuclear and thermonuclear weapons in our country is noted. The need for close cooperation between RAS scientists and the Rosatom State Corporation is emphasized. [ABSTRACT FROM AUTHOR]

We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH–Br foil drives a $\sim 40$  km/s shock inside a gas cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several millimetres) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time-resolved, point-projection X-ray backlighting ($\sim 20$  μm source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive, allowing to probe the growth of spatial nonuniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive that leads to a collision and stagnation from $\sim 40$  ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility. [ABSTRACT FROM AUTHOR]

Magnetic reconnection driven by laser plasma interactions attracts great interests in the recent decades. Motivated by the rapid development of the laser technology, the ultra strong magnetic field generated by the laser-plasma accelerated electrons provides unique environment to investigate the relativistic magnetic field annihilation and reconnection. It opens a new way for understanding relativistic regimes of fast magnetic field dissipation particularly in space plasmas, where the large scale magnetic field energy is converted to the energy of the nonthermal charged particles. Here we review the recent results in relativistic magnetic reconnection based on the laser and collisionless plasma interactions. The basic mechanism and the theoretical model are discussed. Several proposed experimental setups for relativistic reconnection research are presented. [ABSTRACT FROM AUTHOR]

While major progress has been made in the research of inertial confinement fusion, significant challenges remain in the pursuit of ignition. To tackle the challenges, we propose a double-cone ignition (DCI) scheme, in which two head-on gold cones are used to confine deuterium–tritium (DT) shells imploded by high-power laser pulses. The scheme is composed of four progressive controllable processes: quasi-isentropic compression, acceleration, head-on collision and fast heating of the compressed fuel. The quasi-isentropic compression is performed inside two head-on cones. At the later stage of the compression, the DT shells in the cones are accelerated to forward velocities of hundreds of km s–1. The head-on collision of the compressed and accelerated fuels from the cone tips transfer the forward kinetic energy to the thermal energy of the colliding fuel with an increased density. The preheated high-density fuel can keep its status for a period of approximately 200 ps. Within this period, MeV electrons generated by ps heating laser pulses, guided by a ns laser-produced strong magnetic field further heat the fuel efficiently. Our simulations show that the implosion inside the head-on cones can greatly mitigate the energy requirement for compression; the collision can preheat the compressed fuel of approximately 300 g cm−3 to a temperature above keV. The fuel can then reach an ignition temperature of greater than 5 keV with magnetically assisted heating of MeV electrons generated by the heating laser pulses. Experimental campaigns to demonstrate the scheme have already begun. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'. [ABSTRACT FROM AUTHOR]

Almost 30 years since the last UK nuclear test, it remains necessary regularly to underwrite the safety and effectiveness of the National Nuclear Deterrent. To do so has been possible to date because of the development of continually improving science and engineering tools running on ever more powerful high-performance computing platforms, underpinned by cutting-edge experimental facilities. While some of these facilities, such as the Orion laser, are based in the UK, others are accessed by international collaboration. This is most notably with the USA via capabilities such as the National Ignition Facility, but also with France where a joint hydrodynamics facility is nearing completion following establishment of a Treaty in 2010. Despite the remarkable capability of the science and engineering tools, there is an increasing requirement for experiments as materials age and systems inevitably evolve further from what was specifically trialled at underground nuclear tests (UGTs). The data from UGTs will remain the best possible representation of the extreme conditions generated in a nuclear explosion, but it is essential to supplement these data by realizing new capabilities that will bring us closer to achieving laboratory simulations of these conditions. For high-energy-density physics, the most promising technique for generating temperatures and densities of interest is inertial confinement fusion (ICF). Continued research in ICF by the UK will support the certification of the deterrent for decades to come; hence the UK works closely with the international community to develop ICF science. UK Ministry of Defence © Crown Owned Copyright 2020/AWE. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'. [ABSTRACT FROM AUTHOR]

While plasma often behaves diamagnetically, we demonstrate that the laser irradiation of a thin opaque target with an embedded target-transverse seed magnetic field B _seed can trigger the generation of an order-of-magnitude stronger magnetic field with opposite sign at the target surface. Strong surface field generation occurs when the laser pulse is relativistically intense and results from the currents associated with the cyclotron rotation of laser-heated electrons transiting through the target and the compensating current of cold electrons. We derive a predictive scaling for this surface field generation, B _gen ∼ −2 πB _seed Δ x / λ _0 (in the large spot size limit), where Δ x is the target thickness and λ _0 is the laser wavelength, and conduct 1D and 2D particle-in-cell simulations to confirm its applicability over a wide range of conditions. We additionally demonstrate that both the seed and surface-generated magnetic fields can have a strong impact on application-relevant plasma dynamics, for example substantially altering the overall expansion and ion acceleration from a μ m-thick laser-irradiated target with a kilotesla-level seed magnetic field.

Full impact of one Large Hadron Collider (LHC) 7 TeV proton beam on solid targets made of different materials including copper and carbon, was simulated using an energy deposition code, FLUKA and a two-dimensional hydrodynamic code, BIG2, iteratively. These studies showed that the penetration depth of the entire beam comprised of 2808 proton bunches significantly increases due to a phenomenon named hydrodynamic tunneling of the protons and the shower. For example, the static range of a single 7 TeV proton and its shower is about 1 m in solid copper, but the full LHC beam will penetrate up to about 35 m in the target, if the hydrodynamic effects were included. Due to the potential implications of this result on the machine protection considerations, it was decided to have an experimental verification of the hydrodynamic tunneling effect. For this purpose, experiments were carried out at the CERN HiRadMat (High Radiation to Materials) facility in which extended solid copper cylindrical targets were irradiated with the 440 GeV proton beam generated by the Super Proton Synchrotron (SPS). Simulations of beam-target heating considering the same beam parameters that were used in the experiments, were also performed. These experiments not only confirmed the existence of the hydrodynamic tunneling, but the experimental measurements showed very good agreement with the experimental results as well. This provided confidence in the work on LHC related beam-matter heating simulations. Currently, a design study is being carried out by the international community (with CERN taking the leading role) for a post LHC collider named, the Future Circular Collider (FCC) which will accelerate two counter rotating proton beams up to a particle energy of 50 TeV. Simulations of the full impact of one FCC beam comprised of 10,600 proton bunches with a solid copper target have also been done. These simulations have shown that although the static range of a single 50 TeV proton and its shower in solid copper is around 1.8 m, the entire beam will penetrate up to about 350 m in the target. Feasibility studies of developing a water beam dump for the FCC have also been carried out. A review of this work and its implications on machine protection system are presented in this paper. [ABSTRACT FROM AUTHOR]

Monolithic porous bulk materials have many promising applications ranging from energy storage and catalysis to high energy density physics. High resolution additive manufacturing techniques, such as direct laser writing via two photon polymerization (DLW-TPP), now enable the fabrication of highly porous microlattices with deterministic morphology control. In this work, DLW-TPP is used to print millimeter-sized foam reservoirs (down to 0.06 g cm−3) with tailored density-gradient profiles, where density is varied by over an order of magnitude (for instance from 0.6 to 0.06 g cm−3) along a length of <100 µm. Taking full advantage of this technology, however, is a multiscale materials design problem that requires detailed understanding of how the different length scales, from the molecular level to the macroscopic dimensions, affect each other. The design of these 3D-printed foams is based on the brickwork arrangement of 100 × 100 × 16 µm3 log-pile blocks constructed from sub-micrometer scale features. A block-to-block interdigitated stitching strategy is introduced for obtaining high density uniformity at all length scales. Finally, these materials are used to shape plasma-piston drives during ramp-compression of targets under high energy density conditions created at the OMEGA Laser Facility. [ABSTRACT FROM AUTHOR]

Planetary physics research is an important part of the high energy density ( HED) physics programme at the Facility for Antiprotons and Ion Research ( FAIR) at Darmstadt. In this paper, we report numerical simulations of a proposed experiment named LAboratory PLAnetary Sciences ( LAPLAS). These simulations show that in such experiments, an Fe sample can be imploded to extreme physical conditions that are expected to exist in the interior of the Earth and in the interior of more massive rocky planets named, super-Earths. The LAPLAS experiments will thus provide very valuable information on the equation-of-state ( EOS) and transport properties of HED Fe, which will help the scientists to understand the structure and evolution of the planets in our solar system and of the extrasolar system planets. [ABSTRACT FROM AUTHOR]

The creation of high energy density plasma states produced during laser--solid interaction on a sub-picosecond timescale opens a way to create astrophysical plasmas in the lab to investigate their properties, such as the frequency-dependent refractive index. Available probes to measure absorption and phase-changes given by the complex refractive index of the plasma state are extreme-UV (EUV) and soft X-ray (XUV) ultra-short pulses from high harmonic generation (HHG). For demanding imaging applications such as single-shot measurements of solid density plasmas, the HHG probe has to be optimized in photon number and characterized in intensity and wavefront stability from shot-to-shot. In an experiment, a coherent EUV source based on HHG driven by a compact diode-pumped laser is optimized in photons per pulse for argon and xenon, and the shot-to-shot intensity stability and wavefront changes are characterized. The experimental results are compared to an analytical model estimating the HHG yield, showing good agreement. The obtained values are compared to available data for solid density plasmas to confirm the feasibility of HHG as a probe. [ABSTRACT FROM AUTHOR]

We describe a theoretical approach to calculate the electron impact dynamics of atoms/ions placed in a dense plasma. The model takes into consideration that the continuous electron and the guest atom/ion are affected by a recently proposed (dense) plasma shielding parameter potential. As a test case, the present numerical method is employed to study the electron-impact excitation of He-like Ti XXI by using the distorted-wave wavefunction in the framework of the fully relativistic theory. The finite temperature and density effects as well as solid density plasma effects on the excitation energies, transition properties, and integrated cross sections are discussed in detail, which shed light on the shielding parameter potential in resolving practical problems. Results are compared with the available measurements and previous computations. The present work is not only providing a new implementation of the finite-temperature method by a self-consistent methodology, but also of great interest for the high energy density physics community, i.e., our results are of interest to the fusion researches. • We describe a theoretical approach to calculate the electron impact dynamics of atoms/ions in plasmas. • The finite temperature and density effects on the spectral characteristics are discussed. • This study is of interest for the high-energy density physics community. [ABSTRACT FROM AUTHOR]

Experiments have been done at the CERN HiRadMat (High Radiation to Materials) facility in which large cylindrical copper targets were irradiated with 440 GeV proton beam generated by the Super Proton Synchrotron (SPS). The primary purpose of these experiments was to confirm the existence of hydrodynamic tunneling of ultra-relativistic protons and their hadronic shower in solid materials, that was predicted by previous numerical simulations. The experimental measurements have shown very good agreement with the simulation results. This provides confidence in our simulations of the interaction of the 7 TeV LHC (Large Hadron Collider) protons and the 50 TeV Future Circular Collider (FCC) protons with solid materials, respectively. This work is important from the machine protection point of view. The numerical simulations have also shown that in the HiRadMat experiments, a significant part of the target material is be converted into different phases of High Energy Density (HED) matter, including two–phase solid–liquid mixture, expanded as well as compressed hot liquid phases, two–phase liquid–gas mixture and gaseous state. The HiRadMat facility is therefore a unique ion beam facility worldwide that is currently available for studying the thermophysical properties of HED matter. In the present paper we discuss the numerical simulation results and present a comparison with the experimental measurements. [ABSTRACT FROM AUTHOR]

The physics of astrophysical jets can be divided into three regimes: (i) engine and launch (ii) propagation and collimation, (iii) dissipation and particle acceleration. Since astrophysical jets comprise a huge range of scales and phenomena, practicality dictates that most studies of jets intentionally or inadvertently focus on one of these regimes, and even therein, one body of work may be simply boundary condition for another. We first discuss long standing persistent mysteries that pertain the physics of each of these regimes, independent of the method used to study them. This discussion makes contact with frontiers of plasma astrophysics more generally. While observations theory, and simulations, and have long been the main tools of the trade, what about laboratory experiments? Jet related experiments have offered controlled studies of specific principles, physical processes, and benchmarks for numerical and theoretical calculations. We discuss what has been accomplished on these fronts. Although experiments have indeed helped us to understand certain processes, proof of principle concepts, and benchmarked codes, they have yet to solved an astrophysical jet mystery on their own. A challenge is that experimental tools used for jet-related experiments so far, are typically not machines originally designed for that purpose, or designed with specific astrophysical mysteries in mind. This presents an opportunity for a different way of thinking about the development of future platforms: start with the astrophysical mystery and build an experiment to address it. [ABSTRACT FROM AUTHOR]

A hot relativistic fluid is viewed as a collection of quantum objects that represent interacting elementary particles. We present a conceptual framework for deriving nonlinear equations of motion obeyed by these hypothesized objects. A uniform phenomenological prescription, to affect the quantum transition from a corresponding classical system, is invoked to derive the nonlinear Schrödinger, Klein-Gordon, and Pauli-Schrödinger and Feynman-GellMaan equations. It is expected that the emergent hypothetical nonlinear quantum mechanics would advance, in a fundamental way, both the conceptual understanding and computational abilities, particularly, in the field of extremely high energy-density physics. [ABSTRACT FROM AUTHOR]

High energy lasers are a unique tool to create high pressure states above 10 Mbar at ns time scales, which allow to study material properties under these extreme conditions. These conditions are, for example, comparable with planetary cores, where material properties play an important role for the properties and evolution of a planet. The rapid compression allows also to study dynamic effects of phase transitions as compression times are comparable to relaxation times. We will present recent results of laser compression of iron reaching conditions of so called 'super-Earth' cores. A description of the compression schemes as well as present and future diagnostics is presented. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]