High Gain Inertial Fusion Energy Research Articles

Prospects for high gain inertial fusion energy: an introduction to the second edition.

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)'.

One-dimensional hydrodynamic simulations of low convergence ratio direct-drive inertial confinement fusion implosions.

Indirect drive inertial confinement fusion experiments with convergence ratios below 17 have been previously shown to be less susceptible to Rayleigh–Taylor hydrodynamic instabilities, making this regime highly interesting for fusion science. Additional limitations imposed on the implosion velocity, in-flight aspect ratio and applied laser power aim to further reduce instability growth, resulting in a new regime where performance can be well represented by one-dimensional (1D) hydrodynamic simulations. A simulation campaign was performed using the 1D radiation-hydrodynamics code HYADES to investigate the performance that could be achieved using direct-drive implosions of liquid layer capsules, over a range of relevant energies. Results include potential gains of 0.19 on LMJ-scale systems and 0.75 on NIF-scale systems, and a reactor-level gain of 54 for an 8.5 MJ implosion. While the use of 1D simulations limits the accuracy of these results, they indicate a sufficiently high level of performance to warrant further investigations and verification of this new low-instability regime. This potentially suggests an attractive new approach to fusion energy.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Sources and space-time distribution of the electromagnetic pulses in experiments on inertial confinement fusion and laser-plasma acceleration.

When high-energy and high-power lasers interact with matter, a significant part of the incoming laser energy is transformed into transient electromagnetic pulses (EMPs) in the range of radiofrequencies and microwaves. These fields can reach high intensities and can potentially represent a significative danger for the electronic devices placed near the interaction point. Thus, the comprehension of the origin of these electromagnetic fields and of their distribution is of primary importance for the safe operation of high-power and high-energy laser facilities, but also for the possible use of these high fields in several promising applications. A recognized main source of EMPs is the target positive charging caused by the fast-electron emission due to laser-plasma interactions. The fast charging induces high neutralization currents from the conductive walls of the vacuum chamber through the target holder. However, other mechanisms related to the laser-target interaction are also capable of generating intense electromagnetic fields. Several possible sources of EMPs are discussed here and compared for high-energy and high-intensity laser-matter interactions, typical for inertial confinement fusion and laser-plasma acceleration. The possible effects on the electromagnetic field distribution within the experimental chamber, due to particle beams and plasma emitted from the target, are also described. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Recent progress in quantifying hydrodynamics instabilities and turbulence in inertial confinement fusion and high-energy-density experiments.

Since the seminal paper of Nuckolls triggering the quest of inertial confinement fusion (ICF) with lasers, hydrodynamic instabilities have been recognized as one of the principal hurdles towards ignition. This remains true nowadays for both main approaches (indirect drive and direct drive), despite the advent of MJ scale lasers with tremendous technological capabilities. From a fundamental science perspective, these gigantic laser facilities enable also the possibility to create dense plasma flows evolving towards turbulence, being magnetized or not. We review the state of the art of nonlinear hydrodynamics and turbulent experiments, simulations and theory in ICF and high-energy-density plasmas and draw perspectives towards in-depth understanding and control of these fascinating phenomena. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Preparations for a European R&D roadmap for an inertial fusion demo reactor.

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)’.

The inadequacy of a magnetohydrodynamic approach to the Biermann battery.

Magnetic fields can be generated in plasmas by the Biermann battery when the electric field produced by the electron pressure gradient has a curl. The commonly employed magnetohydrodynamic (MHD) model of the Biermann battery breaks down when the electron distribution function is distorted away from Maxwellian. Using both MHD and kinetic simulations of a laser-plasma interaction relevant to inertial confinement fusion we have shown that this distortion can reduce the Biermann-producing electric field by around 50%. More importantly, the use of a flux limiter in an MHD treatment to deal with the effect of the non-Maxwellian electron distribution on electron thermal transport leads to a completely unphysical prediction of the Biermann-producing electric field and so results in erroneous predictions for the generated magnetic field.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Direct-drive laser fusion: status, plans and future.

Laser-direct drive (LDD), along with laser indirect (X-ray) drive (LID) and magnetic drive with pulsed power, is one of the three viable inertial confinement fusion approaches to achieving fusion ignition and gain in the laboratory. The LDD programme is primarily being executed at both the Omega Laser Facility at the Laboratory for Laser Energetics and at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory. LDD research at Omega includes cryogenic implosions, fundamental physics including material properties, hydrodynamics and laser-plasma interaction physics. LDD research on the NIF is focused on energy coupling and laser-plasma interactions physics at ignition-scale plasmas. Limited implosions on the NIF in the 'polar-drive' configuration, where the irradiation geometry is configured for LID, are also a feature of LDD research. The ability to conduct research over a large range of energy, power and scale size using both Omega and the NIF is a major positive aspect of LDD research that reduces the risk in scaling from OMEGA to megajoule-class lasers. The paper will summarize the present status of LDD research and plans for the future with the goal of ultimately achieving a burning plasma in the laboratory. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Whole-beam self-focusing in fusion-relevant plasma.

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)’.

Collisionless shock acceleration in the corona of an inertial confinement fusion pellet with possible application to ion fast ignition.

Two-dimensional particle-in-cell simulations are used to explore collisionless shock acceleration in the corona plasma surrounding the compressed core of an inertial confinement fusion pellet. We show that an intense laser pulse interacting with the long scale-length plasma corona is able to launch a collisionless shock around the critical density. The nonlinear wave travels up-ramp through the plasma reflecting and accelerating the background ions. Our results suggest that protons with characteristics suitable for ion fast ignition may be achieved in this way.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

An overview of shared technical challenges for magnetic and inertial fusion power plant development.

Fusion energy is an area of active development and innovation worldwide, with many design concepts studied, each exhibiting a range of technical challenges. A significant portion of technical challenges will be unique for a given design concept; however, there are several overarching challenges that any design must address to some degree. These include tritium handling and the tritium cycle; materials and their survivability in the high-energy neutron environment of D-T fusion; neutronics and the validation of nuclear data; remote handling and maintenance activities; and integrated holistic approaches to fusion plant design. This paper provides an overview of these aspects for magnetic and inertial fusion approaches with a view to highlighting commonality and the benefits of shared knowledge that this may bring. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Factors influencing the commercialization of inertial fusion energy.

Managing the IFE pathway to fusion electricity will involve management of commericalization scope, schedule, cost and risk. The technology pathway to economical fusion power comprises the commercialization scope. Industry assumes commercialization risk in fielding its own pre-pilot plant research programme for this compact-fusion pathway without the benefit of a federally coordinated IFE research and development programme. The cost of commercializing the mass-production of inexpensive targets and insisting on high reliability, availability, maintainability and inspectability has a major impact on the economics of commercializing fusion power plants. Schedule vulnerability for inertial fusion energy arises from the sensitivity of time-based roadmap stages to uncertainties in the pace of scientific understanding and technology development, as well as to unexpected and inexplicable changes of the budgeting process. Rather than rely on a time-based roadmap, a milestone-based roadmap is maximally appropriate, especially for industry and investors who are particularly well-suited to taking the risks associated with reaching the target milestones provided by the government. Milestones must be identified and optimally sequenced and the necessary resources must be delineated. Progress on the above factors, since the outcomes of recent U.S., U.K. and EUROfusion roadmapping exercises were released, are reported. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Fast electron transport dynamics and energy deposition in magnetized, imploded cylindrical plasma.

Inertial confinement fusion approaches involve the creation of high-energy-density states through compression. High gain scenarios may be enabled by the beneficial heating from fast electrons produced with an intense laser and by energy containment with a high-strength magnetic field. Here, we report experimental measurements from a configuration integrating a magnetized, imploded cylindrical plasma and intense laser-driven electrons as well as multi-stage simulations that show fast electrons transport pathways at different times during the implosion and quantify their energy deposition contribution. The experiment consisted of a CH foam cylinder, inside an external coaxial magnetic field of 5 T, that was imploded using 36 OMEGA laser beams. Two-dimensional (2D) hydrodynamic modelling predicts the CH density reaches , the temperature reaches 920 eV and the external B-field is amplified at maximum compression to 580 T. At pre-determined times during the compression, the intense OMEGA EP laser irradiated one end of the cylinder to accelerate relativistic electrons into the dense imploded plasma providing additional heating. The relativistic electron beam generation was simulated using a 2D particle-in-cell (PIC) code. Finally, three-dimensional hybrid-PIC simulations calculated the electron propagation and energy deposition inside the target and revealed the roles the compressed and self-generated B-fields play in transport. During a time window before the maximum compression time, the self-generated B-field on the compression front confines the injected electrons inside the target, increasing the temperature through Joule heating. For a stronger B-field seed of 20 T, the electrons are predicted to be guided into the compressed target and provide additional collisional heating.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 2)’.

Prospects for high gain inertial fusion energy: an introduction to the first special edition.

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. The Hooke discussion meeting in March 2020 provided an opportunity to reflect on the progress made in inertial confinement fusion research world-wide to date. This first edition of two special issues seeks to identify paths forward to achieve high fusion energy gain.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.

Modelling burning thermonuclear plasma.

Considerable progress towards the achievement of thermonuclear burn using inertial confinement fusion has been achieved at the National Ignition Facility in the USA in the last few years. Other drivers, such as the Z-machine at Sandia, are also making progress towards this goal. A burning thermonuclear plasma would provide a unique and extreme plasma environment; in this paper we discuss (a) different theoretical challenges involved in modelling burning plasmas not currently considered, (b) the use of novel machine learning-based methods that might help large facilities reach ignition, and (c) the connections that a burning plasma might have to fundamental physics, including quantum electrodynamics studies, and the replication and exploration of conditions that last occurred in the first few minutes after the Big Bang. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

The importance of the laser pulse-ablator interaction dynamics prior to the ablation plasma phase in inertial confinement fusion studies.

This work presents studies which demonstrate the importance of the very early heating dynamics of the ablator long before the ablation plasma phase begins in laser driven inertial confinement fusion (ICF) studies. For the direct-drive fusion concept using lasers, the development of perturbations during the thermo-elasto-plastic (TEP) and melting phases of the interaction of the laser pulse with the ablator's surface may act as seeding to the subsequent growth of hydro-dynamic instabilities apparent during the acceleration phase of the interaction such as for instance the Rayleigh-Taylor and the Richtmyer-Meshkov, which strongly affect the implosion dynamics of the compression phase. The multiphysics-multiphase finite-element method (FEM) simulation results are experimentally validated by advanced three-dimensional whole-field dynamic imaging of the surface of the ablator allowing for a transverse to the surface spatial resolution of only approximately 1 nm. The study shows that the TEP and melting phases of the interaction are of crucial importance since transverse perturbations of the ablator's surface can reach tens of nanometres in amplitude within the TEP and melting phases. Such perturbations are of Rayleigh type and are transferred from the ablator to the substrate from the very first moments of the interaction. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Magnetic field generation from composition gradients in inertial confinement fusion fuel.

Experimental asymmetries in fusion implosions can lead to magnetic field generation in the hot plasma core. For typical parameters, previous studies found that the magnetization Hall parameter, given by the product of the electron gyro-frequency and Coulomb collision time, can exceed one. This will affect the hydrodynamics through inhibition and deflection of the electron heat flux. The magnetic field source is the collisionless Biermann term, which arises from the Debye shielding potential in electron pressure gradients. We show that there is an additional source term due to the Z dependence of the Coulomb collision operator. If there are ion composition gradients, such as jets of carbon ablator mix entering the hot-spot, this source term can rapidly exceed the Biermann fields. In addition, the Biermann fields are enhanced due to the increased temperature gradients from carbon radiative cooling. With even stronger self-generated fields, heat loss to the carbon regions will be reduced, potentially reducing the negative effect of carbon mix. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 1)'.

Inertial confinement fusion: a defence context.

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)'.

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy.

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% ‘wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)'.

Progress and opportunities for inertial fusion energy in Europe.

In this paper, I consider the motivations, recent results and perspectives for the inertial confinement fusion (ICF) studies in Europe. The European approach is based on the direct drive scheme with a preference for the central ignition boosted by a strong shock. Compared to other schemes, shock ignition offers a higher gain needed for the design of a future commercial reactor and relatively simple and technological targets, but implies a more complicated physics of laser–target interaction, energy transport and ignition. European scientists are studying physics issues of shock ignition schemes related to the target design, laser plasma interaction and implosion by the code developments and conducting experiments in collaboration with US and Japanese physicists, providing access to their installations Omega and Gekko XII. The ICF research in Europe can be further developed only if European scientists acquire their own academic laser research facility specifically dedicated to controlled fusion energy and going beyond ignition to the physical, technical, technological and operational problems related to the future fusion power plant. Recent results show significant progress in our understanding and simulation capabilities of the laser plasma interaction and implosion physics and in our understanding of material behaviour under strong mechanical, thermal and radiation loads. In addition, growing awareness of environmental issues has attracted more public attention to this problem and commissioning at ELI Beamlines the first high-energy laser facility with a high repetition rate opens the opportunity for qualitatively innovative experiments. These achievements are building elements for a new international project for inertial fusion energy in Europe.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.

Crossed beam energy transfer between optically smoothed laser beams in inhomogeneous plasmas.

Crossed beam energy transfer, CBET, in high-intensity laser–plasma interaction is investigated for the case of optically smoothed laser beams. In the two approaches to laser-driven inertial confinement fusion experiments, the direct-drive and the indirect-drive, CBET is of great importance because it governs the coupling of laser energy to the plasma. We use the two-dimensional wave-coupling code Harmony to simulate the transfer between two laser beams with speckle structure that overlap in a plasma with an inhomogeneous flow profile. We compare the CBET dynamics for laser beams with spatial incoherence and with spatio-temporal incoherence; in particular we apply the smoothing techniques using random phase plates (RPPs) and smoothing by spectral dispersion (SSD), respectively. It is found that for laser beams (wavelength λ0) with intensities (IL) above IL ∼ 2 × 1015 W cm−2(λ0/0.35 µm)−2(Te/keV), both the so-called plasma-induced smoothing as well as self-focusing in intense laser speckles induce temporal incoherence; the latter affects the CBET and the angular distribution of the light transmitted behind the zone of beam overlap. For RPP-smoothed incident beams, the resulting band width of the transmitted light can already be of the same order as the effective band width of the SSD available at major laser facilities. We examine the conditions when spatio-temporal smoothing techniques become efficient for CBET.This article is part of a discussion meeting issue ‘Prospects for high gain inertial fusion energy (part 1)’.