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

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences The Royal Society 379 (2020) 20200028

P Norreys, C Ridgers, K Lancaster, M Koepke, G Tynan

Part II of this special edition contains the remaining eleven 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.

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

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences The Royal Society 379 (2020) 20200224

R Paddock, H Martin, R Ruskov, R Scott, W Garbett, B Haines, A Zylstra, R Aboushelbaya, M Mayr, B Spiers, R Wang, P Norreys

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.

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

Philosophical transactions. Series A, Mathematical, physical, and engineering sciences 379 (2021) 20200039-

E Boella, R Bingham, RA Cairns, P Norreys, R Trines, R Scott, M Vranic, N Shukla, LO Silva

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)'.

Whole-beam self-focusing in fusion-relevant plasma

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences Royal Society 379 (2020) 20200159

B Spiers, M Hill, C Brown, L Ceurvorst, N Ratan, A Savin, P Allan, E Floyd, J Fyrth, L Hobbs, S James, J Luis, M Ramsay, N Sircombe, J Skidmore, R Aboushelbaya, M Mayr, R Paddock, R Wang, P Norreys

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 characterisation 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 fullscale particle-in-cell simulations. We present observations of long lived, straight channels produced by the Habara-Kodama-Tanaka (HKT) wholebeam self-focusing mechanism, overcoming a critical barrier on the path to realising fast ignition.

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

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences The Royal Society 379 (2020) 20200005

P Norreys, L Ceurvorst, J Sadler, B Spiers, M Mayr, N Ratan, A Savin, K Glize, R Trines, B Bingham, M Hill, N Sircombe, P Allan, L Hobbs, S James, J Skidmore, J Fyrth, J Luis, E Floyd, C Brown, B Haines, R Olson, S Yi, A Zylstra, R Peterson

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.

Increasing the brightness of harmonic XUV radiation with spatially-tailored driver beams

Journal of Optics IOP Publishing 23 (2020) 015502

D Treacher, D Lloyd, K O’Keeffe, F Wiegandt, S Hooker

Bright high harmonic sources can be produced by loosely focussing high peak power laser pulses to exploit the quadratic scaling of flux with driver spot size at the expense of a larger experimental footprint. Here, we present a method for increasing the brightness of a harmonic source (while maintaining a compact experimental geometry) by spatially shaping the transverse focal intensity distribution of a driving laser from a Gaussian to supergaussian. Using a phase-only spatial light modulator we increase the size and order of the supergaussian focal profiles, thereby increasing the number of harmonic emitters more efficiently than possible with Gaussian beams. This provides the benefits of a loose focussing geometry, yielding a five-fold increase in harmonic brightness, whilst maintaining a constant experimental footprint. This technique can readily be applied to existing high harmonic systems, opening new opportunities for applications requiring bright, compact sources of coherent short wavelength radiation.

First demonstration of ARC-accelerated proton beams at the National Ignition Facility (vol 26, 043110, 2019)

PHYSICS OF PLASMAS 27 (2020) ARTN 129901

D Mariscal, T Ma, SC Wilks, AJ Kemp, GJ Williams, P Michel, H Chen, PK Patel, BA Remington, M Bowers, L Pelz, MR Hermann, W Hsing, D Martinez, R Sigurdsson, M Prantil, A Conder, J Lawson, M Hamamoto, P Di Nicola, C Widmayer, D Hoemoelle, R Lowe-Webb, S Herriot, W Williams, D Alessi, D Kalantar, R Zacharias, C Haefner, N Thompson, T Zobrist, D Lord, N Hash, A Pak, N Lemos, M Tabak, C McGuffey, J Kim, FN Beg, MS Wei, P Norreys, A Morace, N Iwata, Y Sentoku, D Neely, GG Scott, K Flippo, M Gatu-Johnson, B Lahmann

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

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences The Royal Society 378 (2020) 20200006

P Norreys, K Lancaster, C Ridgers, M Koepke, G Tynan

Electron trapping and reinjection in prepulse-shaped gas targets for laser-plasma accelerators

Physical Review Accelerators and Beams American Physical Society (APS) 23 (2020) 111301

R Scott, C Thornton, N Bourgeois, J Cowley, W Rittershofer, T Kleinwächter, J Osterhoff, D Symes, C Hooker, S Hooker

Meter-scale conditioned hydrodynamic optical-field-ionized plasma channels

Physical Review E American Physical Society (APS) 102 (2020) 53201

A Picksley, A Alejo, R Shalloo, C Arran, A von Boetticher, L Corner, J Holloway, J Jonnerby, O Jakobsson, C Thornton, R Walczak, S Hooker

We demonstrate through experiments and numerical simulations that low-density, low-loss, meter-scale plasma channels can be generated by employing a conditioning laser pulse to ionize the neutral gas collar surrounding a hydrodynamic optical-field-ionized (HOFI) plasma channel. We use particle-in-cell simulations to show that the leading edge of the conditioning pulse ionizes the neutral gas collar to generate a deep, low-loss plasma channel which guides the bulk of the conditioning pulse itself as well as any subsequently injected pulses. In proof-of-principle experiments we generate conditioned HOFI (CHOFI) waveguides with axial electron densities of $n_\mathrm{e0} \approx 1 \times 10^{17} \; \mathrm{cm^{-3}}$, and a matched spot size of $26 \; \mathrm{\mu m}$. The power attenuation length of these CHOFI channels is $L_\mathrm{att} = (21 \pm 3) \; \mathrm{m}$, more than two orders of magnitude longer than achieved by HOFI channels. Hydrodynamic and particle-in-cell simulations demonstrate that meter-scale CHOFI waveguides with attenuation lengths exceeding 1 m could be generated with a total laser pulse energy of only $1.2$ J per meter of channel. The properties of CHOFI channels are ideally suited to many applications in high-intensity light-matter interactions, including multi-GeV plasma accelerator stages operating at high pulse repetition rates.

Numerical modelling of chromatic effects on axicon-focused beams used to generate HOFI plasma channels

Journal of Physics: Conference Series IOP Publishing 1596 (2020)

A Ross, A Alejo, A von Boetticher, J Cowley, J Holloway, J Jonnerby, A Picksley, R Walczak, S Hooker

Hydrodynamic optical-field-ionised (HOFI) plasma channels promise a route towards high repetition-rate, metre-scale stages for future laser plasma accelerators. These channels are formed by hydrodynamic expansion of a plasma column produced by optical field ionisation at the focus of a laser, typically from an axicon lens. Since the laser pulses used to generate the initial plasma column are of sub-picosecond duration, chromatic effects in the axicon lens could be important. In this paper we assess these effects using a numerical propagation code. The code is validated using analytical formulae and experimental data. For the parameter range investigated, dispersive effects are found to be of minor importance, reducing the peak on-axis intensity in the focal region by approximately 10%.

Nonlinear wakefields and electron injection in cluster plasma

Physical Review Accelerators and Beams American Physical Society 23 (2020) 093501

M Mayr, B Spiers, R Aboushelbaya, R Paddock, J Sadler, C Sillett, R Wang, K Krushelnick, P Norreys

Laser and beam driven wakefields promise orders of magnitude increases in electric field gradients for particle accelerators for future applications. Key areas to explore include the emittance properties of the generated beams and overcoming the dephasing limit in the plasma. In this paper, the first in-depth study of the self-injection mechanism into wakefield structures from nonhomogeneous cluster plasmas is provided using high-resolution two dimensional particle-in-cell simulations. The clusters which are typical structures caused by ejection of gases from a high-pressure gas jet have a diameter much smaller than the laser wavelength. Conclusive evidence is provided for the underlying mechanism that leads to particle trapping, comparing uniform and cluster plasma cases. The accelerated electron beam properties are found to be tunable by changing the cluster parameters. The mechanism explains enhanced beam charge paired with large transverse momentum and energy which has implications for the betatron x-ray flux. Finally, the impact of clusters on the high-power laser propagation behavior is discussed.

Bright x-ray radiation from plasma bubbles in an evolving laser wakefield accelerator

Physical Review Accelerators and Beams 23 (2020)

MS Bloom, MJV Streeter, S Kneip, RA Bendoyro, O Cheklov, JM Cole, A Döpp, CJ Hooker, J Holloway, J Jiang, NC Lopes, H Nakamura, PA Norreys, PP Rajeev, DR Symes, J Schreiber, JC Wood, M Wing, Z Najmudin, SPD Mangles

© 2020 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the ""Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. We show that the properties of the electron beam and bright x rays produced by a laser wakefield accelerator can be predicted if the distance over which the laser self-focuses and compresses prior to self-injection is taken into account. A model based on oscillations of the beam inside a plasma bubble shows that performance is optimized when the plasma length is matched to the laser depletion length. With a 200 TW laser pulse, this results in an x-ray beam with a median photon energy of 20 keV, >6×108 photons above 1 keV per shot, and a peak brightness of 3×1022 photons s-1 mrad-2 mm-2 (0.1% BW)-1.

Measuring the orbital angular momentum of high-power laser pulses

Physics of Plasmas AIP Publishing 27 (2020) 053107

R Aboushelbaya, K Glize, A Savin, M Mayr, B Spiers, R Wang, N Bourgeois, C Spindloe, R Bingham, P Norreys

In this article, we showcase the experimental results of methods to produce and characterize orbital angular momentum (OAM) carrying high-power lasers. The OAM pulses were produced on the ASTRA laser of the Central Laser Facility using a continuous spiral phase plate. Three different characterization methods were then used to measure the OAM content of the beam. The methods that were used were a cylindrical lens diagnostic, an interferometric diagnostic, and a projective diagnostic. We further discuss the relative advantages and disadvantages of each method in the context of high-power laser experiments.

Nonlinear plasma wavelength scalings in a laser wakefield accelerator

Physical Review E American Physical Society 101 (2020) 23209

H Ding, A Döpp, M Gilljohann, J Götzfried, S Schindler, L Wildgruber, G Cheung, SM Hooker, S Karsch

Laser wakefield acceleration relies on the excitation of a plasma wave due to the ponderomotive force of an intense laser pulse. However, plasma wave trains in the wake of the laser have scarcely been studied directly in experiments. Here we use few-cycle shadowgraphy in conjunction with interferometry to quantify plasma waves excited by the laser within the density range of GeV-scale accelerators, i.e., a few 10(18)cm−3. While analytical models suggest a clear dependency between the nonlinear plasma wavelength and the peak potential a0, our study shows that the analytical models are only accurate for driver strength a 0≲1. Experimental data and systematic particle-in-cell simulations reveal that nonlinear lengthening of the plasma wave train depends not solely on the laser peak intensity but also on the waist of the focal spot.

Eupraxia, a step toward a plasma-wakefield based accelerator with high beam quality

Journal of Physics: Conference Series IOP Science 1350 (2019)

D Alesini, A Aschikhin, A Beck, M Chen, E Chiadroni, M Croia, B Cros, A Del Dotto, M Ferrario, RA Fonseca, LA Gizzi, SM Hooker, L Labate, A Martinez De La Ossa, A Mosnier, A Mostacci, D Oumbarek Espinos, A Stella, EN Svystun, D Terzani, P Tomassini, JM Vieira, CP Welsch, SM Wiggins, J Wolfenden

The EuPRAXIA project aims at designing the world's first accelerator based on advanced plasma-wakefield techniques to deliver 5 GeV electron beams that simultaneously have high charge, low emittance and low energy spread, which are required for applications by future user communities. Meeting this challenging objective will only be possible through dedicated effort. Many injection/acceleration schemes and techniques have been explored by means of thorough simulations in more than ten European research institutes. This enables selection of the most appropriate methods for solving each particular problem. The specific challenge of generating, extracting and transporting high charge beams, while maintaining the high quality needed for user applications, are being tackled using innovative approaches. This article highlights preliminary results obtained by the EuPRAXIA collaboration, which also exhibit the required laser and plasma parameters.

Wakefields in a cluster plasma

Physical Review Special Topics: Accelerators and Beams American Physical Society 22 (2019) 113501

M Mayr, L Ceurvorst, M Kasim, J Sadler, B Spiers, K Glize, A Savin, N Bourgeois, F Keeble, A Ross, D Symes, R Aboushelbaya, R Fonseca, J Holloway, N Ratan, R Trines, R Wang, R Bingham, P Burrows, M Wing, R Pattathil, P Norreys

We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.

EuPRAXIA – a compact, cost-efficient particle and radiation source

AIP Conference Proceedings AIP Publishing 2160 (2019)

MK Weikum, T Akhter, PD Alesini, S Hooker, R Walczak

Plasma accelerators present one of the most suitable candidates for the development of more compact particle acceleration technologies, yet they still lag behind radiofrequency (RF)-based devices when it comes to beam quality, control, stability and power efficiency. The Horizon 2020-funded project EuPRAXIA (“European Plasma Research Accelerator with eXcellence In Applications”) aims to overcome the first three of these hurdles by developing a conceptual design for a first international user facility based on plasma acceleration. In this paper we report on the main features, simulation studies and potential applications of this future research infrastructure.

Optimised XUV holography using spatially shaped high harmonic beams

Optics Express The Optical Society 27 (2019) 29016-29016

DJ Treacher, DT Lloyd, F Wiegandt, K O’Keeffe, SM Hooker

Orbital angular momentum coupling in elastic photon-photon scattering

Physical Review Letters American Physical Society 123 (2019) 113604

R Aboushelbaya, K Glize, A Savin, M Mayr, B Spiers, R Wang, J Collier, M Marklund, R Trines, R Bingham, P Norreys

In this Letter, we investigate the effect of orbital angular momentum (OAM) on elastic photon-photon scattering in a vacuum for the first time. We define exact solutions to the vacuum electromagnetic wave equation which carry OAM. Using those, the expected coupling between three initial waves is derived in the framework of an effective field theory based on the Euler-Heisenberg Lagrangian and shows that OAM adds a signature to the generated photons thereby greatly improving the signal-to-noise ratio. This forms the basis for a proposed high-power laser experiment utilizing quantum optics techniques to filter the generated photons based on their OAM state.