Publications


Axion detection through resonant photon-photon collisions

Physical Review D American Physical Society (APS) 101 (2020) 95018

K Beyer, G Marocco, R Bingham, G Gregori


Transport of high-energy charged particles through spatially-intermittent turbulent magnetic fields

Astrophysical Journal American Astronomical Society 892 (2020) 114

LE Chen, AFA Bott, P Tzeferacos, A Rigby, A Bell, R Bingham, C Graziani, J Katz, R Petrasso, G Gregori, F Miniati

Identifying the sources of the highest energy cosmic rays requires understanding how they are deflected by the stochastic, spatially intermittent intergalactic magnetic field. Here we report measurements of energetic charged-particle propagation through a laser-produced magnetized plasma with these properties. We characterize the diffusive transport of the particles experimentally. The results show that the transport is diffusive and that, for the regime of interest for the highest-energy cosmic rays, the diffusion coefficient is unaffected by the spatial intermittency of the magnetic field.


Measuring the oscillator strength of intercombination lines of helium-like V ions in a laser-produced-plasma

Journal of Quantitative Spectroscopy and Radiative Transfer Elsevier BV (2020) 107326

G Pérez-Callejo, L Jarrott, D Liedahl, M Schneider, J Wark, S Rose


Electron acceleration in laboratory-produced turbulent collisionless shocks

Nature Physics Springer Nature (2020)

GF Swadling, A Grassi, HG Rinderknecht, DP Higginson, DD Ryutov, C Bruulsema, RP Drake, S Funk, S Glenzer, G Gregori, CK Li, BB Pollock, BA Remington, JS Ross, W Rozmus, Y Sakawa, A Spitkovsky, S Wilks, H-S Park

Astrophysical collisionless shocks are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar medium, supernova remnant shocks are observed to amplify magnetic fields and accelerate electrons and protons to highly relativistic speeds. In the well-established model of diffusive shock acceleration, relativistic particles are accelerated by repeated shock crossings. However, this requires a separate mechanism that pre-accelerates particles to enable shock crossing. This is known as the ‘injection problem’, which is particularly relevant for electrons, and remains one of the most important puzzles in shock acceleration. In most astrophysical shocks, the details of the shock structure cannot be directly resolved, making it challenging to identify the injection mechanism. Here we report results from laser-driven plasma flow experiments, and related simulations, that probe the formation of turbulent collisionless shocks in conditions relevant to young supernova remnants. We show that electrons can be effectively accelerated in a first-order Fermi process by small-scale turbulence produced within the shock transition to relativistic non-thermal energies, helping overcome the injection problem. Our observations provide new insight into electron injection at shocks and open the way for controlled laboratory studies of the physics underlying cosmic accelerators.


Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum.

Physical review letters 124 (2020) ARTN 225002

S Vinko, V Vozda, J Andreasson, S Bajt, J Bielecki, T Burian, J Chalupsky, O Ciricosta, M Desjarlais, H Fleckenstein, J Hajdu, V Hajkova, P Hollebon, L Juha, M Kasim, E McBride, K Muehlig, T Preston, D Rackstraw, S Roling, S Toleikis, J Wark, H Zacharias

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.


Calculating Opacity in Hot, Dense Matter Using Second-Order Electron-Photon and Two-Photon Transitions to Approximate Line Broadening.

Physical review letters 125 (2020) 145002-

RA Baggott, SJ Rose, SPD Mangles

Calculations of the opacity of hot, dense matter require models for plasma line broadening. However, the most general theories are too complex to calculate directly and some approximation is inevitably required. The most widely used approaches focus on the line center, where a Lorentzian shape is obtained. Here, we demonstrate that in the opposite limit, far from the line center, the opacity can be expressed in terms of second-order transitions, such as electron-photon and two-photon processes. We suggest that this insight could form the basis for a new approach to improve calculations of opacity in hot, dense matter. Preliminary calculations suggest that this approach could yield increased opacity away from absorption lines.


Time-resolved XUV opacity measurements of warm-dense aluminium

Physical Review Letters American Physical Society 124 (2020) 225002

S Vinko, V Vozda, J Andreasson, O Ciricosta, P Hollebon, M Kasim, DS Rackstraw, J Wark

The free-free opacity in plasmas is fundamental to our understanding of energy transport in stellar interiors and for inertial confinement fusion research. However, theoretical predictions in the challenging dense plasma regime are conflicting and there is a dearth of accurate experimental data to allow for direct model validation. Here we present time-resolved transmission measurements in solid-density Al heated by an XUV free-electron laser. We use a novel functional optimization approach to extract the temperature-dependent absorption coefficient directly from an oversampled pool of single-shot measurements, and find a pronounced enhancement of the opacity as the plasma is heated to temperatures of order of the Fermi energy. Plasma heating and opacity enhancement are observed on ultrafast timescales, within the duration of the femtosecond XUV pulse. We attribute further rises in the opacity on ps timescales to melt and the formation of warm dense matter.


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 Royal Society, The (2020)

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


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 Royal Society, The (2020)

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


Corrections to weighted opacities and energy exchange rate in 3-T radiation-hydrodynamics

High Energy Density Physics Elsevier BV 35 (2020) 100734

KW McLean, SJ Rose


Recovery of a high-pressure phase formed under laser-driven compression

Physical Review B American Physical Society 102 (2020) 24101

M Gorman, D McGonegle, S Tracy, S Clarke, C Bolme, A Gleason, S Ali, S Hok, C Greeff, P Heighway, K Hulpach, B Glam, E Galtier, H Lee, J Wark, J Eggert, J Wicks, R Smith

The recovery of metastable structures formed at high pressure has been a long-standing goal in the field of condensed matter physics. While laser-driven compression has been used as a method to generate novel structures at high pressure, to date no high-pressure phases have been quenched to ambient conditions. Here we demonstrate, using in situ x-ray diffraction and recovery methods, the successful quench of a high-pressure phase which was formed under laser-driven shock compression. We show that tailoring the pressure release path from a shock-compressed state to eliminate sample spall, and therefore excess heating, increases the recovery yield of the high-pressure ω phase of zirconium from 0% to 48%. Our results have important implications for the quenchability of novel phases of matter demonstrated to occur at extreme pressures using nanosecond laser-driven compression.


Role of collisionality and radiative cooling in supersonic plasma jet collisions of different materials

Physical Review E American Physical Society 101 (2020) 023205

Collins, Valenzuela, Speliotopoulos, Aybar, Conti, Beg, Tzeferacos, Khiar, G Gregori

Currently there is considerable interest in creating scalable laboratory plasmas to study the mechanisms behind the formation and evolution of astrophysical phenomena such as Herbig-Haro objects and supernova remnants. Laboratory-scaled experiments can provide a well diagnosed and repeatable supplement to direct observations of these extraterrestrial objects if they meet similarity criteria demonstrating that the same physics govern both systems. Here, we present a study on the role of collision and cooling rates on shock formation using colliding jets from opposed conical wire arrays on a compact pulsed-power driver. These diverse conditions were achieved by changing the wire material feeding the jets, since the ion-ion mean free path (λmfp-ii) and radiative cooling rates (Prad) increase with atomic number. Low Z carbon flows produced smooth, temporally stable shocks. Weakly collisional, moderately cooled aluminum flows produced strong shocks that developed signs of thermal condensation instabilities and turbulence. Weakly collisional, strongly cooled copper flows collided to form thin shocks that developed inconsistently and fragmented. Effectively collisionless, strongly cooled tungsten flows interpenetrated, producing long axial density perturbations.


Investigating off-Hugoniot states using multi-layer ring-up targets.

Scientific reports 10 (2020) 13172-

D McGonegle, PG Heighway, M Sliwa, CA Bolme, AJ Comley, LE Dresselhaus-Marais, A Higginbotham, AJ Poole, EE McBride, B Nagler, I Nam, MH Seaberg, BA Remington, RE Rudd, CE Wehrenberg, JS Wark

Laser compression has long been used as a method to study solids at high pressure. This is commonly achieved by sandwiching a sample between two diamond anvils and using a ramped laser pulse to slowly compress the sample, while keeping it cool enough to stay below the melt curve. We demonstrate a different approach, using a multilayer 'ring-up' target whereby laser-ablation pressure compresses Pb up to 150 GPa while keeping it solid, over two times as high in pressure than where it would shock melt on the Hugoniot. We find that the efficiency of this approach compares favourably with the commonly used diamond sandwich technique and could be important for new facilities located at XFELs and synchrotrons which often have higher repetition rate, lower energy lasers which limits the achievable pressures that can be reached.


Hydrodynamic conditions in laser irradiated buried layer experiments

Physics of Plasmas AIP Publishing 27 (2020) 063301-063301

Y Frank, GE Kemp, EV Marley, GP Callejo, ME Foord, MB Schneider, Y Ehrlich, M Fraenkel


X-ray-line coincidence photopumping in a potassium-chlorine mixed plasma

Physical Review A American Physical Society 101 (2020) 53431

LMR Hobbs, D Burridge, MP Hill, DJ Hoarty, CRD Brown, R Charles, G Cooper, SF James, LA Wilson, W Babbage, PW Hatfield, P Beiersdorfer, J Nilsen, H Scott, S Rose

Exploiting the multiple long pulse capability and suite of x-ray diagnostics of the Orion laser, we have set out to explore line coincidence photopuming—the enhancement in population of an atomic level brought on by resonant absorption of x rays from a different emitting ion. Unlike previous work, the two ions are in the same plasma and so the experiment is an x-ray analog of the well-known Bowen resonance fluorescence mechanism that operates in astrophysical situations in the optical region. Our measurements have shown enhanced fluorescence in a chlorine plasma, attributable to line coincident photopumping from co-mixed potassium ions. To detect this relatively low signal-to-noise phenomenon, the data from multiple shots are combined, and the statistical method of bootstrapping is used to assign a confidence value to the measured enhancement, resulting in an estimate of the enhancement of 39 ± 16 18% compared to the null case, where no pumping occurs. The experimental results have been compared to coupled radiation-transport and radiation hydrodynamics simulations using the cretin code together with the nym radiation hydrodynamics model and agreement has been found, with the simulations also predicting modest enhancement.


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 "https://creativecommons.org/licenses/by/4.0/"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.


Demonstration of femtosecond broadband X-rays from laser wakefield acceleration as a source for pump-probe X-ray absorption studies

High Energy Density Physics Elsevier BV 35 (2020) 100729

K Krushelnick, RA Baggott, TZ Zhao, JM Cole, E Hill, SJ Rose, A Maksimchuk, J Nees, AGR Thomas, SPD Mangles, V Yanovsky, JC Wood, R Watt, AE Hussein, K Behm


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 Royal Society, The (2020)

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


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.


X-ray diffraction at the National Ignition Facility

Review of Scientific Instruments AIP Publishing 91 (2020) 043902

J Rygg, A Lazicki, D Braun, D Fratanduono, J McNaney, D Swift, C Wehrenberg, F Coppari, M Ahmed, M Barrios, K Blobaum, G Collins, P Di Nicola, E Dzenitis, S Gonzales, B Heidl, M Hohenberger, N Izumi, D Kalantar, N Masters, R Vignes, M Wall, J Wark, A Arsenlis, J Eggert

We report details of an experimental platform implemented at the National Ignition Facility to obtain in situ powder diffraction data from solids dynamically compressed to extreme pressures. Thin samples are sandwiched between tamper layers and ramp compressed using a gradual increase in the drive-laser irradiance. Pressure history in the sample is determined using high-precision velocimetry measurements. Up to two independently timed pulses of x rays are produced at or near the time of peak pressure by laser illumination of thin metal foils. The quasi-monochromatic x-ray pulses have a mean wavelength selectable between 0.6 Å and 1.9 Å depending on the foil material. The diffracted signal is recorded on image plates with a typical 2θ x-ray scattering angle uncertainty of about 0.2° and resolution of about 1°. Analytic expressions are reported for systematic corrections to 2θ due to finite pinhole size and sample offset. A new variant of a nonlinear background subtraction algorithm is described, which has been used to observe diffraction lines at signal-to-background ratios as low as a few percent. Variations in system response over the detector area are compensated in order to obtain accurate line intensities; this system response calculation includes a new analytic approximation for image-plate sensitivity as a function of photon energy and incident angle. This experimental platform has been used up to 2 TPa (20 Mbar) to determine the crystal structure, measure the density, and evaluate the strain-induced texturing of a variety of compressed samples spanning periods 2–7 on the periodic table.

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