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

Time-Resolved XUV Opacity Measurements of Warm Dense Aluminum.

Physical review letters 124 (2020) 225002-

SM Vinko, V Vozda, J Andreasson, S Bajt, J Bielecki, T Burian, J Chalupsky, O Ciricosta, MP Desjarlais, H Fleckenstein, J Hajdu, V Hajkova, P Hollebon, L Juha, MF Kasim, EE McBride, K Muehlig, TR Preston, DS Rackstraw, S Roling, S Toleikis, JS 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.

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

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.

Using sparse Gaussian processes for predicting robust inertial confinement fusion implosion yields

IEEE Transactions on Plasma Science IEEE (2019) 1-6

P Hatfield, S Rose, R Scott, I Almosallam, S Roberts, M Jarvis

Laser produced electromagnetic pulses: generation, detection and mitigation


F Consoli, VT Tikhonchuk, M Bardon, P Bradford, DC Carroll, J Cikhardt, M Cipriani, RJ Clarke, TE Cowan, CN Danson, R De Angelis, M De Marco, J-L Dubois, B Etchessahar, AL Garcia, DI Hillier, A Honsa, W Jiang, V Kmetik, J Krasa, Y Li, F Lubrano, P McKenna, J Metzkes-Ng, A Poye, I Prencipe, P Raczka, RA Smith, R Vrana, NC Woolsey, E Zemaityte, Y Zhang, Z Zhang, B Zielbauer, D Neely

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

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

Up to two billion times acceleration of scientific simulations with deep neural architecture search

CoRR abs/2001.08055 (2020)

MF Kasim, D Watson-Parris, L Deaconu, S Oliver, P Hatfield, DH Froula, G Gregori, M Jarvis, S Khatiwala, J Korenaga, J Topp-Mugglestone, E Viezzer, SM Vinko

Computer simulations are invaluable tools for scientific discovery. However, accurate simulations are often slow to execute, which limits their applicability to extensive parameter exploration, large-scale data analysis, and uncertainty quantification. A promising route to accelerate simulations by building fast emulators with machine learning requires large training datasets, which can be prohibitively expensive to obtain with slow simulations. Here we present a method based on neural architecture search to build accurate emulators even with a limited number of training data. The method successfully accelerates simulations by up to 2 billion times in 10 scientific cases including astrophysics, climate science, biogeochemistry, high energy density physics, fusion energy, and seismology, using the same super-architecture, algorithm, and hyperparameters. Our approach also inherently provides emulator uncertainty estimation, adding further confidence in their use. We anticipate this work will accelerate research involving expensive simulations, allow more extensive parameters exploration, and enable new, previously unfeasible computational discovery.

Experimental characterization of the interaction zone between counter propagating Taylor Sedov blast waves

Physics of Plasmas AIP Publishing 27 (2020) 022111

B Albertazzi, P Mabey, T Michel, G Rigon, Marques, S Pikuz, S Ryazantsev, E Falize, L Van Box Som, J Meinecke, N Ozaki, A Ciardi, G Gregori, M Koenig

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jets winds etc.) is a common process which leads to a more intricate structure of the Interstellar medium (ISM). In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNR) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage and the distance between the two stars. In this letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BW) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼ 500 J) of 300 µm diameter carbon rods and propagate in different gases (Ar and N) at different pressures. The physical parameters, such as density and temperature of the IR are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17-20 % increase of temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long times after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect.

X-ray diffraction at the National Ignition Facility

Review of Scientific Instruments AIP Publishing 91 (2020) 043902-043902

D Braun, D Fratanduono, R Kraus, J McNaney, D Swift, C Wehrenberg, F Coppari, M Ahmed, M Barrios, K Blobaum, G Collins, A Cook, P Di Nicola, E Dzenitis, S Gonzales, B Heidl, M Hohenberger, R Vignes, M Wall, J Ward, J Wark, T Zobrist, A Arsenlis, J Eggert

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.

Reply to: Reconsidering X-ray plasmons

NATURE PHOTONICS 13 (2019) 751-753

LB Fletcher, HJ Lee, T Doppner, E Galtier, B Nagler, P Heimann, C Fortmann, S LePape, T Ma, M Millot, A Pak, D Turnbull, DA Chapman, DO Gericke, J Vorberger, T White, G Gregori, M Wei, B Barbrel, RW Falcone, C-C Kao, H Nuhn, J Welch, U Zastrau, P Neumayer, JB Hastings, SH Glenzer

Non-isentropic release of a shocked solid

Physical Review Letters American Physical Society 123 (2019) 245501

PG Heighway, M Sliwa, D McGonegle, C Wehrenberg, CA Bolme, J Eggert, A Higginbotham, A Lazicki, HJ Lee, B Nagler, H-S Park, RE Rudd, RF Smith, MJ Suggit, D Swift, F Tavella, BA Remington, J Wark

We present molecular dynamics simulations of shock and release in micron-scale tantalum crystals that exhibit postbreakout temperatures far exceeding those expected under the standard assumption of isentropic release. We show via an energy-budget analysis that this is due to plastic-work heating from material strength that largely counters thermoelastic cooling. The simulations are corroborated by experiments where the release temperatures of laser-shocked tantalum foils are deduced from their thermal strains via in situ x-ray diffraction and are found to be close to those behind the shock.

Coordination changes in liquid tin under shock compression determined using in situ femtosecond x-ray diffraction

Applied Physics Letters AIP Publishing 115 (2019) 264101

R Briggs, S Zhang, D McGonegle, AL Coleman, F Coppari, MA Morales-Silva, RF Smith, JK Wicks, CA Bolme, AE Gleason, E Cunningham, HJ Lee, B Nagler, MI McMahon, JH Eggert, DE Fratanduono

Little is known regarding the liquid structure of materials compressed to extreme conditions, and even less is known about liquid structures undergoing rapid compression on nanosecond timescales. Here, we report on liquid structure factor and radial distribution function measurements of tin shock compressed to 84(19) GPa. High-quality, femtosecond x-ray diffraction measurements at the Linac Coherent Light Source were used to extract the liquid diffuse scattering signal. From the radial distribution function, we find that the structural evolution of the liquid with increasing pressure mimics the evolution of the solid phase. With increasing pressure, we find that the liquid structure evolves from a complex structure, with a low coordination number, to a simple liquid structure with a coordination number of 12. We provide a pathway for future experiments to study liquids at elevated pressures using high-energy lasers to shock compress materials beyond the reach of static diamond anvil cell techniques.

Kinetic simulations of fusion ignition with hot-spot ablator mix

Physical Review E American Physical Society 100 (2019) 033206

J Sadler, Y Lu, B Spiers, M Mayr, A Savin, R Wang, R Aboushelbaya, K Glize, R Bingham, H Li, K Flippo, P Norreys

Inertial confinement fusion fuel suffers increased X-ray radiation losses when carbon from the capsule ablator mixes into the hot-spot. Here we present one and two-dimensional ion VlasovFokker-Planck simulations that resolve hot-spot self heating in the presence a localised spike of carbon mix, totalling 1.9 % of the hot-spot mass. The mix region cools and contracts over tens of picoseconds, increasing its alpha particle stopping power and radiative losses. This makes a localised mix region more severe than an equal amount of uniformly distributed mix. There is also a purely kinetic effect that reduces fusion reactivity by several percent, since faster ions in the tail of the distribution are absorbed by the mix region. Radiative cooling and contraction of the spike induces fluid motion, causing neutron spectrum broadening. This artificially increases the inferred experimental ion temperatures and gives line of sight variations.

Inverse problem instabilities in large-scale modelling of matter in extreme conditions

Physics of Plasmas AIP Publishing 26 (2019) 112706

MF Kasim, TP Galligan, J Topp-Mugglestone, G Gregori, S Vinko

Our understanding of physical systems often depends on our ability to match complex computational modeling with the measured experimental outcomes. However, simulations with large parameter spaces suffer from inverse problem instabilities, where similar simulated outputs can map back to very different sets of input parameters. While of fundamental importance, such instabilities are seldom resolved due to the intractably large number of simulations required to comprehensively explore parameter space. Here, we show how Bayesian inference can be used to address inverse problem instabilities in the interpretation of x-ray emission spectroscopy and inelastic x-ray scattering diagnostics. We find that the extraction of information from measurements on the basis of agreement with simulations alone is unreliable and leads to a significant underestimation of uncertainties. We describe how to statistically quantify the effect of unstable inverse models and describe an approach to experimental design that mitigates its impact.

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.

Ab initio simulations and measurements of the free-free opacity in aluminum

Physical Review E American Physical Society 100 (2019) 043207

P Hollebon, O Ciricosta, MP Desjarlais, C Cacho, C Spindloe, E Springate, ICE Turcu, J Wark, SM Vinko

The free-free opacity in dense systems is a property that both tests our fundamental understanding of correlated many-body systems, and is needed to understand the radiative properties of high energy-density plasmas. Despite its importance, predictive calculations of the free-free opacity remain challenging even in the condensed matter phase for simple metals. Here we show how the free-free opacity can be modelled at finite-temperatures via time-dependent density functional theory, and illustrate the importance of including local field corrections, core polarization, and self-energy corrections. Our calculations for ground-state Al are shown to agree well with experimental opacity measurements performed on the Artemis laser facility across a wide range of extreme ultraviolet wavelengths. We extend our calculations across the melt to the warm-dense matter regime, finding good agreement with advanced plasma models based on inverse bremsstrahlung at temperatures above 10 eV.

Axion-like-particle decay in strong electromagnetic backgrounds

Journal of High Energy Physics Springer 2019 (2019) 162

B King, BM Dillon, K Beyer, G Gregori