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.

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.

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

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.

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.

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.

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.

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

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

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.

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.

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

L Fletcher, H Lee, T Doppner, E Galtier, B Nagler, P Heimann, C Fortmann, S LePape, T Ma, M Millot, A Pak, D Turnbull, D Chapman, D Gericke, J Vorberger, G Gregori, B Barbrel, R Falcone, C-C Kao, H Nuhn, J Welch, U Zastrau, P Neumayer, J Hastings, S Glenzer

Free Electron Relativistic Correction Factors to Collisional Excitation and Ionisation Rates in a Plasma

High Energy Density Physics Elsevier BV (2019) 100716

JJ Beesley, SJ Rose

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.

Ultrafast laser-matter interaction with nanostructured targets


RS Marjoribanks, L Lecherbourg, J Sipe, G Kulcsar, A Heron, J-C Adam, A Miscampbell, G Thomas, R Royle, O Humphries, R Ko, S Le Moal, A Tan, J Li, T Preston, Q van den Berg, M Kasim, B Nagler, E Galtier, E Cunningham, J Wark, S Vinko

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.

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.

Observation of He-like satellite lines of the H-like potassium K XIX emission

Astrophysical Journal American Astronomical Society 881 (2019) 92

ME Weller, P Beiersdorfer, TE Lockard, GV Brown, A McKelvey, J Nilsen, R Shepherd, VA Soukhanovskii, MP Hill, LMR Hobbs, D Burridge, DJ Hoarty, J Morton, L Wilson, S Rose, P Hatfield

We present measurements of the H-like potassium (K xix) X-ray spectrum and its He-like (K xviii) satellite lines, which are situated in the wavelength region between 3.34 and 3.39 Å, which has been of interest for the detection of dark matter. The measurements were taken with a high-resolution X-ray spectrometer from targets irradiated by a long-pulse (2 ns) beam from the Orion laser facility. We obtain experimental wavelength values of dielectronic recombination satellite lines and show that the ratio of the Lyα lines and their dielectronic satellite lines can be used to estimate the electron temperature, which in our case was about 1.5 ± 0.3 keV.

Molecular dynamics simulations of grain interactions in shock-compressed highly textured columnar nanocrystals

Physical Review Materials American Physical Society 3 (2019) 083602

P Heighway, F McGonegle, N Park, A Higginbotham, J Wark

While experimental and computational studies abound demonstrating the diverse range of phenomena caused by grain interactions under quasistatic loading conditions, far less attention has been given to these interactions under the comparatively dramatic conditions of shock compression. The consideration of grain interactions is essential within the context of contemporary shock-compression experiments that exploit the distinctive x-ray diffraction patterns of highly textured (and therefore strongly anisotropic) targets in order to interrogate local structural evolution. We present here a study of grain interaction effects in shock-compressed, body-centered cubic tantalum nanocrystals characterized by a columnar geometry and a strong fiber texture using large-scale molecular dynamics simulations. Our study reveals that contiguous grains deform cooperatively in directions perpendicular to the shock, driven by the gigapascal-scale stress gradients induced over their boundaries by the uniaxial compression, and in so doing are able to reach a state of reduced transverse shear stress. We compare the extent of this relaxation for two different columnar geometries (distinguished by their square or hexagonal cross-sections), and quantify the attendant change in the transverse elastic strains. We further show that cooperative deformation is able to replace ordinary plastic deformation mechanisms at lower shock pressures, and, under certain conditions, activate new mechanisms at higher pressures.