Publications by Steven Rose

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

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.

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

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

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.

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

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

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.

Laboratory measurements of geometrical effects in the x-ray emission of optically thick lines for ICF diagnostics

Physics of Plasmas AIP Publishing 26 (2019) 063302

G Perez-Callejo, LC Jarrott, DA Liedahl, EV Marley, GE Kemp, RF Heeter, JA Emig, ME Foord, K Widmann, J Jaquez, H Huang, SJ Rose, J Wark, MB Schneider

Understanding the effects of radiative transfer in High Energy Density Physics experiments is critical for the characterization of the thermodynamic properties of highly ionized matter, in particular in Inertial Confinement Fusion (ICF). We report on non-Local Thermodynamic Equilibrium experiments on cylindrical targets carried out at the Omega Laser Facility at the Laboratory for Laser Energetics, Rochester NY, which aim to characterize these effects. In these experiments, a 50/50 mixture of iron and vanadium, with a thickness of 2000 Å and a diameter of 250 μm, is contained within a beryllium tamper, with a thickness of 10 μm and a diameter of 1000 μm. Each side of the beryllium tamper is then irradiated using 18 of the 60 Omega beams with an intensity of roughly 3 × 1014 W cm−2 per side, over a duration of 3 ns. Spectroscopic measurements show that a plasma temperature on the order of 2 keV was produced. Imaging data show that the plasma remains cylindrical, with geometrical aspect ratios (quotient between the height and the radius of the cylinder) from 0.4 to 2.0. The temperatures in this experiment were kept sufficiently low (∼1–2 keV) so that the optically thin Li-like satellite emission could be used for temperature diagnosis. This allowed for the characterization of optical-depth-dependent geometric effects in the vanadium line emission. Simulations present good agreement with the data, which allows this study to benchmark these effects in order to take them into account to deduce temperature and density in future ICF experiments, such as those performed at the National Ignition Facility.

Radiation transfer in cylindrical, toroidal and hemi-ellipsoidal plasmas

Journal of Quantitative Spectroscopy and Radiative Transfer Elsevier BV (2019)

G Pérez-Callejo, JS Wark, SJ Rose

The use of geometric effects in diagnosing ion density in ICF-related dot spectroscopy experiments

High Energy Density Physics Elsevier 30 (2019) 45-51

J Wark, G Perez-Callejo, S Rose, M Schneider, D Liedahl

We describe a method to calculate the ion density of High Energy Density (HED) cylindrical plasmas used in Dot Spectroscopy experiments. This method requires only spectroscopic measurements of the Heα region obtained from two views (Face-on and Side-on). We make use of the fact that the geometry of the plasma affects the observed flux of optically thick lines. The ion density can be derived from the aspect ratio (height-to-radius) of the cylinder and the optical depth of the Heα-y line (1s2p 3P1 → 1s 2 1S0). The aspect ratio and the optical depth of the y line are obtained from the spectra using ratios measured from the two directions of emission of the optically thick Heα-w line (1s2p 1P1 → 1s 2 1S0) and the ratio of the optically thick to thin lines. The method can be applied to mid-Z elements at ion densities of 1019 − 1020 cm−3 and temperatures of a the order of keV, which is a relevant regime for Inertial Confinement Fusion (ICF) experiments.

Enhanced fluorescence from x-ray line coincidence pumping of K-pumped Cl and Mg-pumped Ge plasmas

Proceedings of SPIE Society of Photo-optical Instrumentation Engineers 11111 (2019)

J Nilsen, D Burridge, LMR Hobbs, D Hoarty, P Beiersdorfer, GV Brown, N Hell, D Panchenko, MF Gu, AM Saunders, HA Scott, RA London, P Hatfield, MP Hill, R Charles, L Wilson, CRD Brown, S Rose

A proposal to measure iron opacity at conditions close to the solar convective zone-radiative zone boundary

High Energy Density Physics Elsevier BV (2019)

DJ Hoarty, J Morton, M Jeffery, LK Pattison, A Wardlow, SPD Mangles, SJ Rose, C Iglesias, K Opachich, RF Heeter, TS Perry

The blind implosion-maker: Automated inertial confinement fusion experiment design

Physics of Plasmas AIP Publishing 26 (2019) 062706

PW Hatfield, S Rose, R Scott

The design of inertial confinement fusion (ICF) experiments, alongside improving the development of energy density physics theory and experimental methods, is one of the key challenges in the quest for nuclear fusion as a viable energy source [O. A. Hurricane, J. Phys.: Conf. Ser. 717, 012005 (2016)]. Recent challenges in achieving a high-yield implosion at the National Ignition Facility (NIF) have led to new interest in considering a much wider design parameter space than normally studied [J. L. Peterson et al., Phys. Plasmas 24, 032702 (2017)]. Here, we report an algorithmic approach that can produce reasonable ICF designs with minimal assumptions. In particular, we use the genetic algorithm metaheuristic, in which “populations” of implosions are simulated, the design of the capsule is described by a “genome,” natural selection removes poor designs, high quality designs are “mated” with each other based on their yield, and designs undergo “mutations” to introduce new ideas. We show that it takes ∼5 × 104 simulations for the algorithm to find an original NIF design. We also link this method to other parts of the design process and look toward a completely automated ICF experiment design process—changing ICF from an experiment design problem to an algorithm design problem.

Observing thermal Schwinger pair production

Physical Review A American Physical Society (APS) 99 (2019) 052120

O Gould, S Mangles, A Rajantie, S Rose, C Xie

ALICE: A non-LTE plasma atomic physics, kinetics and lineshape package

High Energy Density Physics Elsevier 26 (2018) 56-67

EG Hill, G Pérez-Callejo, S Rose

All three parts of an atomic physics, atomic kinetics and lineshape code, ALICE, are described. Examples of the code being used to model the emissivity and opacity of plasmas are discussed and interesting features of the code which build on the existing corpus of models are shown throughout.

Ultrafast imaging of laser driven shock waves using betatron x-rays from a laser wakefield accelerator

Scientific Reports Nature 8 (2018) 11010

JC Wood, DJ Chapman, K Poder, NC Lopes, M Rutherford, TG White, F Albert, KT Behm, N Booth, JSJ Bryant, PS Foster, S Glenzer, E Hill, K Krushelnick, Z Najmudin, BB Pollock, S Rose, W Schumaker, RHH Scott, M Sherlock, AGR Thomas, Z Zhao, D Eakins, SPD Mangles

Betatron radiation from laser wakefield accelerators is an ultrashort pulsed source of hard, synchrotron-like x-ray radiation. It emanates from a centimetre scale plasma accelerator producing GeV level electron beams. In recent years betatron radiation has been developed as a unique source capable of producing high resolution x-ray images in compact geometries. However, until now, the short pulse nature of this radiation has not been exploited. This report details the first experiment to utilize betatron radiation to image a rapidly evolving phenomenon by using it to radiograph a laser driven shock wave in a silicon target. The spatial resolution of the image is comparable to what has been achieved in similar experiments at conventional synchrotron light sources. The intrinsic temporal resolution of betatron radiation is below 100 fs, indicating that significantly faster processes could be probed in future without compromising spatial resolution. Quantitative measurements of the shock velocity and material density were made from the radiographs recorded during shock compression and were consistent with the established shock response of silicon, as determined with traditional velocimetry approaches. This suggests that future compact betatron imaging beamlines could be useful in the imaging and diagnosis of high-energy-density physics experiments.

Laser-driven strong magnetostatic fields with applications to charged beam transport and magnetized high energy-density physics

Physics of Plasmas AIP Publishing 25 (2018) 056705

JJ Santos, M Bailly-Grandvaux, M Ehret, AV Arefiev, D Batani, FN Beg, A Calisti, S Ferri, R Florido, P Forestier-Colleoni, S Fujioka, MA Gigosos, L Giuffrida, L Gremillet, JJ Honrubia, S Kojima, P Korneev, KFF Law, J-R Marques, A Morace, C Mosse, O Peyrusse, S Rose, M Roth, F Suzuki-Vidal

Powerful laser-plasma processes are explored to generate discharge currents of a few 100 kA in coil targets, yielding magnetostatic fields (B-fields) in excess of 0.5 kT. The quasi-static currents are provided from hot electron ejection from the laser-irradiated surface. According to our model, which describes the evolution of the discharge current, the major control parameter is the laser irradiance Ilasλ 2 las. The space-time evolution of the B-fields is experimentally characterized by high-frequency bandwidth B-dot probes and by protondeflectometry measurements. The magnetic pulses, of ns-scale, are long enough to magnetize secondary targets through resistive diffusion. We applied it in experiments of laser-generated relativistic electron transport through solid dielectric targets, yielding an unprecedented 5-fold enhancement of the energy-density flux at 60 µm depth, compared to unmagnetized transport conditions. These studies pave the ground for magnetized high-energy density physics investigations, related to laser-generated secondary sources of radiation and/or high-energy particles and their transport, to high-gain fusion energy schemes and to laboratory astrophysics.

Production of photoionized plasmas in the laboratory with x-ray line radiation

Physical Review E American Physical Society 97 (2018) 063203

S White, R Irwin, R Warwick, G Gribakin, G Sarri, FP Keenan, D Riley, S Rose, EG Hill, GJ Ferland, B Han, F Wang, G Zhao

In this paper we report the experimental implementation of a theoretically proposed technique for creating a photoionized plasma in the laboratory using x-ray line radiation. Using a Sn laser plasma to irradiate an Ar gas target, the photoionization parameter, ξ = 4πF/Ne, reached values of order 50 erg cm s−1, where F is the radiation flux in erg cm−2 s−1. The significance of this is that this technique allows us to mimic effective spectral radiation temperatures in excess of 1 keV. We show that our plasma starts to be collisionally dominated before the peak of the x-ray drive. However, the technique is extendable to higher-energy laser systems to create plasmas with parameters relevant to benchmarking codes used to model astrophysical objects.

X-ray line coincidence photopumping in a solar flare

Monthly Notices of the Royal Astronomical Society Oxford University Press 474 (2017) 3782-3786

FP Keenan, K Poppenhaeger, M Mathioudakis, S Rose, J Flowerdew, D Hynes, DJ Christian, J Nilsen, WR Johnson

Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence photopumping in astrophysical sources at optical and ultraviolet wavelengths, with the most famous example being Bowen fluorescence (pumping of O III 303.80 Å by He II), but none to our knowledge in X-rays. However, here we report on a scheme where a He-like line of Ne IX at 11.000 Å is photopumped by He-like Na X at 11.003 Å, which predicts significant intensity enhancement in the Ne IX 82.76 Å transition under physical conditions found in solar flare plasmas. A comparison of our theoretical models with published X-ray observations of a solar flare obtained during a rocket flight provides evidence for line enhancement, with the measured degree of enhancement being consistent with that expected from theory, a truly surprising result. Observations of this enhancement during flares on stars other than the Sun would provide a powerful new diagnostic tool for determining the sizes of flare loops in these distant, spatially unresolved, astronomical sources.