Fast electron energy transport in solid density and compressed plasma

NUCLEAR FUSION 54 (2014) ARTN 054004

P Norreys, D Batani, S Baton, FN Beg, R Kodama, PM Nilson, P Patel, F Perez, JJ Santos, RHH Scott, VT Tikhonchuk, M Wei, J Zhang

Alternative ignition schemes in inertial confinement fusion

Nuclear Fusion 54 (2014)

M Tabak, P Norreys, VT Tikhonchuk, KA Tanaka

This paper presents a short overview of a series of review articles describing alternative approaches to ignition of fusion reactions in inertially confined plasmas. © 2014 IAEA, Vienna.

Equilibration dynamics and conductivity of warm dense hydrogen.

Physical review. E, Statistical, nonlinear, and soft matter physics 90 (2014) 013104-

U Zastrau, P Sperling, A Becker, T Bornath, R Bredow, T Döppner, S Dziarzhytski, T Fennel, LB Fletcher, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, M Harmand, V Hilbert, B Holst, T Laarmann, HJ Lee, T Ma, JP Mithen, R Mitzner, CD Murphy, M Nakatsutsumi, P Neumayer, A Przystawik, S Roling, M Schulz, B Siemer, S Skruszewicz, J Tiggesbäumker, S Toleikis, T Tschentscher, T White, M Wöstmann, H Zacharias, R Redmer

We investigate subpicosecond dynamics of warm dense hydrogen at the XUV free-electron laser facility (FLASH) at DESY (Hamburg). Ultrafast impulsive electron heating is initiated by a ≤ 300-fs short x-ray burst of 92-eV photon energy. A second pulse probes the sample via x-ray scattering at jitter-free variable time delay. We show that the initial molecular structure dissociates within (0.9 ± 0.2) ps, allowing us to infer the energy transfer rate between electrons and ions. We evaluate Saha and Thomas-Fermi ionization models in radiation hydrodynamics simulations, predicting plasma parameters that are subsequently used to calculate the static structure factor. A conductivity model for partially ionized plasma is validated by two-temperature density-functional theory coupled to molecular dynamic simulations and agrees with the experimental data. Our results provide important insights and the needed experimental data on transport properties of dense plasmas.

Exploring Mbar shock conditions and isochorically heated aluminum at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (invited).

The Review of scientific instruments 85 (2014) 11E702-

LB Fletcher, HJ Lee, B Barbrel, M Gauthier, E Galtier, B Nagler, T Döppner, S LePape, T Ma, A Pak, D Turnbull, T White, G Gregori, M Wei, RW Falcone, P Heimann, U Zastrau, JB Hastings, SH Glenzer

Recent experiments performed at the Matter in Extreme Conditions end station of the Linac Coherent Light Source (LCLS) have demonstrated the first spectrally resolved measurements of plasmons from isochorically heated aluminum. The experiments have been performed using a seeded 8-keV x-ray laser beam as a pump and probe to both volumetrically heat and scatter x-rays from aluminum. Collective x-ray Thomson scattering spectra show a well-resolved plasmon feature that is down-shifted in energy by 19 eV. In addition, Mbar shock pressures from laser-compressed aluminum foils using velocity interferometer system for any reflector have been measured. The combination of experiments fully demonstrates the possibility to perform warm dense matter studies at the LCLS with unprecedented accuracy and precision.

Intensity enhancement of O VI ultraviolet emission lines in solar spectra due to opacity

Astrophysical Journal Letters 784 (2014)

FP Keenan, JG Doyle, MS Madjarska, SJ Rose, LA Bowler, J Britton, L McCrink, M Mathioudakis

Opacity is a property of many plasmas. It is normally expected that if an emission line in a plasma becomes optically thick, then its intensity ratio to that of another transition that remains optically thin should decrease. However, radiative transfer calculations undertaken both by ourselves and others predict that under certain conditions the intensity ratio of an optically thick to an optically thin line can show an increase over the optically thin value, indicating an enhancement in the former. These conditions include the geometry of the emitting plasma and its orientation to the observer. A similar effect can take place between lines of differing optical depths. While previous observational studies have focused on stellar point sources, here we investigate the spatially resolved solar atmosphere using measurements of the I(1032 Å)/I(1038 Å) intensity ratio of O VI in several regions obtained with the Solar Ultraviolet Measurements of Emitted Radiation instrument on board the Solar and Heliospheric Observatory satellite. We find several I(1032 Å)/I(1038 Å) ratios observed on the disk to be significantly larger than the optically thin value of 2.0, providing the first detection (to our knowledge) of intensity enhancement in the ratio arising from opacity effects in the solar atmosphere. The agreement between observation and theory is excellent and confirms that the O VI emission originates from a slab-like geometry in the solar atmosphere, rather than from cylindrical structures. © 2014. The American Astronomical Society. All rights reserved.

Imaging Lattice dynamics in individual nanocrystals

Optics InfoBase Conference Papers (2014)

JN Clark, L Beitra, G Xiong, A Higginbotham, DM Fritz, HT Lemke, D Zhu, M Chollet, GJ Williams, M Messerschmidt, B Abbey, RJ Harder, AM Korsunsky, JS Wark, IK Robinson

We report imaging of coherent acoustic phonons on the picosecond time scale within a single nanocrystal using an X-ray free-electron laser. Our results allow unprecedented comparison with predictive models and observation of the vibrational modes. © 2014 OSA.

Equilibration dynamics and conductivity of warm dense hydrogen

PHYSICAL REVIEW E 90 (2014) ARTN 013104

U Zastrau, P Sperling, A Becker, T Bornath, R Bredow, T Doeppner, S Dziarzhytski, T Fennel, LB Fletcher, E Forster, C Fortmann, SH Glenzer, S Goede, G Gregori, M Harmand, V Hilbert, B Holst, T Laarmann, HJ Lee, T Ma, JP Mithen, R Mitzner, CD Murphy, M Nakatsutsumi, P Neumayer, A Przystawik, S Roling, M Schulz, B Siemer, S Skruszewicz, J Tiggesbaeumker, S Toleikis, T Tschentscher, T White, M Woestmann, H Zacharias, R Redmer

A photon-photon collider in a vacuum hohlraum

Nature Photonics 8 (2014) 434-436

OJ Pike, F MacKenroth, EG Hill, SJ Rose

The ability to create matter from light is amongst the most striking predictions of quantum electrodynamics. Experimental signatures of this have been reported in the scattering of ultra-relativistic electron beams with laser beams, intense laser-plasma interactions and laser-driven solid target scattering. However, all such routes involve massive particles. The simplest mechanism by which pure light can be transformed into matter, Breit-Wheeler pair production (' 3' 3' €2 ' †' e + e ∼'), has never been observed in the laboratory. Here, we present the design of a new class of photon-photon collider in which a gamma-ray beam is fired into the high-temperature radiation field of a laser-heated hohlraum. Matching experimental parameters to current-generation facilities, Monte Carlo simulations suggest that this scheme is capable of producing of the order of 10 5 Breit-Wheeler pairs in a single shot. This would provide the first realization of a pure photon-photon collider, representing the advent of a new type of high-energy physics experiment. © 2014 Macmillan Publishers Limited.

Dynamical friction in a relativistic plasma

Physical Review E 89 (2014)

OJ Pike, SJ Rose

Comley et al. reply.

Physical review letters 113 (2014) 039602-

AJ Comley, BR Maddox, RE Rudd, NR Barton, CE Wehrenberg, ST Prisbrey, JA Hawreliak, DA Orlikowski, SC Peterson, JH Satcher, AJ Elsholz, H-S Park, BA Remington, N Bazin, JM Foster, P Graham, N Park, PA Rosen, SD Rothman, A Higginbotham, M Suggit, JS Wark

Present status of fast ignition realization experiment and inertial fusion energy development

Nuclear Fusion 53 (2013)

H Azechi, K Mima, S Shiraga, S Fujioka, H Nagatomo, T Johzaki, T Jitsuno, M Key, R Kodama, M Koga, K Kondo, J Kawanaka, N Miyanaga, M Murakami, K Nagai, M Nakai, H Nakamura, T Nakamura, T Nakazato, Y Nakao, K Nishihara, H Nishimura, T Norimatsu, P Norreys, T Ozaki, J Pasley, H Sakagami, Y Sakawa, N Sarukura, K Shigemori, T Shimizu, A Sunahara, T Taguchi, K Tanaka, K Tsubakimoto, Y Fujimoto, H Homma, A Iwamoto

One of the most advanced fast ignition programmes is the fast ignition realization experiment (FIREX). The goal of its first phase is to demonstrate ignition temperature of 5 keV, followed by the second phase to demonstrate ignition-and-burn. The second series experiment of FIREX-I, from late 2010 to early 2011, has demonstrated a high ( > 10%) coupling efficiency from laser to thermal energy of the compressed core, suggesting that the ignition temperature can be achieved at laser energy below 10 kJ. Further improvement of the coupling efficiency is expected by introducing laser-driven magnetic fields. © 2013 IAEA, Vienna.

High Mach-number collisionless shock driven by a laser with an external magnetic field

EPJ Web of Conferences 59 (2013)

T Morita, Y Sakawa, Y Kuramitsu, T Ide, K Nishio, M Kuwada, H Ide, K Tsubouchi, H Yoneda, A Nishida, T Namiki, T Norimatsu, K Tomita, K Nakayama, K Inoue, K Uchino, M Nakatsutsumi, A Pelka, M Koenig, Q Dong, D Yuan, G Gregori, H Takabe

Collisionless shocks are produced in counter-streaming plasmas with an external magnetic field. The shocks are generated due to an electrostatic field generated in counter-streaming laser-irradiated plasmas, as reported previously in a series of experiments without an external magnetic field [T. Morita et al., Phys. Plasmas, 17, 122702 (2010), Kuramitsu et al., Phys. Rev. Lett., 106, 175002 (2011)] via laser-irradiation of a double-CH-foil target. A magnetic field is applied to the region between two foils by putting an electro-magnet (∼10 T) perpendicular to the direction of plasma expansion. The generated shocks show different characteristics later in time (t > 20ns). © Owned by the authors, published by EDP Sciences, 2013.

High-power laser experiments to study collisionless shock generation

EPJ Web of Conferences 59 (2013)

Y Sakawa, Y Kuramitsu, T Morita, T Kato, H Tanji, T Ide, K Nishio, M Kuwada, T Tsubouchi, H Ide, T Norimatsu, C Gregory, N Woolsey, K Schaar, C Murphy, G Gregori, A Diziere, A Pelka, M Koenig, S Wang, Q Dong, Y Li, HS Park, S Ross, N Kugland, D Ryutov, B Remington, A Spitkovsky, D Froula, H Takabe

A collisionless Weibel-instability mediated shock in a self-generated magnetic field is studied using two-dimensional particle-in-cell simulation [Kato and Takabe, Astophys. J. Lett. 681, L93 (2008)]. It is predicted that the generation of the Weibel shock requires to use NIF-class high-power laser system. Collisionless electrostatic shocks are produced in counter-streaming plasmas using Gekko XII laser system [Kuramitsu et al., Phys. Rev. Lett. 106, 175002 (2011)] . A NIF facility time proposal is approved to study the formation of the collisionless Weibel shock. OMEGA and OMEGA EP experiments have been started to study the plasma conditions of counter-streaming plasmas required for the NIF experiment using Thomson scattering and to develop proton radiography diagnostics. © Owned by the authors, published by EDP Sciences, 2013.

Ultrafast three-dimensional imaging of lattice dynamics in individual gold nanocrystals.

Science 341 (2013) 56-59

JN Clark, L Beitra, G Xiong, A Higginbotham, DM Fritz, HT Lemke, D Zhu, M Chollet, GJ Williams, M Messerschmidt, B Abbey, RJ Harder, AM Korsunsky, JS Wark, IK Robinson

Key insights into the behavior of materials can be gained by observing their structure as they undergo lattice distortion. Laser pulses on the femtosecond time scale can be used to induce disorder in a "pump-probe" experiment with the ensuing transients being probed stroboscopically with femtosecond pulses of visible light, x-rays, or electrons. Here we report three-dimensional imaging of the generation and subsequent evolution of coherent acoustic phonons on the picosecond time scale within a single gold nanocrystal by means of an x-ray free-electron laser, providing insights into the physics of this phenomenon. Our results allow comparison and confirmation of predictive models based on continuum elasticity theory and molecular dynamics simulations.

Molecular dynamics simulations of shock-induced deformation twinning of a body-centered-cubic metal

PHYSICAL REVIEW B 88 (2013) ARTN 104105

A Higginbotham, MJ Suggit, EM Bringa, P Erhart, JA Hawreliak, G Mogni, N Park, BA Remington, JS Wark

Measuring fast electron spectra and laser absorption in relativistic laser-solid interactions using differential bremsstrahlung photon detectors.

Rev Sci Instrum 84 (2013) 083505-

RHH Scott, EL Clark, F Pérez, MJV Streeter, JR Davies, H-P Schlenvoigt, JJ Santos, S Hulin, KL Lancaster, SD Baton, SJ Rose, PA Norreys

A photon detector suitable for the measurement of bremsstrahlung spectra generated in relativistically intense laser-solid interactions is described. The Monte Carlo techniques used to extract the fast electron spectrum and laser energy absorbed into forward-going fast electrons are detailed. A relativistically intense laser-solid experiment using frequency doubled laser light is used to demonstrate the effective operation of the detector. The experimental data were interpreted using the 3-spatial-dimension Monte Carlo code MCNPX [D. Pelowitz, MCNPX User's Manual Version 2.6.0, Los Alamos National Laboratory, 2008], and the fast electron temperature found to be 125 keV.

FLASH hydrodynamic simulations of experiments to explore the generation of cosmological magnetic fields

High Energy Density Physics 9 (2013) 75-81

A Scopatz, M Fatenejad, N Flocke, G Gregori, M Koenig, DQ Lamb, D Lee, J Meinecke, A Ravasio, P Tzeferacos, K Weide, R Yurchak

We report the results of FLASH hydrodynamic simulations of the experiments conducted by the University of Oxford High Energy Density Laboratory Astrophysics group and its collaborators at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI). In these experiments, a long-pulse laser illuminates a target in a chamber filled with Argon gas, producing shock waves that generate magnetic fields via the Biermann battery mechanism. The simulations show that the result of the laser illuminating the target is a series of complex hydrodynamic phenomena. © 2012 Elsevier B.V.

Electron–positron pair creation in burning thermonuclear plasmas

High Energy Density Physics 9 (2013) 480-483

SJ Rose

Kinetic simulations of the heating of solid density plasma by femtosecond laser pulses

High Energy Density Physics 9 (2013) 38-41

M Sherlock, EG Hill, SJ Rose

Fourier-transform inelastic X-ray scattering from time- and momentum-dependent phonon-phonon correlations

Nature Physics (2013)

M Trigo, M Fuchs, J Chen, MP Jiang, AM Lindenberg, DA Reis, K Gaffney, S Ghimire, ME Kozina, G Ndabashimiye, M Cammarata, DM Fritz, H Lemke, D Zhu, S Fahy, A Higginbotham, JS Wark, SL Johnson, J Larsson, F Quirin, K Sokolowski-Tinten, C Uher, G Wang

The macroscopic characteristics of a material are determined by its elementary excitations, which dictate the response of the system to external stimuli. The spectrum of excitations is related to fluctuations in the density-density correlations and is typically measured through frequency-domain neutron or X-ray scattering. Time-domain measurements of these correlations could yield a more direct way to investigate the excitations of solids and their couplings both near to and far from equilibrium. Here we show that we can access large portions of the phonon dispersion of germanium by measuring the diffuse scattering from femtosecond X-ray free-electron laser pulses. A femtosecond optical laser pulse slightly quenches the vibrational frequencies, producing pairs of high-wavevector phonons with opposite momenta. These phonons manifest themselves as time-dependent coherences in the displacement correlations probed by the X-ray scattering. As the coherences are preferentially created in regions of strong electron-phonon coupling, the time-resolved approach is a natural spectroscopic tool for probing low-energy collective excitations in solids, and their microscopic interactions.