Publications


Magnetic field generation during intense laser channelling in underdense plasma

Physics of Plasmas 23 (2016)

AG Smyth, G Sarri, M Vranic, Y Amano, D Doria, E Guillaume, H Habara, R Heathcote, G Hicks, Z Najmudin, H Nakamura, PA Norreys, S Kar, LO Silva, KA Tanaka, J Vieira, M Borghesi

© 2016 Author(s). Channel formation during the propagation of a high-energy (120 J) and long duration (30 ps) laser pulse through an underdense deuterium plasma has been spatially and temporally resolved via means of a proton imaging technique, with intrinsic resolutions of a few μm and a few ps, respectively. Conclusive proof is provided that strong azimuthally symmetric magnetic fields with a strength of around 0.5 MG are created inside the channel, consistent with the generation of a collimated beam of relativistic electrons. The inferred electron beam characteristics may have implications for the cone-free fast-ignition scheme of inertial confinement fusion.


Simulations of the time and space-resolved x-ray transmission of a free-electron-laser-heated aluminium plasma

JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 49 (2016) ARTN 035603

DS Rackstraw, SM Vinko, O Ciricosta, H-K Chung, RW Lee, JS Wark


Relativistic intensity laser interactions with low-density plasmas

Journal of Physics: Conference Series IOP Publishing 688 (2016) 012126-012126

L Willingale, PM Nilson, C Zulick, H Chen, RS Craxton, J Cobble, A Maksimchuk, P Norreys, TC Sangster, RHH Scott, C Stoeckl

© Published under licence by IOP Publishing Ltd. We perform relativistic-intensity laser experiments using the Omega EP laser to investigate channeling phenomena and particle acceleration in underdense plasmas. A fundamental understanding of these processes is of importance to the hole-boring fast ignition scheme for inertial confinement fusion. Proton probing was used to image the electromagnetic fields formed as the Omega EP laser pulse generated a channel through underdense plasma. Filamentation of the channel was observed, followed by self-correction into a single channel. The channel radius as a function of time was found to be in reasonable agreement with momentum- conserving snowplough models.


A laboratory model of post-Newtonian gravity with high power lasers and 4th generation light sources

CLASSICAL AND QUANTUM GRAVITY 33 (2016) ARTN 075010

G Gregori, MC Levy, MA Wadud, BJB Crowley, R Bingham


Inelastic response of silicon to shock compression.

Scientific reports 6 (2016) 24211-

A Higginbotham, PG Stubley, AJ Comley, JH Eggert, JM Foster, DH Kalantar, D McGonegle, S Patel, LJ Peacock, SD Rothman, RF Smith, MJ Suggit, JS Wark

The elastic and inelastic response of [001] oriented silicon to laser compression has been a topic of considerable discussion for well over a decade, yet there has been little progress in understanding the basic behaviour of this apparently simple material. We present experimental x-ray diffraction data showing complex elastic strain profiles in laser compressed samples on nanosecond timescales. We also present molecular dynamics and elasticity code modelling which suggests that a pressure induced phase transition is the cause of the previously reported 'anomalous' elastic waves. Moreover, this interpretation allows for measurement of the kinetic timescales for transition. This model is also discussed in the wider context of reported deformation of silicon to rapid compression in the literature.


Laboratory analogue of a supersonic accretion column in a binary star system.

Nature communications 7 (2016) ncomms11899-

JE Cross, G Gregori, JM Foster, P Graham, J-M Bonnet-Bidaud, C Busschaert, N Charpentier, CN Danson, HW Doyle, RP Drake, J Fyrth, ET Gumbrell, M Koenig, C Krauland, CC Kuranz, B Loupias, C Michaut, M Mouchet, S Patankar, J Skidmore, C Spindloe, ER Tubman, N Woolsey, R Yurchak, É Falize

Astrophysical flows exhibit rich behaviour resulting from the interplay of different forms of energy-gravitational, thermal, magnetic and radiative. For magnetic cataclysmic variable stars, material from a late, main sequence star is pulled onto a highly magnetized (B>10 MG) white dwarf. The magnetic field is sufficiently large to direct the flow as an accretion column onto the poles of the white dwarf, a star subclass known as AM Herculis. A stationary radiative shock is expected to form 100-1,000 km above the surface of the white dwarf, far too small to be resolved with current telescopes. Here we report the results of a laboratory experiment showing the evolution of a reverse shock when both ionization and radiative losses are important. We find that the stand-off position of the shock agrees with radiation hydrodynamic simulations and is consistent, when scaled to AM Herculis star systems, with theoretical predictions.


Numerical study of neutron beam divergence in a beam-fusion scenario employing laser driven ions

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 829 (2016) 176-180

A Alejo, A Green, H Ahmed, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, P McKenna, SR Mirfayzi, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi, S Kar


Efficient evaluation of collisional energy transfer terms for plasma particle simulations

JOURNAL OF PLASMA PHYSICS 82 (2016) ARTN 905820107

AE Turrell, M Sherlock, SJ Rose


Model experiment of magnetic field amplification in laser-produced plasmas via the Richtmyer-Meshkov instability

PHYSICS OF PLASMAS 23 (2016) ARTN 032126

Y Kuramitsu, N Ohnishi, Y Sakawa, T Morita, H Tanji, T Ide, K Nishio, CD Gregory, JN Waugh, N Booth, R Heathcote, C Murphy, G Gregori, J Smallcombe, C Barton, A Diziere, M Koenig, N Woolsey, Y Matsumoto, A Mizuta, T Sugiyama, S Matsukiyo, T Moritaka, T Sano, H Takabe


Nanosecond formation of diamond and lonsdaleite by shock compression of graphite.

Nature communications 7 (2016) 10970-

D Kraus, A Ravasio, M Gauthier, DO Gericke, J Vorberger, S Frydrych, J Helfrich, LB Fletcher, G Schaumann, B Nagler, B Barbrel, B Bachmann, EJ Gamboa, S Göde, E Granados, G Gregori, HJ Lee, P Neumayer, W Schumaker, T Döppner, RW Falcone, SH Glenzer, M Roth

The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedented in situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.


Mitigating the hosing instability in relativistic laser-plasma interactions

NEW JOURNAL OF PHYSICS 18 (2016) ARTN 053023

L Ceurvorst, N Ratan, MC Levy, MF Kasim, J Sadler, RHH Scott, RMGM Trines, TW Huang, M Skramic, M Vranic, LO Silva, PA Norreys


Characteristics of betatron radiation from direct-laser-accelerated electrons.

Physical review. E 93 (2016) 063203-

TW Huang, APL Robinson, CT Zhou, B Qiao, B Liu, SC Ruan, XT He, PA Norreys

Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S(≡n_{e}/n_{c}a_{0}). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a_{0}) for a fixed value of S. As a result, the total number of radiated photons scales as a_{0}^{2}/sqrt[S] and the energy conversion efficiency of photons from the accelerated electrons scales as a_{0}^{3}/S. The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.


Beamed neutron emission driven by laser accelerated light ions

NEW JOURNAL OF PHYSICS 18 (2016) ARTN 053002

S Kar, A Green, H Ahmed, A Alejo, APL Robinson, M Cerchez, R Clarke, D Doria, S Dorkings, J Fernandez, SR Mirfayzi, P McKenna, K Naughton, D Neely, P Norreys, C Peth, H Powell, JA Ruiz, J Swain, O Willi, M Borghesi


Characteristics of betatron radiation from direct-laser-accelerated electrons

Physical Review E American Physical Society 93 (2016) 063203

APL Robinson, CT Zhou, B Qiao, B Liu, SC Ruan, P Norreys, TW Huang, XT He

<p>Betatron radiation from direct-laser-accelerated electrons is characterized analytically and numerically. It is shown here that the electron dynamics is strongly dependent on a self-similar parameter S ( ≡ n e n c a 0 ). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field ( a 0 )fora fixed value of S . As a result, the total number of radiated photons scales as a 2 0 / √ S and the energy conversion efficiency of photons from the accelerated electrons scales as a 3 0 /S . The particle-in-cell simulations agree well with the analytical scalings. It is suggested that a tunable high-energy and high-flux radiation source can be achieved by exploiting this regime.</p>


Dynamic X-ray diffraction observation of shocked solid iron up to 170 GPa.

Proceedings of the National Academy of Sciences of the United States of America 113 (2016) 7745-7749

A Denoeud, N Ozaki, A Benuzzi-Mounaix, H Uranishi, Y Kondo, R Kodama, E Brambrink, A Ravasio, M Bocoum, J-M Boudenne, M Harmand, F Guyot, S Mazevet, D Riley, M Makita, T Sano, Y Sakawa, Y Inubushi, G Gregori, M Koenig, G Morard

Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.


Experimental measurements of the collisional absorption of XUV radiation in warm dense aluminium.

Physical review. E 94 (2016) 023203-

B Kettle, T Dzelzainis, S White, L Li, B Dromey, M Zepf, CLS Lewis, G Williams, S Künzel, M Fajardo, H Dacasa, P Zeitoun, A Rigby, G Gregori, C Spindloe, R Heathcote, D Riley

The collisional (or free-free) absorption of soft x rays in warm dense aluminium remains an unsolved problem. Competing descriptions of the process exist, two of which we compare to our experimental data here. One of these is based on a weak scattering model, another uses a corrected classical approach. These two models show distinctly different behaviors with temperature. Here we describe experimental evidence for the absorption of 26-eV photons in solid density warm aluminium (T_{e}≈1 eV). Radiative x-ray heating from palladium-coated CH foils was used to create the warm dense aluminium samples and a laser-driven high-harmonic beam from an argon gas jet provided the probe. The results indicate little or no change in absorption upon heating. This behavior is in agreement with the prediction of the corrected classical approach, although there is not agreement in absolute absorption value. Verifying the correct absorption mechanism is decisive in providing a better understanding of the complex behavior of the warm dense state.


Transport coefficients of a relativistic plasma

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics American Physical Society 93 (2016) 1-16

SJ Rose, OJ Pike

In this work, a self-consistent transport theory for a relativistic plasma is developed. Using the notation of Braginskii [S. I. Braginskii, in Reviews of Plasma Physics, ed. M. A. Leontovich (1965), Vol. 1, p.174], we provide semi-analytical forms of the electrical resistivity, thermoelectric and thermal conductivity tensors for a Lorentzian plasma in a magnetic field. This treatment is then generalized to plasmas with arbitrary atomic number by numerically solving the linearized Boltzmann equation. The corresponding transport coefficients are fitted by rational functions in order to make them suitable for use in radiation-hydrodynamic simulations and transport calculations. Within the confines of linear transport theory and on the assumption that the plasma is optically thin, our results are valid for temperatures up to a few MeV. By contrast, classical transport theory begins to incur significant errors above kBT ~ 10 keV, e.g., the parallel thermal conductivity is suppressed by 15% at kBT = 20 keV due to relativistic effects


Theory of Thomson scattering in inhomogeneous media.

Scientific reports 6 (2016) 24283-

PM Kozlowski, BJB Crowley, DO Gericke, SP Regan, G Gregori

Thomson scattering of laser light is one of the most fundamental diagnostics of plasma density, temperature and magnetic fields. It relies on the assumption that the properties in the probed volume are homogeneous and constant during the probing time. On the other hand, laboratory plasmas are seldom uniform and homogeneous on the temporal and spatial dimensions over which data is collected. This is particularly true for laser-produced high-energy-density matter, which often exhibits steep gradients in temperature, density and pressure, on a scale determined by the laser focus. Here, we discuss the modification of the cross section for Thomson scattering in fully-ionized media exhibiting steep spatial inhomogeneities and/or fast temporal fluctuations. We show that the predicted Thomson scattering spectra are greatly altered compared to the uniform case, and may lead to violations of detailed balance. Therefore, careful interpretation of the spectra is necessary for spatially or temporally inhomogeneous systems.


Measurements of continuum lowering in solid-density plasmas created from elements and compounds.

Nature communications 7 (2016) 11713-

O Ciricosta, SM Vinko, B Barbrel, DS Rackstraw, TR Preston, T Burian, J Chalupský, BI Cho, H-K Chung, GL Dakovski, K Engelhorn, V Hájková, P Heimann, M Holmes, L Juha, J Krzywinski, RW Lee, S Toleikis, JJ Turner, U Zastrau, JS Wark

The effect of a dense plasma environment on the energy levels of an embedded ion is usually described in terms of the lowering of its continuum level. For strongly coupled plasmas, the phenomenon is intimately related to the equation of state; hence, an accurate treatment is crucial for most astrophysical and inertial-fusion applications, where the case of plasma mixtures is of particular interest. Here we present an experiment showing that the standard density-dependent analytical models are inadequate to describe solid-density plasmas at the temperatures studied, where the reduction of the binding energies for a given species is unaffected by the different plasma environment (ion density) in either the element or compounds of that species, and can be accurately estimated by calculations only involving the energy levels of an isolated neutral atom. The results have implications for the standard approaches to the equation of state calculations.


Detailed model for hot-dense aluminum plasmas generated by an x-ray free electron laser

PHYSICS OF PLASMAS 23 (2016) ARTN 022707

O Ciricosta, SM Vinko, H-K Chung, C Jackson, RW Lee, TR Preston, DS Rackstraw, JS Wark

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