Publications


Scaled laboratory experiments explain the kink behaviour of the Crab Nebula jet

Nature Communications Nature Publishing Group (2016)

CK Li, P Tzeferacos, D Lamb, G Gregori, PA Norreys, MJ Rosenberg, RK Follett, DH Froula, M Koenig, FH Seguin, JA Frenje, HG Rinderknecht, H Sio, AB Zylstra, RD Petrasso, PA Amendt, HS Park, BA Remington, SX Hu, TC Sangster, P Hartigan, RP Drake, CC Kuranz, SV Lebedev, NC Woolsey

The remarkable discovery by the Chandra X-ray observatory that the Crab nebula's jet periodically changes direction provides a challenge to our understanding of astrophysical jet dynamics. It has been suggested that this phenomenon may be the consequence of magnetic fields and magnetohydrodynamic instabilities, but experimental demonstration in a controlled laboratory environment has remained elusive. Here we report experiments that use high-power lasers to create a plasma jet that can be directly compared with the Crab jet through well-defined physical scaling laws. The jet generates its own embedded toroidal magnetic fields; as it moves, plasma instabilities result in multiple deflections of the propagation direction, mimicking the kink behaviour of the Crab jet. The experiment is modelled with three-dimensional numerical simulations that show exactly how the instability develops and results in changes of direction of the jet.


Short-pulse laser-driven x-ray radiography

High Power Laser Science and Engineering Cambridge University Press 4 (2016) e30-

E Brambrink, S Baton, M Koenig, R Yurchak, N Bidaut, B Albertazzi, JE Cross, G Gregori, A Rigby, E Falize, A Pelka, F Kroll, S Pikuz, Y Sakawa, N Ozaki, C Kuranz, M Manuel, C Li, P Tzeferacos, D Lamb

We have developed a new radiography setup with a short-pulse laser-driven x-ray source. Using a radiography axis perpendicular to both long- and short-pulse lasers allowed optimizing the incident angle of the short-pulse laser on the x-ray source target. The setup has been tested with various x-ray source target materials and different laser wavelengths. Signal to noise ratios are presented as well as achieved spatial resolutions. The high quality of our technique is illustrated on a plasma flow radiograph obtained during a laboratory astrophysics experiment on POLARs.


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

Nature Communications Nature Publishing Group 7 (2016) ncomms11899-

JE Cross, G Gregori, JM Foster, P Graham, JM 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 and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment Elsevier 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

The most established route to create a laser-based neutron source is by employing laser accelerated, low atomic-number ions in fusion reactions. In addition to the high reaction cross-sections at moderate energies of the projectile ions, the anisotropy in neutron emission is another important feature of beam-fusion reactions. Using a simple numerical model based on neutron generation in a pitcher–catcher scenario, anisotropy in neutron emission was studied for the deuterium–deuterium fusion reaction. Simulation results are consistent with the narrow-divergence (∼70° full width at half maximum) neutron beam recently served in an experiment employing multi-MeV deuteron beams of narrow divergence (up to 30° FWHM, depending on the ion energy) accelerated by a sub-petawatt laser pulse from thin deuterated plastic foils via the Target Normal Sheath Acceleration mechanism. By varying the input ion beam parameters, simulations show that a further improvement in the neutron beam directionality (i.e. reduction in the beam divergence) can be obtained by increasing the projectile ion beam temperature and cut-off energy, as expected from interactions employing higher power lasers at upcoming facilities.


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

Nature Communications Nature Publishing Group 7 (2016) 11713-

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

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.


AWAKE, The Advanced Proton Driven Plasma Wakefield Acceleration Experiment at CERN

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT 829 (2016) 76-82

E Gschwendtner, E Adli, L Amorim, R Apsimon, R Assmann, A-M Bachmann, F Batsch, J Bauche, VKB Olsen, M Bernardini, R Bingham, B Biskup, T Bohl, C Bracco, PN Burrows, G Burt, B Buttenschoen, A Butterworth, A Caldwell, M Cascella, E Chevallay, S Cipiccia, H Damerau, L Deacon, R Dirksen, S Doebert, U Dorda, J Farmer, V Fedosseev, E Feldbaumer, R Fiorito, R Fonseca, F Friebel, AA Gorn, O Grulke, J Hansen, C Hessler, W Hofle, J Holloway, M Huether, D Jaroszynski, L Jensen, S Jolly, A Joulaei, M Kasim, F Keeble, Y Li, S Liu, N Lopes, KV Lotov, S Mandry, R Martorelli, M Martyanov, S Mazzoni, O Mete, VA Minakov, J Mitchell, J Moody, P Muggli, Z Najmudin, R Norreys, E Oez, A Pardons, K Pepitone, A Petrenko, G Plyushchev, A Pukhov, K Rieger, H Ruhl, E Salveter, N Savard, J Schmidt, A Seryi, E Shaposhnikova, ZM Sheng, R Sherwood, L Silva, L Soby, AP Sosedkin, RI Spitsyn, R Trines, PV Tuev, M Turner, V Verzilov, J Vieira, H Vincke, Y Wei, CP Welsch, M Wing, G Xia, H Zhang


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

Physical Review American Physical Society 94 (2016) 023203-

B Kettle, T Dzelzainis, S White, L Li, B Dromey, M Zepf, CL 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.


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 National Academy of Sciences 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.


Magnetic field generation during intense laser channelling in underdense plasma

Physics of Plasmas AIP Publishing 23 (2016)

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

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.


Characteristics of betatron radiation from direct-laser accelerated electrons

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics American Physical Society 93 (2016) 063203

TW Huang, APL Robinson, C-T Zhou, B Qiao, B Liu, R Shang-Chen, H Xian-Tu, P 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(≡ne/nca0). Both the electron transverse momentum and energy are proportional to the normalized amplitude of laser field (a0) for a fixed value of S. As a result, the total number of radiated photons scales as a2/0/√S and the energy conversion efficiency of photons from the accelerated electrons scales as a3/0/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.


Characteristics of betatron radiation from direct-laser-accelerated electrons

Physical Review E American Physical Society 93 (2016) 063203

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


Mitigating the hosing instability in relativistic laser-plasma interactions

New Journal of Physics Institute of Physics 18 (2016) 053023-

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

A new physical model of the hosing instability that includes relativistic laser pulses and moderate densities is presented and derives the density dependence of the hosing equation. This is tested against two-dimensional particle-in-cell simulations. These simulations further examine the feasibility of using multiple pulses to mitigate the hosing instability in a Nd:glass-type parameter space. An examination of the effects of planar versus cylindrical exponential density gradients on the hosing instability is also presented. The results show that strongly relativistic pulses and more planar geometries are capable of mitigating the hosing instability which is in line with the predictions of the physical model.


Beamed neutron emission driven by laser accelerated light ions

New Journal of Physics IOP Publishing (2016)

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

Highly anisotropic, beam-like neutron emission with peak flux of the order of 109 n/sr was obtained from light nuclei reactions in a pitcher–catcher scenario, by employing MeV ions driven by a sub-petawatt laser. The spatial profile of the neutron beam, fully captured for the first time by employing a CR39 nuclear track detector, shows a FWHM divergence angle of $\sim 70^\circ $, with a peak flux nearly an order of magnitude higher than the isotropic component elsewhere. The observed beamed flux of neutrons is highly favourable for a wide range of applications, and indeed for further transport and moderation to thermal energies. A systematic study employing various combinations of pitcher–catcher materials indicates the dominant reactions being d(p, n+p)1H and d(d,n)3He. Albeit insufficient cross-section data are available for modelling, the observed anisotropy in the neutrons' spatial and spectral profiles is most likely related to the directionality and high energy of the projectile ions.


Theory of Thomson scattering in inhomogeneous media

Scientific reports Nature Publishing Group 6 (2016) 24283-

PM Kozlowski, BJ Crowley, 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.


Sherlock et al. Reply

Physical Review Letters American Physical Society 116 (2016)

S Rose, M Sherlock, W Rozmus, EG Hill


Inelastic response of silicon to shock compression.

Scientific reports Nature Publishing Group 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, J 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.


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


Thomson scattering measurement of a collimated plasma jet generated by a high-power laser system

Journal of Physics: Conference Series IOP Publishing: Conference Series 688 (2016) 012098-

T Ishikawa, Y Sakawa, T Morita, Y Yamaura, Y Kuramitsu, T Moritaka, T Sano, R Shimoda, K Tomita, K Uchino, S Matsukiyo, A Mizuta, N Ohnishi, R Crowston, N Woolsey, H Doyle, G Gregori, M Koenig, C Michaut, A Pelka, D Yuan, K Zhang, J Zhong, F Wang, H Takabe

One of the important and interesting problems in astrophysics and plasma physics is collimation of plasma jets. The collimation mechanism, which causes a plasma flow to propagate a long distance, has not been understood in detail. We have been investigating a model experiment to simulate astrophysical plasma jets with an external magnetic field [Nishio et al., EPJ. Web of Conferences 59, 15005 (2013)]. The experiment was performed by using Gekko XII HIPER laser system at Institute of Laser Engineering, Osaka University. We shot CH plane targets (3 mm × 3 mm × 10 μm) and observed rear-side plasma flows. A collimated plasma flow or plasma jet was generated by separating focal spots of laser beams. In this report, we measured plasma jet structure without an external magnetic field with shadowgraphy, and simultaneously measured the local parameters of the plasma jet, i.e., electron density, electron and ion temperatures, charge state, and drift velocity, with collective Thomson scattering.


Spherical shock in the presence of an external magnetic field

Journal of Physics: Conference Series IOP Publishing: Conference Series 688 (2016) 012056-

Y Kuramitsu, S Matsukiyo, S Isayama, D Harada, T Oyama, R Fujino, Y Sakawa, T Morita, Y Yamaura, T Ishikawa, T Moritaka, T Sano, K Tomita, R Shimoda, Y Sato, K Uchino, A Pelka, R Crowston, N Woolsey, G Gregori, M Koenig, CL Yin, YT Li, K Zhang, H Takabe

We investigate spherical collisionless shocks in the presence of an external magnetic field. Spherical collisionless shocks are common resultant of interactions between a expanding plasma and a surrounding plasma, such as the solar wind, stellar winds, and supernova remnants. Anisotropies often observed in shock propagations and their emissions, and it is widely believed a magnetic field plays a major role. Since the local observations of magnetic fields in astrophysical plasmas are not accessible, laboratory experiments provide unique capability to investigate such phenomena. We model the spherical shocks in the universe by irradiating a solid spherical target surrounded by a plasma in the presence of a magnetic field. We present preliminary results obtained by shadowgraphy.


AWAKE: A Proton-Driven Plasma Wakefield Acceleration Experiment at CERN

Nuclear and Particle Physics Proceedings Elsevier (2016)

C Bracco, LD Amorim, R Assmann, F Batsch, R Bingham, G Burt, B Buttenschön, A Butterworth, A Caldwell, S Chattopadhyay, S Cipiccia, LC Deacon, S Doebert, U Dorda, E Feldbaumer, RA Fonseca, V Fedossev, B Goddard, J Grebenyuk, O Grulke, E Gschwendtner, J Hansen, C Hessler, W Hofle, J Holloway

© 2015 Elsevier B.V..The AWAKE Collaboration has been formed in order to demonstrate proton-driven plasma wakefield acceleration for the first time. This acceleration technique could lead to future colliders of high energy but of a much reduced length when compared to proposed linear accelerators. The CERN SPS proton beam in the CNGS facility will be injected into a 10 m plasma cell where the long proton bunches will be modulated into significantly shorter micro-bunches. These micro-bunches will then initiate a strong wakefield in the plasma with peak fields above 1 GV/m that will be harnessed to accelerate a bunch of electrons from about 20 MeV to the GeV scale within a few meters. The experimental program is based on detailed numerical simulations of beam and plasma interactions. The main accelerator components, the experimental area and infrastructure required as well as the plasma cell and the diagnostic equipment are discussed in detail. First protons to the experiment are expected at the end of 2016 and this will be followed by an initial three-four years experimental program. The experiment will inform future larger-scale tests of proton-driven plasma wakefield acceleration and applications to high energy colliders.

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