Publications


Magnetic field generation by Biermann battery and Weibel instability in laboratory shock waves

EAS Publications Series 58 (2012) 23-26

G Gregori, F Miniati, B Reville, RP Drake

Magnetic field generation in the Universe is still an open problem. Possible mechanisms involve the Weibel instability, due to anisotropic phase-space distributions, as well as the Biermann battery, due to misaligned density and temperature gradients. These mechanisms can be reproduced in scaled laboratory experiments. In this contribution we estimate the relative importance of these two processes and explore the laser-energy requirements for producing Weibel dominated shocks. © The Author(s) 2013.


Quantum hydrodynamics of strongly coupled electron fluids

PHYSICAL REVIEW E 85 (2012) ARTN 046408

R Schmidt, BJB Crowley, J Mithen, G Gregori


Comparative merits of the memory function and dynamic local-field correction of the classical one-component plasma

PHYSICAL REVIEW E 85 (2012) ARTN 056407

JP Mithen, J Daligault, G Gregori


Employing laser-accelerated proton beams to diagnose high intensity laser-plasma interactions

AIP Conference Proceedings 1462 (2012) 149-154

G Sarri, CA Cecchetti, K Quinn, PA Norreys, R Trines, O Willi, J Fuchs, P McKenna, M Quinn, F Pegoraro, SV Bulanov, M Borghesi

A review of the proton radiography technique will be presented. This technique employs laser-accelerated laminar bunches of protons to diagnose the temporal and spatial characteristic of the electric and magnetic fields generated during high-intensity laser-plasma interactions. The remarkable temporal and spatial resolution that this technique can achieve (of the order of a picosecond and a few microns respectively) candidates this technique as the preferrable one, if compared to other techniques, to probe high intensity laser-matterinteractions. © 2012 American Institute of Physics.


Characterizing counter-streaming interpenetrating plasmas relevant to astrophysical collisionless shocks

Physics of Plasmas 19 (2012)

JS Ross, SH Glenzer, P Amendt, R Berger, L Divol, NL Kugland, OL Landen, C Plechaty, B Remington, D Ryutov, W Rozmus, DH Froula, G Fiksel, C Sorce, Y Kuramitsu, T Morita, Y Sakawa, H Takabe, RP Drake, M Grosskopf, C Kuranz, G Gregori, J Meinecke, CD Murphy, M Koenig, A Pelka, A Ravasio, T Vinci, E Liang, R Presura, A Spitkovsky, F Miniati, HS Park

A series of Omega experiments have produced and characterized high velocity counter-streaming plasma flows relevant for the creation of collisionless shocks. Single and double CH2 foils have been irradiated with a laser intensity of ∼ 1016 W/cm2. The laser ablated plasma was characterized 4 mm from the foil surface using Thomson scattering. A peak plasma flow velocity of 2000 km/s, an electron temperature of ∼ 110 eV, an ion temperature of ∼ 30 eV, and a density of ∼ 1018 cm -3 were measured in the single foil configuration. Significant increases in electron and ion temperatures were seen in the double foil geometry. The measured single foil plasma conditions were used to calculate the ion skin depth, c/ωpi ∼ 0.16 mm, the interaction length, lint, of ∼ 8 mm, and the Coulomb mean free path, λmfp ∼ 27 mm. With c/ωpi ≪ l int ≪λmfp, we are in a regime where collisionless shock formation is possible. © 2012 American Institute of Physics.


Extent of validity of the hydrodynamic description of ions in dense plasmas.

Phys Rev E Stat Nonlin Soft Matter Phys 83 (2011) 015401-

JP Mithen, J Daligault, G Gregori

We show that the hydrodynamic description can be applied to modeling the ionic response in dense plasmas for a wide range of length scales that are experimentally accessible. Using numerical simulations for the Yukawa model, we find that the maximum wave number k(max) at which the hydrodynamic description applies is independent of the coupling strength, given by k(max)λ(s)≃0.43, where λ(s) is the ionic screening length. Our results show that the hydrodynamic description can be used for interpreting x-ray scattering data from fourth generation light sources and high power lasers. In addition, our investigation sheds new light on how the domain of validity of the hydrodynamic description depends on both the microscopic properties and the thermodynamic state of fluids in general.


Numerical simulation of plasma-based raman amplification of laser pulses to petawatt powers

IEEE Transactions on Plasma Science 39 (2011) 2622-2623

RMGM Trines, F Fiuza, RA Fonseca, LO Silva, R Bingham, RA Cairns, PA Norreys

Contemporary high-power laser systems make use of solid-state laser technology to reach petawatt pulse powers. The breakdown threshold for optical components in these systems, however, demands beam diameters up to 1 m. Raman amplification of laser beams promises a breakthrough by the use of much smaller amplifying media, i.e., millimeter-diameter-wide plasmas. Through the first large-scale multidimensional particle-in-cell simulations of this process, we have identified the parameter regime where multipetawatt peak laser powers can be reached, while the influence of damaging laser-plasma instabilities is only minor. Snapshots of the probe laser pulse being amplified, generated using state-of-the-art visualization techniques, are presented. © 2006 IEEE.


X-ray scattering as a probe for warm dense mixtures and high-pressure miscibility

EPL 94 (2011)

K Wünsch, J Vorberger, G Gregori, DO Gericke

We develop a new theoretical approach that demonstrates the abilities of elastic X-ray scattering to yield thermodynamic, structural, and mixing properties of dense matter with multiple ion species. The novel decomposition of the electron structure factor in multi-component systems provides the basis to study dense mixtures as found in giant gas planets or during inertial confinement fusion. We show that the scattering signal differs significantly between single species, microscopic mixtures, and phase-separated fluids. Thus, these different phases can be distinguished experimentally via elastic X-ray scattering. © 2011 Europhysics Letters Association.


Vibrational excitation induced by electron beam and cosmic rays in normal and superconductive aluminum bars

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 659 (2011) 289-298

M Bassan, B Buonomo, G Cavallari, E Coccia, S Dantonio, V Fafone, LG Foggetta, C Ligi, A Marini, G Mazzitelli, G Modestino, G Pizzella, L Quintieri, F Ronga, P Valente, SM Vinko

We report new measurements of the acoustic excitation of an Al5056 superconductive bar when hit by an electron beam, in a previously unexplored temperature range, down to 0.35 K. These data, analyzed together with previous results of a dedicated experiment obtained for T >0.54K, show a vibrational response enhanced by a factor ∼4.9 with respect to that measured in the normal state. This enhancement explains the anomalous large signals due to cosmic rays previously detected in the NAUTILUS gravitational wave detector. © 2011 Elsevier B.V. All rights reserved.


Simulations of neon irradiated by intense X-ray laser radiation

High Energy Density Physics 7 (2011) 111-116

O Ciricosta, HK Chung, RW Lee, JS Wark

We present simulations of the charge states produced by the interaction of intense X-ray laser radiation with a neon gas. We model the results of a recent experiment (Young et al., Nature 466, 56 (2010)), where mJ pulses of X-rays, with photon energies ranging from 800 to 2000 eV and pulse lengths ranging from 70 to 340 fs were incident on neon atoms at intensities of up to 10 18 W cm -2. Simulations using an adapted version of the SCFLY collisional-radiative code, which included the effect of electron collisions and a simple self-consistent temperature model, result in charge state distributions that are in good agreement with the experimental data. We calculate the electron temperature of the system during the evolution of the plasma, and comment upon the role that collisions may play in determining the charge state distributions as a function of the neon ion number density. © 2011 Elsevier B.V.


TOF-OFF: A method for determining focal positions in tightly focused free-electron laser experiments by measurement of ejected ions

High Energy Density Physics 7 (2011) 336-342

B Iwan, J Andreasson, A Andrejczuk, E Abreu, M Bergh, C Caleman, AJ Nelson, S Bajt, J Chalupsky, HN Chapman, RR Fäustlin, V Hajkova, PA Heimann, B Hjörvarsson, L Juha, D Klinger, J Krzywinski, B Nagler, GK Pálsson, W Singer, MM Seibert, R Sobierajski, S Toleikis, T Tschentscher, SM Vinko, RW Lee, J Hajdu, N Tîmneanu

Pulse intensities greater than 1017 Watt/cm2 were reached at the FLASH soft X-ray laser in Hamburg, Germany, using an off-axis parabolic mirror to focus 15 fs pulses of 5-70 μJ energy at 13.5 nm wavelength to a micron-sized spot. We describe the interaction of such pulses with niobium and vanadium targets and their deuterides. The beam produced craters in the solid targets, and we measured the kinetic energy of ions ejected from these craters. Ions with several keV kinetic energy were observed from craters approaching 5 μm in depth when the sample was at best focus. We also observed the onset of saturation in both ion acceleration and ablation with pulse intensities exceeding 1016 W/cm2, when the highest detected ion energies and the crater depths tend to saturate with increasing intensity. A general difficulty in working with micron and sub-micron focusing optics is finding the exact focus of the beam inside a vacuum chamber. Here we propose a direct method to measure the focal position to a resolution better than the Rayleigh length. The method is based on the correlation between the energies of ejected ions and the physical dimensions of the craters. We find that the focus position can be quickly determined from the ion time-of-flight (TOF) data as the target is scanned through the expected focal region. The method does not require external access to the sample or venting the vacuum chamber. Profile fitting employed to analyze the TOF data can extend resolution beyond the actual scanning step size. © 2011 Elsevier B.V.


High-power, kilojoule class laser channeling in millimeter-scale underdense plasma

Physical Review Letters 106 (2011)

L Willingale, PM Nilson, AGR Thomas, J Cobble, RS Craxton, A Maksimchuk, PA Norreys, TC Sangster, RHH Scott, C Stoeckl, C Zulick, K Krushelnick

Experiments were performed using the Omega EP laser, operating at 740 J of energy in 8 ps (90 TW), which provides extreme conditions relevant to fast ignition studies. A carbon and hydrogen plasma plume was used as the underdense target and the interaction of the laser pulse propagating and channeling through the plasma was imaged using proton radiography. The early time expansion, channel evolution, filamentation, and self-correction of the channel was measured on a single shot via this method. A channel wall modulation was observed and attributed to surface waves. After around 50 ps, the channel had evolved to show bubblelike structures, which may be due to postsoliton remnants. © 2011 American Physical Society.


A Vlasov-Fokker-Planck code for high energy density physics

JOURNAL OF COMPUTATIONAL PHYSICS 230 (2011) 6475-6494

M Tzoufras, AR Bell, PA Norreys, FS Tsung


Spectroscopic studies of hard x-ray free-electron laser-heated foils at 10(16) Wcm(-2) irradiances

X-RAY LASERS AND COHERENT X-RAY SOURCES: DEVELOPMENT AND APPLICATIONS IX 8140 (2011)

J Dunn, R Shepherd, A Graf, A Steel, J Park, SJ Moon, RW Lee, P Audebert, A Levy, M Gauthier, J Fuchs, DM Fritz, M Cammarata, D Milathianaki, HJ Lee, B Nagler, C Fourment, F Deneuville, G Williams, M Fajardo, J Gaudin, S Vinko, O Ciricosta, J Wark, HK Chung


Vibrational excitation induced by electron beam and cosmic rays in normal and superconductive aluminum bars

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment (2011)

M Bassan, B Buonomo, G Cavallari, E Coccia, S D'Antonio, V Fafone, LG Foggetta, C Ligi, A Marini, G Mazzitelli, G Modestino, G Pizzella, L Quintieri, F Ronga, P Valente, SM Vinko


In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy

JOURNAL OF INSTRUMENTATION 6 (2011) ARTN P10001

U Zastrau, V Hilbert, C Brown, T Doeppner, S Dziarzhytski, E Foerster, SH Glenzer, S Goede, G Gregori, M Harmand, D Hochhaus, T Laarmann, HJ Lee, K-H Meiwes-Broer, P Neumayer, A Przystawik, P Radcliffe, M Schulz, S Skruszewicz, F Tavella, J Tiggesbaeumker, S Toleikis, T White


Spectroscopic studies of hard x-ray free-electron laser-heated foils at 10 16 Wcm -2 irradiances

Proceedings of SPIE - The International Society for Optical Engineering 8140 (2011)

J Dunn, R Shepherd, A Graf, A Steel, J Park, SJ Moon, RW Lee, P Audebert, A Levy, M Gauthier, J Fuchs, DM Fritz, M Cammarata, D Milathianaki, HJ Lee, B Nagler, C Fourment, F Deneuville, G Williams, M Fajardo, J Gaudin, S Vinko, O Ciricosta, J Wark, HK Chung

We report a recent experiment where the first hard x-ray beam line, X-ray Pump Probe (XPP) instrument using the SLAC National Accelerator Laboratory's Linac Coherent Light Source (LCLS) free electron laser, was used to heat thin foils to high energy densities ∼ 107 J/cm 3. An intense 9 keV, 60 fs (FWHM) duration beam with energy of 2 - 4 mJ at the XPP beam line was focused using beryllium lenses to an irradiance approaching 1016 Wcm -2. Targets of 0.5 - 3.5 μm thick foils of Ag and Cu were studied using a suite of diagnostics including Fourier Domain Interferometry, energy calorimetry and grating and crystal spectrometers. The experimental details and spectroscopic results from the campaign will be described. Preliminary results indicate that the target is heated relatively uniformly to a temperature lower than 20 eV. © 2011 SPIE.


In-situ determination of dispersion and resolving power in simultaneous multiple-angle XUV spectroscopy

Journal of Instrumentation 6 (2011)

U Zastrau, V Hilbert, C Brown, T Döppner, S Dziarzhytski, E Förster, H Glenzer, S Göde, G Gregori, M Harmand, D Hochhaus, T Laarmann, J Lee, KH Meiwes-Broer, P Neumayer, A Przystawik, P Radcliffe, M Schulz, S Skruszewicz, F Tavella, J Tiggesbäumker, S Toleikis, T White

We report on the simultaneous determination of non-linear dispersion functions and resolving power of three flat-field XUV grating spectrometers. A moderate-intense short-pulse infrared laser is focused onto technical aluminum which is commonly present as part of the experimental setup. In the XUV wavelength range of 10-19 nm, the spectrometers are calibrated using Al-Mg plasma emission lines. This cross-calibration is performed in-situ in the very same setup as the actual main experiment. The results are in excellent agreement with ray-tracing simulations. We show that our method allows for precise relative and absolute calibration of three different XUV spectrometers. © 2011 IOP Publishing Ltd and SISSA.


Experimental results performed in the framework of the HiPER European Project

Proceedings of SPIE - The International Society for Optical Engineering 8080 (2011)

D Batani, M Koenig, S Baton, F Perez, LA Gizzi, P Koester, L Labate, J Honrubia, A Debayle, J Santos, G Schurtz, S Hulin, X Ribeyre, C Fourment, P Nicolai, B Vauzour, L Gremillet, W Nazarov, J Pasley, G Tallents, M Richetta, K Lancaster, C Spindloe, M Tolley, D Neely, P Norreys, M Kozlová, J Nejdl, B Rus, L Antonelli, A Morace, L Volpe, J Davies, J Wolowski, J Badziak

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to "Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future reactors, and making fusion possible with smaller facilities. In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France) Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling in the 1016 W/cm2 intensity regime of interest for Shock Ignition. © 2011 SPIE.


K-shell spectroscopy of Au plasma generated with a short-pulse laser

Canadian Journal of Physics 89 (2011) 647-651

C Zulick, F Dollar, H Chen, K Falk, G Gregori, A Hazi, CD Murphy, J Park, J Seely, CI Szabo, R Tommasini, R Shepherd, K Krushelnick

The production of X-rays from electron transitions into K-shell vacancies (Kα,β) emission) is a well-known process in atomic physics and has been extensively studied as a plasma diagnostic in low-and mid-Z materials. However, X-ray spectra from near neutral high-Z ions are very complex, and their interpretation requires the use of state-of-the-art atomic calculations. In this experiment, the Titan laser system at Lawrence Livermore National Laboratory was used to deliver an approximately 350 J laser pulse, with a 10 ps duration and a wavelength of 1054 nm, to a gold (Au) target. A transparent bent quartz crystal spectrometer with a hard X-ray energy window, ranging from 17 to 102 keV, was used to measure the emission spectrum. Kα1,α2 and Kβ1,γ1 transitions were observed over a range of target sizes. Additionally, a series of shots were conducted with a pre-ionizing long pulse (3 ns, 1-10 J, 527 nm) on the backside of the target. FLYCHK, an atomic non-LTE code, designed to provide ionization and population distributions, was used to model the experiment. K α/Kβ ratios were found to be in good agreement with the predicted value for room temperature Au targets. © 2011 Published by NRC Research Press.