Publications


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.


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


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


Measuring fast electron distribution functions at intensities up to 10 21 W cm-2

Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 653 (2011) 137-139

N Booth, N Booth, RJ Clarke, D Doria, LA Gizzi, G Gregori, P Hakel, P Koester, L Labate, T Levato, B Li, M Makita, RC Mancini, J Pasley, J Pasley, PP Rajeev, D Riley, APL Robinson, E Wagenaars, JN Waugh, NC Woolsey

Here we present results from ultra-intense experiments demonstrating the viability of polarization spectroscopy as a diagnostic of the electron return current and spatial anisotropy and distribution function of the fast electron beam. The measurements extend to ultra-relativistic intensities of 10 21 W cm-2, including laserplasma interaction regimes important for fast ignition studies, for example HiPER, and the development of secondary sources from next generation ultra-short pulse, ultra-intense laser facilities such as Astra-Gemini and ELI. As an in situ diagnostic, spectroscopic measurements are vital to understanding fast electron beams, enabling extrapolation of results to define fast ignition inertial confinement fusion and secondary source facilities. © 2011 Elsevier B.V.


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

ArXiv (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

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 the RAP experiment obtained for T > 0.54 K, 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.


Simulations of copper single crystals subjected to rapid shear

Journal of Applied Physics 109 (2011)

A Higginbotham, EM Bringa, J Marian, N Park, M Suggit, JS Wark

We report on nonequilibrium molecular dynamics simulations of single crystals of copper experiencing rapid shear strain. A model system, with periodic boundary conditions, which includes a single dislocation dipole is subjected to a total shear strain of close to 10 on time-scales ranging from the instantaneous to 50 ps. When the system is strained on a time-scale short compared with a phonon period, the initial total applied shear is purely elastic, and the eventual temperature rise in the system due to the subsequent plastic work can be determined from the initial elastic strain energy. The rate at which this plastic work occurs, and heat is generated, depends on the dislocation velocity, which itself is a function of shear stress. A determination of the stress-dependence of the dislocation velocity allows us to construct a simple analytic model for the temperature rise in the system as a function of strain rate, and this model is found to be in good agreement with the simulations. For the effective dislocation density within the simulations, 7.8 10 11 cm - 2, we find that applying the total shear strain on time-scales of a few tens of picoseconds greatly reduces the final temperature. We discuss these results in the context of the growing interest in producing high pressure, solid-state matter, by quasi-isentropic (rather than shock) compression. © 2011 American Institute of Physics.


Decay of Cystalline Order and Equilibration during the Solid-to-Plasma Transition Induced by 20-fs Microfocused 92-eV Free-Electron-Laser Pulses

PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS 14 (2011) ARTN 164801

E Galtier, FB Rosmej, T Dzelzainis, D Riley, FY Khattak, P Heimann, RW Lee, AJ Nelson, SM Vinko, T Whitcher, JS Wark, T Tschentscher, S Toleikis, RR Faeustlin, R Sobierajski, M Jurek, L Juha, J Chalupsky, V Hajkova, M Kozlova, J Krzywinski, B Nagler


Investigation of fast electron energy coupling in a counter-propagating scheme

38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts 35 2 (2011) 1484-1487

P Koester, P Koester, N Booth, CA Cecchetti, CA Cecchetti, H Chen, RG Evans, G Gregori, L Labate, L Labate, T Levato, B Li, M Makita, J Mithen, C Murphy, M Notley, R Pattathil, D Riley, N Woolsey, LA Gizzi, LA Gizzi

A detailed knowledge of the physical phenomena underlying the transport of fast electrons generated in high-intensity laser-matter interactions is of fundamental importance for the fast ignition scheme for inertial confinement fusion. The fast electron currents largely exceed the Alfven limit, therefore a balancing return current is required to support the propagation of the fast electron beam in the target medium. An experimental study aimed at investigating the role of the return current on the dynamics of the fast electron beam was carried out with the Vulcan Petawatt beam. Two counter-propagating electron beams were generated by double-sided irradiation of a layered target containing a 5 micron thick Ti layer. Information on the energy coupling of the fast electron beam to the Ti layer was retrieved through X-ray measurements. In particular, high-resolution X-ray spectroscopy of the Ti emission lines was performed in the spectral range from 4.4 to 5.1 keV including the Lyα, the Heα and the Kα line. Spectra were acquired for double-sided irradiation with different timings between the two laser beams as well as for single-sided irradiation. The recorded spectra indicate a higher target temperature for a precise timing between the two beams in agreement with simulation results.


Proton radiography of intense-laser-irradiated wire-attached cone targets

IEEE Transactions on Plasma Science 39 (2011) 2822-2823

T Yabuuchi, H Sawada, T Bartal, D Batani, LA Gizzi, MH Key, AJ MacKinnon, HS McLean, PA Norreys, PK Patel, RB Stephens, C Spindloe, W Theobald, MS Wei, FN Beg

Measurements of extreme electrostatic and magnetic fields are of interest for the study of high-energy-density plasmas. Results of proton deflectometry of cone-wire targets that are of interest to fast-ignition inertial confinement fusion are presented. © 2006 IEEE.


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, 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.


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, 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, 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.


The strength of single crystal copper under uniaxial shock compression at 100 GPa.

J Phys Condens Matter 22 (2010) 065404-

WJ Murphy, A Higginbotham, G Kimminau, B Barbrel, EM Bringa, J Hawreliak, R Kodama, M Koenig, W McBarron, MA Meyers, B Nagler, N Ozaki, N Park, B Remington, S Rothman, SM Vinko, T Whitcher, JS Wark

In situ x-ray diffraction has been used to measure the shear strain (and thus strength) of single crystal copper shocked to 100 GPa pressures at strain rates over two orders of magnitude higher than those achieved previously. For shocks in the [001] direction there is a significant associated shear strain, while shocks in the [111] direction give negligible shear strain. We infer, using molecular dynamics simulations and VISAR (standing for 'velocity interferometer system for any reflector') measurements, that the strength of the material increases dramatically (to approximately 1 GPa) for these extreme strain rates.


Electron bunch length measurements from laser-accelerated electrons using single-shot thz time-domain interferometry

Physical Review Letters 104 (2010)

AD Debus, M Bussmann, U Schramm, R Sauerbrey, CD Murphy, Z Major, Z Major, R Hörlein, R Hörlein, L Veisz, K Schmid, J Schreiber, J Schreiber, J Schreiber, K Witte, SP Jamison, JG Gallacher, DA Jaroszynski, MC Kaluza, B Hidding, S Kiselev, R Heathcote, PS Foster, D Neely, EJ Divall, CJ Hooker, JM Smith, K Ertel, AJ Langley, P Norreys, JL Collier, S Karsch, S Karsch

Laser-plasma wakefield-based electron accelerators are expected to deliver ultrashort electron bunches with unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment. We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5 J, 45 fs, 800 nm laser and a ZnTe-based electro-optical setup, we demonstrate the duration of laser-accelerated, quasimonoenergetic electron bunches [best fit of 32 fs (FWHM) with a 90% upper confidence level of 38 fs] to be shorter than the drive laser pulse, but similar to the plasma period. © 2010 The American Physical Society.


Bragg diffraction using a 100 ps 17.5 keV x-ray backlighter and the Bragg diffraction imager

REVIEW OF SCIENTIFIC INSTRUMENTS 81 (2010)

BR Maddox, H-S Park, J Hawreliak, A Elsholz, R Van Maren, BA Remington, A Comley, JS Wark


Magnetic collimation of petawatt driven fast electron beam for prospective fast ignition studies

Journal of Physics: Conference Series 244 (2010)

S Kar, D Adams, M Borghesi, K Markey, B Ramakrishna, M Zepf, K Lancaster, P Norreys, APL Robinson, DC Carroll, P McKenna, M Quinn, X Yuan, C Bellei, J Schreiber

Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations. © 2010 IOP Publishing Ltd.


Soft X-ray scattering using FEL radiation for probing near-solid density plasmas at few electron volt temperatures

High Energy Density Physics 6 (2010) 15-20

S Toleikis, RR Fäustlin, L Cao, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, J Mithen, KH Meiwes-Broer, A Przystawik, P Radcliffe, R Redmer, F Tavella, R Thiele, J Tiggesbäumker, NX Truong, I Uschmann, U Zastrau, T Tschentscher

We report on soft X-ray scattering experiments on cryogenic hydrogen and simple metal samples. As a source of intense, ultrashort soft X-ray pulses we have used free-electron laser radiation at 92 eV photon energy from FLASH at DESY, Hamburg. X-ray pulses with energies up to 150 μJ and durations 15-50 fs provide interaction with the sample leading simultaneously to plasma formation and scattering. Experiments exploiting both of these interactions have been carried out, using the same experimental setup. Firstly, recording of soft X-ray inelastic scattering from near-solid density hydrogen plasmas at few electron volt temperatures confirms the feasibility of this diagnostics technique. Secondly, the soft X-ray excitation of few electron volt solid-density plasmas in bulk metal samples could be studied by recording soft X-ray line and continuum emission integrated over emission times from fs to ns. © 2009 Elsevier B.V.


Micron-scale fast electron filaments and recirculation determined from rear-side optical emission in high-intensity laser-solid interactions

New Journal of Physics 12 (2010)

C Bellei, SR Nagel, S Kar, A Henig, A Henig, S Kneip, C Palmer, A Sävert, L Willingale, L Willingale, D Carroll, B Dromey, JS Green, JS Green, K Markey, P Simpson, RJ Clarke, H Lowe, D Neely, C Spindloe, M Tolley, MC Kaluza, MC Kaluza, SPD Mangles, P McKenna, PA Norreys, PA Norreys, J Schreiber, J Schreiber, J Schreiber, M Zepf, JR Davies, K Krushelnick, K Krushelnick, Z Najmudin

The transport of relativistic electrons generated in the interaction of petawatt class lasers with solid targets has been studied through measurements of the second harmonic optical emission from their rear surface. The high degree of polarization of the emission indicates that it is predominantly optical transition radiation (TR). A halo that surrounds the main region of emission is also polarized and is attributed to the effect of electron recirculation. The variation of the polarization state and intensity of radiation with the angle of observation indicates that the emission of TR is highly directional and provides evidence for the presence of μm-size filaments. A brief discussion on the possible causes of such a fine electron beam structure is given. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.


Measurement of fast electrons spectra generated by interaction between solid target and peta watt laser

Journal of Physics: Conference Series 244 (2010)

T Tanimoto, H Habara, KA Tanaka, R Kodama, M Nakatsutsumi, KL Lancaster, JS Green, RHH Scott, RHH Scott, M Sherlock, M Sherlock, PA Norreys, PA Norreys, RG Evans, MG Haines, S Kar, M Zepf, J King, T Ma, MS Wei, T Yabuuchi, FN Beg, MH Key, P Nilson, RB Stephens, H Azechi, K Nagai, T Norimatsu, K Takeda, J Valente, JR Davies

Fast electron energy spectra have been measured for a range of intensities between 1018 Wcm-2 and 1021 Wcm-2 and for different target materials using electron spectrometers. Several experimental campaigns were conducted on peta watt laser facilities at the Rutherford Appleton Laboratory and Osaka University. In these experimental campaigns, the pulse duration was varied from 0.5 ps to 5 ps. The laser incident angle was also changed from normal incidence to 40° in p-polarized. The results show a reduction from the ponderomotive scaling on fast electrons over 1020 Wcm-2. © 2010 IOP Publishing Ltd.


Design of the 10 PW OPCPA facility for the Vulcan laser

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

I Musgrave, O Chekhlov, J Collier, R Clarke, A Dunne, S Hancock, R Heathcote, C Hernandez-Gomez, M Galimberti, A Lyachev, P Matousek, D Neely, P Norreys, I Ross, Y Tang, T Winstone, G New

We present the progress made in developing IOPW OPCPA facility for the Vulcan laser to produce pulses with focused intensities >1023 Wcm-2. This power level will be delivered by generating pulses with >300J in 30fs. These pulses will be delivered to two target areas: in one target area they will be combined with the existing Vulcan Petawatt beamline and a new target area will be created for high intensity interactions. © 2010 Optical Society of America.


Observation of ultrafast nonequilibrium collective dynamics in warm dense hydrogen.

Phys Rev Lett 104 (2010) 125002-

RR Fäustlin, T Bornath, T Döppner, S Düsterer, E Förster, C Fortmann, SH Glenzer, S Göde, G Gregori, R Irsig, T Laarmann, HJ Lee, B Li, KH Meiwes-Broer, J Mithen, B Nagler, A Przystawik, H Redlin, R Redmer, H Reinholz, G Röpke, F Tavella, R Thiele, J Tiggesbäumker, S Toleikis, I Uschmann, SM Vinko, T Whitcher, U Zastrau, B Ziaja, T Tschentscher

We investigate ultrafast (fs) electron dynamics in a liquid hydrogen sample, isochorically and volumetrically heated to a moderately coupled plasma state. Thomson scattering measurements using 91.8 eV photons from the free-electron laser in Hamburg (FLASH at DESY) show that the hydrogen plasma has been driven to a nonthermal state with an electron temperature of 13 eV and an ion temperature below 0.1 eV, while the free-electron density is 2.8x10{20} cm{-3}. For dense plasmas, our experimental data strongly support a nonequilibrium kinetics model that uses impact ionization cross sections based on classical free-electron collisions.