Publications by Gianluca Gregori

Investigation of the solid-liquid phase transition of carbon at 150GPa with spectrally resolved X-ray scattering

High Energy Density Physics 14 (2015) 38-43

J Helfrich, D Kraus, A Ortner, S Frydrych, GE Schaumann, NJ Hartley, G Gregori, B Kettle, D Riley, DC Carroll, MM Notley, C Spindloe, M Roth

© 2015 Elsevier B.V. We have resolved the solid-liquid phase transition of carbon at pressures around 150GPa. High-pressure samples of different temperatures were created by laser-driven shock compression of graphite and varying the initial density from 1.30g/cm3 to 2.25g/cm3. In this way, temperatures from 5700K to 14,500K could be achieved for relatively constant pressure according to hydrodynamic simulations. From measuring the elastic X-ray scattering intensity of vanadium K-alpha radiation at 4.95keVat a scattering angle of 126°, which is very sensitive to the solid-liquid transition, we can determine whether the sample had transitioned to the fluid phase. We find that samples of initial density 1.3g/cm3 and 1.85g/cm3 are liquid in the compressed states, whereas samples close to the ideal graphite crystal density of 2.25g/cm3 remain solid, probably in a diamond-like state.

Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams

PHYSICS OF PLASMAS 22 (2015) ARTN 020701

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

Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows

NATURE PHYSICS 11 (2015) 173-176

CM Huntington, F Fiuza, JS Ross, AB Zylstra, RP Drake, DH Froula, G Gregori, NL Kugland, CC Kuranz, MC Levy, CK Li, J Meinecke, T Morita, R Petrasso, C Plechaty, BA Remington, DD Ryutov, Y Sakawa, A Spitkovsky, H Takabe, H-S Park

Electron-ion temperature equilibration in warm dense tantalum

High Energy Density Physics 14 (2015) 1-5

NJ Hartley, PX Belancourt, DA Chapman, TD Döppner, PP Drake, DO Gericke, SH Glenzer, D Khaghani, SL Lepape, T Ma, PB Neumayer, A Pak, L Peters, SL Richardson, J Vorberger, TG White, G Gregori

© 2014 Elsevier B.V. We present measurements of electron-ion temperature equilibration in proton-heated tantalum, under warm dense matter conditions. Our results agree with theoretical predictions for metals calculated using input data from ab initio simulations. However, the fast relaxation observed in the experiment contrasts with much longer equilibration times found in proton heated carbon, indicating that the energy flow pathways in warm dense matter are far from being fully understood.



JE Cross, B Reville, G Gregori

Enhanced proton beam collimation in the ultra-intense short pulse regime


JS Green, NP Dover, M Borghesi, CM Brenner, FH Cameron, DC Carroll, PS Foster, P Gallegos, G Gregori, P McKenna, CD Murphy, Z Najmudin, CAJ Palmer, R Prasad, L Romagnani, KE Quinn, J Schreiber, MJV Streeter, S Ter-Avetisyan, O Tresca, M Zepf, D Neely

Quantum theory of Thomson scattering


BJB Crowley, G Gregori

Observations of strong ion-ion correlations in dense plasmas

PHYSICS OF PLASMAS 21 (2014) ARTN 056302

T Ma, L Fletcher, A Pak, DA Chapman, RW Falcone, C Fortmann, E Galtier, DO Gericke, G Gregori, J Hastings, OL Landen, S Le Pape, HJ Lee, B Nagler, P Neumayer, D Turnbull, J Vorberger, TG White, K Wuensch, U Zastrau, SH Glenzer, T Doeppner

Observations of continuum depression in warm dense matter with x-ray Thomson scattering.

Physical review letters 112 (2014) 145004-

LB Fletcher, AL Kritcher, A Pak, T Ma, T Döppner, C Fortmann, L Divol, OS Jones, OL Landen, HA Scott, J Vorberger, DA Chapman, DO Gericke, BA Mattern, GT Seidler, G Gregori, RW Falcone, SH Glenzer

Detailed measurements of the electron densities, temperatures, and ionization states of compressed CH shells approaching pressures of 50 Mbar are achieved with spectrally resolved x-ray scattering. Laser-produced 9 keV x-rays probe the plasma during the transient state of three-shock coalescence. High signal-to-noise x-ray scattering spectra show direct evidence of continuum depression in highly degenerate warm dense matter states with electron densities ne>1024  cm-3. The measured densities and temperatures agree well with radiation-hydrodynamic modeling when accounting for continuum lowering in calculations that employ detailed configuration accounting.

Turbulent amplification of magnetic fields in laboratory laser-produced shock waves

NATURE PHYSICS 10 (2014) 520-524

J Meinecke, HW Doyle, F Miniati, AR Bell, R Bingham, R Crowston, RP Drake, M Fatenejad, M Koenig, Y Kuramitsu, CC Kuranz, DQ Lamb, D Lee, MJ MacDonald, CD Murphy, H-S Park, A Pelka, A Ravasio, Y Sakawa, AA Schekochihin, A Scopatz, P Tzeferacos, WC Wan, NC Woolsey, R Yurchak, B Reville, G Gregori

Electron-ion equilibration in ultrafast heated graphite.

Physical review letters 112 (2014) 145005-

TG White, NJ Hartley, B Borm, BJ Crowley, JW Harris, DC Hochhaus, T Kaempfer, K Li, P Neumayer, LK Pattison, F Pfeifer, S Richardson, AP Robinson, I Uschmann, G Gregori

We have employed fast electrons produced by intense laser illumination to isochorically heat thermal electrons in solid density carbon to temperatures of ∼10,000  K. Using time-resolved x-ray diffraction, the temperature evolution of the lattice ions is obtained through the Debye-Waller effect, and this directly relates to the electron-ion equilibration rate. This is shown to be considerably lower than predicted from ideal plasma models. We attribute this to strong ion coupling screening the electron-ion interaction.

Evidence for a glassy state in strongly driven carbon.

Scientific reports 4 (2014) 5214-

CR Brown, DO Gericke, M Cammarata, BI Cho, T Döppner, K Engelhorn, E Förster, C Fortmann, D Fritz, E Galtier, SH Glenzer, M Harmand, P Heimann, NL Kugland, DQ Lamb, HJ Lee, RW Lee, H Lemke, M Makita, A Moinard, CD Murphy, B Nagler, P Neumayer, KU Plagemann, R Redmer, D Riley, FB Rosmej, P Sperling, S Toleikis, SM Vinko, J Vorberger, S White, TG White, K Wünsch, U Zastrau, D Zhu, T Tschentscher, G Gregori

Here, we report results of an experiment creating a transient, highly correlated carbon state using a combination of optical and x-ray lasers. Scattered x-rays reveal a highly ordered state with an electrostatic energy significantly exceeding the thermal energy of the ions. Strong Coulomb forces are predicted to induce nucleation into a crystalline ion structure within a few picoseconds. However, we observe no evidence of such phase transition after several tens of picoseconds but strong indications for an over-correlated fluid state. The experiment suggests a much slower nucleation and points to an intermediate glassy state where the ions are frozen close to their original positions in the fluid.

Resolving ultrafast heating of dense cryogenic hydrogen.

Physical review letters 112 (2014) 105002-

U Zastrau, P Sperling, M Harmand, A Becker, T Bornath, R Bredow, S Dziarzhytski, T Fennel, LB Fletcher, E Förster, S Göde, G Gregori, V Hilbert, D Hochhaus, 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, T Döppner, SH Glenzer, R Redmer

We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a ≲300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of ∼0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.

Electron-phonon equilibration in laser-heated gold films

PHYSICAL REVIEW B 90 (2014) ARTN 014305

TG White, P Mabey, DO Gericke, NJ Hartley, HW Doyle, D McGonegle, DS Rackstraw, A Higginbotham, G Gregori

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

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.

Nanosecond Imaging of Shock- and Jet-Like Features


ER Tubman, R Crowston, R Alraddadi, HW Doyle, J Meinecke, JE Cross, R Bolis, D Lamb, P Tzeferacos, D Doria, B Reville, H Ahmed, M Borghesi, G Gregori, NC Woolsey

Probing the complex ion structure in liquid carbon at 100 GPa

Physical Review Letters 111 (2013)

D Kraus, J Vorberger, DO Gericke, V Bagnoud, A Blažević, W Cayzac, AC Frank, G Gregori, A Ortner, A Otten, F Roth, G Schaumann, D Schumacher, K Siegenthaler, FR Wagner, K Wünsch, M Roth

We present the first direct experimental test of the complex ion structure in liquid carbon at pressures around 100 GPa, using spectrally resolved x-ray scattering from shock-compressed graphite samples. Our results confirm the structure predicted by ab initio quantum simulations and demonstrate the importance of chemical bonds at extreme conditions similar to those found in the interiors of giant planets. The evidence presented here thus provides a firmer ground for modeling the evolution and current structure of carbon-bearing icy giants like Neptune, Uranus, and a number of extrasolar planets. © 2013 American Physical Society.

Laboratory experiments on plasma jets in a magnetic field using high-power lasers

EPJ Web of Conferences 59 (2013)

K Nishio, Y Sakawa, Y Kuramitsu, T Morita, T Ide, M Kuwada, M Koga, T Kato, T Norimatsu, CD Grégory, NC Woolsey, CD Murphy, G Gregori, K Schaar, A Dizière, M Kœnig, A Pelka, S Wang, Q Dong, YT Li, H Takabe

The experiments to simulate astrophysical jet generation are performed using Gekko XII (GXII) HIPER laser system at the Institute of Laser Engineering. In the experiments a fast plasma flow generated by shooting a CH plane (10 μm thickness) is observed at the rear side of the plane. By separating the focal spot of the main beams, a non-uniform plasma is generated. The non-uniform plasma flow in an external magnetic field (0.2∼0.3 T) perpendicular to the plasma is more collimated than that without the external magnetic field. The plasma β, the ratio between the plasma and magnetic pressure, is ≠1, and the magnetic Reynolds number is ∼150 in the collimated plasma. It is considered that the magnetic field is distorted by the plasma flow and enhances the jet collimation. © Owned by the authors, published by EDP Sciences, 2013.

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

High Energy Density Physics 9 (2013) 75-81

AM Scopatz, M Fatenejad, N Flocke, G Gregori, M Kœnig, DQ Lamb, DM 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.