Publications by Gianluca Gregori


Observation of finite-wavelength screening in high-energy-density matter.

Nature communications 6 (2015) 6839-

DA Chapman, J Vorberger, LB Fletcher, RA Baggott, L Divol, T Döppner, RW Falcone, SH Glenzer, G Gregori, TM Guymer, AL Kritcher, OL Landen, T Ma, AE Pak, DO Gericke

A key component for the description of charged particle systems is the screening of the Coulomb interaction between charge carriers. First investigated in the 1920s by Debye and Hückel for electrolytes, charge screening is important for determining the structural and transport properties of matter as diverse as astrophysical and laboratory plasmas, nuclear matter such as quark-gluon plasmas, electrons in solids, planetary cores and charged macromolecules. For systems with negligible dynamics, screening is still mostly described using a Debye-Hückel-type approach. Here, we report the novel observation of a significant departure from the Debye-Hückel-type model in high-energy-density matter by probing laser-driven, shock-compressed plastic with high-energy X-rays. We use spectrally resolved X-ray scattering in a geometry that enables direct investigation of the screening cloud, and demonstrate that the observed elastic scattering amplitude is only well described within a more general approach.


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

High Energy Density Physics 14 (2015) 38-43

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


Ultrabright X-ray laser scattering for dynamic warm dense matter physics

NATURE PHOTONICS 9 (2015) 274-279

LB Fletcher, HJ Lee, T Doeppner, E Galtier, B Nagler, P Heimann, C Fortmann, S LePape, T Ma, M Millot, A Pak, D Turnbull, DA Chapman, DO Gericke, J Vorberger, T White, G Gregori, M Wei, B Barbrel, RW Falcone, C-C Kao, H Nuhn, J Welch, U Zastrau, P Neumayer, JB Hastings, SH Glenzer


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, P Belancourt, DA Chapman, T Doeppner, RP Drake, DO Gericke, SH Glenzer, D Khaghani, S LePape, T Ma, P Neumayer, A Pak, L Peters, S Richardson, J Vorberger, TG White, G Gregori


SCALING OF MAGNETO-QUANTUM-RADIATIVE HYDRODYNAMIC EQUATIONS: FROM LASER-PRODUCED PLASMAS TO ASTROPHYSICS

ASTROPHYSICAL JOURNAL 795 (2014) ARTN 59

JE Cross, B Reville, G Gregori


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

PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 084001

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


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.


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.


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


Nanosecond Imaging of Shock- and Jet-Like Features

IEEE TRANSACTIONS ON PLASMA SCIENCE 42 (2014) 2496-2497

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


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


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


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.


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.


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


Quantum theory of Thomson scattering

HIGH ENERGY DENSITY PHYSICS 13 (2014)

BJB Crowley, G Gregori


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.


Modeling HEDLA magnetic field generation experiments on laser facilities

High Energy Density Physics 9 (2013) 172-177

M Fatenejad, AR Bell, A Benuzzi-Mounaix, R Crowston, PP Drake, N Flocke, G Gregori, M Kœnig, CM Krauland, DQ Lamb, D Lee, JR Marquès, J Meinecke, F Miniati, CD Murphy, H Park, A Pelka, A Ravasio, BA Remington, B Reville, AM Scopatz, P Tzeferacos, K Weide, NC Woolsey, RP Young, R Yurchak

The Flash Center is engaged in a collaboration to simulate laser driven experiments aimed at understanding the generation and amplification of cosmological magnetic fields using the FLASH code. In these experiments a laser illuminates a solid plastic or graphite target launching an asymmetric blast wave into a chamber which contains either Helium or Argon at millibar pressures. Induction coils placed several centimeters away from the target detect large scale magnetic fields on the order of tens to hundreds of Gauss. The time dependence of the magnetic field is consistent with generation via the Biermann battery mechanism near the blast wave. Attempts to perform simulations of these experiments using the FLASH code have uncovered previously unreported numerical difficulties in modeling the Biermann battery mechanism near shock waves which can lead to the production of large non-physical magnetic fields. We report on these difficulties and offer a potential solution. © 2012 Elsevier B.V.