Publications by Gianluca Gregori
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
NATURE PHOTONICS 9 (2015) 274-279
Evidence of locally enhanced target heating due to instabilities of counter-streaming fast electron beams
PHYSICS OF PLASMAS 22 (2015) ARTN 020701
Nature communications 6 (2015) 6839-
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.
HIGH ENERGY DENSITY PHYSICS 14 (2015) 1-5
Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows
NATURE PHYSICS 11 (2015) 173-176
PHYSICAL REVIEW E 90 (2014) ARTN 013104
IEEE TRANSACTIONS ON PLASMA SCIENCE 42 (2014) 2496-2497
NATURE PHYSICS 10 (2014) 520-524
PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 084001
Scientific reports 4 (2014) 5214-
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.
Physical review letters 112 (2014) 105002-
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.
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-
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.
Physical review letters 112 (2014) 145004-
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.
Physical review letters 112 (2014) 145005-
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.
PHYSICS OF PLASMAS 21 (2014) ARTN 056302
SCALING OF MAGNETO-QUANTUM-RADIATIVE HYDRODYNAMIC EQUATIONS: FROM LASER-PRODUCED PLASMAS TO ASTROPHYSICS
ASTROPHYSICAL JOURNAL 795 (2014) ARTN 59
Orbital-free density-functional theory simulations of the dynamic structure factor of warm dense aluminum
Physical Review Letters 111 (2013)
Here, we report orbital-free density-functional theory (OF DFT) molecular dynamics simulations of the dynamic ion structure factor of warm solid density aluminum at T=0.5 eV and T=5 eV. We validate the OF DFT method in the warm dense matter regime through comparison of the static and thermodynamic properties with the more complete Kohn-Sham DFT. This extension of OF DFT to dynamic properties indicates that previously used models based on classical molecular dynamics may be inadequate to capture fully the low frequency dynamics of the response function. © 2013 American Physical Society.