Publications by Gianluca Gregori
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.
PHYSICS OF PLASMAS 22 (2015) ARTN 056311
NEW JOURNAL OF PHYSICS 17 (2015) ARTN 083051
Developed turbulence and nonlinear amplification of magnetic fields in laboratory and astrophysical plasmas.
Proceedings of the National Academy of Sciences of the United States of America 112 (2015) 8211-8215
The visible matter in the universe is turbulent and magnetized. Turbulence in galaxy clusters is produced by mergers and by jets of the central galaxies and believed responsible for the amplification of magnetic fields. We report on experiments looking at the collision of two laser-produced plasma clouds, mimicking, in the laboratory, a cluster merger event. By measuring the spectrum of the density fluctuations, we infer developed, Kolmogorov-like turbulence. From spectral line broadening, we estimate a level of turbulence consistent with turbulent heating balancing radiative cooling, as it likely does in galaxy clusters. We show that the magnetic field is amplified by turbulent motions, reaching a nonlinear regime that is a precursor to turbulent dynamo. Thus, our experiment provides a promising platform for understanding the structure of turbulence and the amplification of magnetic fields in the universe.
HIGH ENERGY DENSITY PHYSICS 17 (2015) 24-31
PHYSICS OF PLASMAS 22 (2015) ARTN 056307
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS 48 (2015) ARTN 224004
Observation of magnetic field generation via the Weibel instability in interpenetrating plasma flows
NATURE PHYSICS 11 (2015) 173-176
Laboratory measurements of resistivity in warm dense plasmas relevant to the microphysics of brown dwarfs.
Nature communications 6 (2015) 8742-
Since the observation of the first brown dwarf in 1995, numerous studies have led to a better understanding of the structures of these objects. Here we present a method for studying material resistivity in warm dense plasmas in the laboratory, which we relate to the microphysics of brown dwarfs through viscosity and electron collisions. Here we use X-ray polarimetry to determine the resistivity of a sulphur-doped plastic target heated to Brown Dwarf conditions by an ultra-intense laser. The resistivity is determined by matching the plasma physics model to the atomic physics calculations of the measured large, positive, polarization. The inferred resistivity is larger than predicted using standard resistivity models, suggesting that these commonly used models will not adequately describe the resistivity of warm dense plasma related to the viscosity of brown dwarfs.
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
HIGH ENERGY DENSITY PHYSICS 14 (2015) 1-5
JOURNAL OF INSTRUMENTATION 10 (2015) ARTN P04010
PLASMA PHYSICS AND CONTROLLED FUSION 56 (2014) ARTN 084001
PHYSICAL REVIEW E 90 (2014) ARTN 013104
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.
NATURE PHYSICS 10 (2014) 520-524
IEEE TRANSACTIONS ON PLASMA SCIENCE 42 (2014) 2496-2497