Skip to main content
Home
Department Of Physics text logo
  • Research
    • Our research
    • Our research groups
    • Our research in action
    • Research funding support
    • Summer internships for undergraduates
  • Study
    • Undergraduates
    • Postgraduates
  • Engage
    • For alumni
    • For business
    • For schools
    • For the public
Menu
Space and Planets (artistic image)
Credit: hdwallpaperim.com/

Gianluca Gregori

Professor of Physics

Research theme

  • Lasers and high energy density science
  • Plasma physics

Sub department

  • Atomic and Laser Physics

Research groups

  • Laboratory astroparticle physics
  • Oxford Centre for High Energy Density Science (OxCHEDS)
Gianluca.Gregori@physics.ox.ac.uk
Telephone: 01865 (2)82639
Clarendon Laboratory, room 029.8
  • About
  • Publications

Studying astrophysical collisionless shocks with counterstreaming plasmas from high power lasers

High Energy Density Physics 8:1 (2012) 38-45

Authors:

HS Park, DD Ryutov, JS Ross, NL Kugland, SH Glenzer, C Plechaty, SM Pollaine, BA Remington, A Spitkovsky, L Gargate, G Gregori, A Bell, C Murphy, Y Sakawa, Y Kuramitsu, T Morita, H Takabe, DH Froula, G Fiksel, F Miniati, M Koenig, A Ravasio, A Pelka, E Liang, N Woolsey, CC Kuranz, RP Drake, MJ Grosskopf

Abstract:

Collisions of high Mach number flows occur frequently in astrophysics, and the resulting shock waves are responsible for the properties of many astrophysical phenomena, such as supernova remnants, Gamma Ray Bursts and jets from Active Galactic Nuclei. Because of the low density of astrophysical plasmas, the mean free path due to Coulomb collisions is typically very large. Therefore, most shock waves in astrophysics are "collisionless", since they form due to plasma instabilities and self-generated magnetic fields. Laboratory experiments at the laser facilities can achieve the conditions necessary for the formation of collisionless shocks, and will provide a unique avenue for studying the nonlinear physics of collisionless shock waves. We are performing a series of experiments at the Omega and Omega-EP lasers, in Rochester, NY, with the goal of generating collisionless shock conditions by the collision of two high-speed plasma flows resulting from laser ablation of solid targets using ∼10 16 W/cm 2 laser irradiation. The experiments will aim to answer several questions of relevance to collisionless shock physics: the importance of the electromagnetic filamentation (Weibel) instabilities in shock formation, the self-generation of magnetic fields in shocks, the influence of external magnetic fields on shock formation, and the signatures of particle acceleration in shocks. Our first experiments using Thomson scattering diagnostics studied the plasma state from a single foil and from double foils whose flows collide "head-on" Our data showed that the flow velocity and electron density were 10 8 cm/s and 10 19 cm -3, respectively, where the Coulomb mean free path is much larger than the size of the interaction region. Simulations of our experimental conditions show that weak Weibel mediated current filamentation and magnetic field generation were likely starting to occur. This paper presents the results from these first Omega experiments. © 2011.
More details from the publisher

X-ray Thomson scattering on shocked graphite

High Energy Density Physics 8:1 (2012) 46-49

Authors:

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

Abstract:

We present measurements of the changes in the microscopic structure of graphite in a laser-driven shock experiment with X-ray scattering. Laser radiation with intensities of ∼2 × 10 13 W/cm 2 compressed the carbon samples by a factor of two reaching pressures of ∼90 GPa. Due to the change of the crystalline structure the scattered signals of the probe radiation were modified significantly in intensity and spectral composition compared to the scattering on cold samples. It is shown that the elastic scattering on tightly bound electrons increases strongly due to the phase transition whereas the inelastic scattering on weakly bound electrons remains nearly unchanged for the chosen geometry. © 2011 Elsevier B.V.
More details from the publisher
More details

XUV spectroscopic characterization of warm dense aluminum plasmas generated by the free-electron-laser FLASH

Laser and Particle Beams 30:1 (2012) 45-56

Authors:

U Zastrau, T Burian, J Chalupsky, T Döppner, TWJ Dzelzainis, RR Fäustlin, C Fortmann, E Galtier, SH Glenzer, G Gregori, L Juha, HJ Lee, RW Lee, CLS Lewis, N Medvedev, B Nagler, AJ Nelson, D Riley, FB Rosmej, S Toleikis, T Tschentscher, I Uschmann, SM Vinko, JS Wark, T Whitcher, E Förster

Abstract:

We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 μJ are focused to intensities ranging between 10 13 and 10 17 W/cm 2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations. © 2012 Cambridge University Press.
More details from the publisher
More details

Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves

Nature 481:7382 (2012) 480-483

Authors:

G Gregori, A Ravasio, CD Murphy, K Schaar, A Baird, AR Bell, A Benuzzi-Mounaix, R Bingham, C Constantin, RP Drake, M Edwards, ET Everson, CD Gregory, Y Kuramitsu, W Lau, J Mithen, C Niemann, HS Park, BA Remington, B Reville, APL Robinson, DD Ryutov, Y Sakawa, S Yang, NC Woolsey, M Koenig, F Miniati

Abstract:

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10 -21 gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution. © 2012 Macmillan Publishers Limited. All rights reserved.
More details from the publisher

Generation of scaled protogalactic seed magnetic fields in laser-produced shock waves.

Nature 481:7382 (2012) 480-483

Authors:

G Gregori, A Ravasio, CD Murphy, K Schaar, A Baird, AR Bell, A Benuzzi-Mounaix, R Bingham, C Constantin, RP Drake, M Edwards, ET Everson, CD Gregory, Y Kuramitsu, W Lau, J Mithen, C Niemann, H-S Park, BA Remington, B Reville, APL Robinson, DD Ryutov, Y Sakawa, S Yang, NC Woolsey, M Koenig, F Miniati

Abstract:

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations. Although other mechanisms may also operate, currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about 10(-21) gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations, astrophysical environments can effectively be reproduced in the laboratory. Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields sufficiently to affect galaxy evolution.
More details from the publisher
More details
More details

Pagination

  • First page First
  • Previous page Prev
  • …
  • Page 46
  • Page 47
  • Page 48
  • Page 49
  • Current page 50
  • Page 51
  • Page 52
  • Page 53
  • Page 54
  • …
  • Next page Next
  • Last page Last

Footer Menu

  • Contact us
  • Giving to the Dept of Physics
  • Work with us
  • Media

User account menu

  • Log in

Follow us

FIND US

Clarendon Laboratory,

Parks Road,

Oxford,

OX1 3PU

CONTACT US

Tel: +44(0)1865272200

University of Oxfrod logo Department Of Physics text logo
IOP Juno Champion logo Athena Swan Silver Award logo

© University of Oxford - Department of Physics

Cookies | Privacy policy | Accessibility statement

Built by: Versantus

  • Home
  • Research
  • Study
  • Engage
  • Our people
  • News & Comment
  • Events
  • Our facilities & services
  • About us
  • Current students
  • Staff intranet