New Perspectives in Laboratory Astrophysics Using High Intensity Lasers
Dr. Emmanuel d'Humieres, University of Bordeaux, France
March 29, 2016, 11:00am - 12:00pm, EBUII 479
Abstract: The development of high intensity laser facilities has allowed making tremendous progress in laser electron acceleration, laser ion acceleration and high-energy radiation generation. A new trend is to use these facilities for laboratory astrophysics studies in order to explore regimes that cannot be reached on high-energy long pulse duration facilities.
In this presentation, several examples of recent laboratory astrophysics studies using high intensity lasers will be reviewed. First, two studies both experimental and theoretical on magnetized plasmas generated by high intensity (> 1018 W/cm2) lasers will be presented. The coupling of terawatt-class lasers along with efficient magnetic pulsers now allows to study physics related to collisionless shocks in supernovae remnants (SNRs), at the stage of the interaction with an ambient magnetized interstellar medium . Such studies aim to give a deeper understanding of the formation of magnetized collisionless shocks and their structure, interaction of a plasma flow with the magnetized medium, including collisionless magnetization, particle acceleration and energy redistribution. Results of experiments performed using the JLF/Titan laser facility where two laser-produced TNSA plasmas were made to collide in an ambient magnetic field, will be discussed. In order to reach even higher magnetic fields, we have shown that by adjusting target geometry and laser pulse parameters it is possible to generate spontaneous high amplitude (Gigagauss) magnetic fields which possess confined spatial structure and exist much longer than the pulse duration time . The latter becomes possible when the magnetic field becomes frozen in the generated laser plasma. Then the resulting magnetized plasma structures are expanding on a time scale of hydrodynamic processes, which may exceed the scale of several tens of picoseconds and more. A first experiment using a snail geometry has recently been performed on LFEX, in Japan.
We have also prepared two types of experiments on forthcoming ultra high intensity (> 1022 W/cm2) laser facilities, like Apollon and ELI being built in Europe. Direct production of electron-positron pairs in photon collisions is one of the basic processes in the Universe. The linear Breit-Wheeler (BW) pair creation process (g+g to e++e-), is the lowest threshold process in photon-photon interaction, controlling the energy release in Gamma Ray Bursts and Active Galactic Nuclei. It is also responsible for the TeV cutoff in the photon energy spectrum of extra-galactic sources. The linear BW process has never been clearly observed in laboratory with important probability of matter creation. Using MeV photon sources a new experimental set-up based on numerical simulations with QED effects is proposed to achieve more than 104 BW pairs per shot . Finally, we have also assessed the capability of exawatt lasers to generate relativistic pair plasmas prone to collective phenomena of astrophysical interest. In particular, we have shown that the Weibel-unstable collision between two laser-driven pair jets leads to an ultra-fast, synchrotron-enhanced thermalization, up to a stage close to shock formation .
References:  Higginson D., et al. High Energy Density Physics, doi:10.1016/j.hedp.2014.11.007 (2014).  Korneev P., et.al., Phys. Rev. E 91, 043107 (2015),  Ribeyre, X., et al., Phys. Rev. E, 93, 013201 (2016),  Lobet M., et al., Phys. Rev. Lett. 115, 215003 (2015).
Bio: After a PhD on ion acceleration by laser plasma interaction at CEA in France, Emmanuel d'Humières was a postdoc at the University of Nevada, Reno (UNR) and at Ecole Polytechnique working on charged particles transport in plasmas. He is now associate professor at the University of Bordeaux, where he is in charge of international mobility for the Physics Department and of the Fusion Science Master. At the CELIA laboratory, he works on particle acceleration and radiation generation using intense lasers and on the associated simulation codes. He is also a member of the Institut Universitaire de France since 2014.