Journal
HIGH ENERGY DENSITY PHYSICS
Volume 8, Issue 1, Pages 38-45Publisher
ELSEVIER
DOI: 10.1016/j.hedp.2011.11.001
Keywords
Astrophysical Collisionless shocks; Weibel instability; Electromagnetic instabilities; Interpenetrating plasmas; Thomson scattering
Categories
Funding
- Lawrence Livermore National Security, LLC, (LLNS) [DE-AC52-07NA27344]
- European Research Council under the European Community [256973, 247039]
- RTRA Triangle de la physique
- Institut Laser Plasma
- European Research Council (ERC) [256973] Funding Source: European Research Council (ERC)
- Direct For Mathematical & Physical Scien
- Division Of Astronomical Sciences [0909167] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [0807381] Funding Source: National Science Foundation
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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 highspeed plasma flows resulting from laser ablation of solid targets using similar to 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. Published by Elsevier Ltd.
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