Micro-Astro-Shocks – MACH

Microinstabilities, the development of turbulence and particle acceleration process in collisionless shocks are studied via analytical studies (resolution of dispersion relation and linear growth rate study), numerical analysis (non-linear developments, study of turbulence, acceleration of particles) in non-relativistic shocks (magnetospheric shocks, supernova shocks) to the ultra-relativistic case (gamma ray bursts, pulsar winds). Because of the large scale dynamics necessary to these studies several numerical tools are developed: a PIC code (small space and temporal scales: shock formation, instabilities), and MHD-hybrid (large space and temporal scales, acceleration of particle). The provision of these two codes is the main aim of this ANR project.

The development of the PIC code SMILEI advances nominally, the Cerenkov emission corrector is implemented and the moving injector is about to be implemented. At this point the two principal technical goals for this code will be achieved. The development of PIC-MHD code is almost completed, a relativistic version should be ready for December 2016, exactly at the date envisaged in the original ANR proposal.
Several analytical studies have been conducted at the same time in both non-relativistic and relativistic shocks regimes. The numerical studies of these aspects will be the object of the second part of the ANR.
Finally a set-up for an experiment with the LMJ resulting from our collaboration has been selected.

Once the both numerical tools will be finalized we will investigate the numerical extension of the different analytical studies undertaken in the first part of the ANR project. A special focus will be conducted on the problem of particle acceleration efficiency in mildly relativistic shocks. We will also conduct the experiment selected for a next LMJ shot and exploit the resulting data sets.

1. Marcowith A., A Bret, A Bykov, M E Dieckman, L O’C Drury, B Lembège, M Lemoine, G Morlino, G Murphy, G Pelletier, I Plotnikov, B. Reville, M Riquelme, L Sironi and A Stockem Novo (2016) The microphysics of collisionless shock waves Reports on Progress in Physics, 79 (2016) 046901, doi:10.1088/0034-4885/79/4/046901
2. M. Lobet, C. Ruyer, A. Debayle, E. d'Humières, M. Grech, M. Lemoine, L. Gremillet : Ultrafast synchrotron-enhanced thermalization of laser-driven colliding pair plasmas, PRL 115 215003 (2016)
3 . Ardaneh K. D.S. Cai, K-I. Nishikawa, and B. Lembège Collisionless Weibel shocks and electron acceleration in gamma-ray bursts ;The Astrophysical Journal, 811:57 (9pp), 2015.
4. M. Lemoine, O. Ramos, L. Gremillet : Corrugation of relativistic magnetized shock waves, ApJ 827, 44 (2016)
3. M. Lemoine : A corrugated termination shock in pulsar wind nebulae ?, J. Plasm. Phys. 82 635820401 (2016)
5. M. Lemoine : The synchrotron self-Compton spectrum of relativistic blast waves at large Y, MNRAS 453, 3772 (2015)
6. L. Sironi, U. Keshet, M. Lemoine : Relativistic shocks : particle acceleration and magnetization, Sp. Sc. Rev. 191, 519 (2015)
7. R. Zakine, M. Lemoine : The elusive synchrotron precursor of collisionless shocks, AA, submitted (2016)

The origin of highly relativistic particles and of the associated secondary radiation in energetic astrophysical sources, such as supernovae remnants, pulsars, micro-quasars, active galactic nuclei, gamma-ray bursts… represents one the key questions of present day astrophysics. It is generally accepted that particle acceleration and non-thermal radiation production are associated with the dissipation of energy in collisionless shock waves, be they sub-relativistic, mildly relativistic or even ultra-relativistic. Recent developments, both on the theoretical and on the experimental level have led to the conclusion that the acceleration of particles, the structure of the shock and the generation of turbulence form an interdependent triptych so that one needs to address physical processes that act from the microscopic plasma scales to the largest scales, a rather unusual situation in astrophysics. To achieve self-consistency, the model must furthermore integrate the non-linear couplings of these different scales. One thus needs to bring together knowledge from several disciplines – high-energy astrophysics, space plasma physics, laser plasma physics -- and to develop highly efficient numerical tools. This is precisely the aim of the present project MACH, which proposes to combine analytical studies with state of the art numerical simulations and plasma experiments in order to undertake a multi-scale self-consistent study of astrophysical shocks, of particle acceleration mechanisms and of radiation generation.

At the end of the project, we will deliver to the French community two state of the art numerical codes: a relativistic 3D Particle-in-Cell (PIC) code to perform fully self-consistent refined studies of shock physics and a hybrid relativistic PIC-MHD code that will address phenomena on larger spatial and temporal scales, by coupling a MHD treatment for the flow and the electromagnetic field structure with a PIC module for the non-thermal particle population. This project is obviously inter-disciplinary as it involves physicists from the above three disciplines. It combines their complementary visions with complementary methodological tools: numerical simulations, analytical guidance, plasma experiments of collisionless shock formation. Eventually, MACH will boost the French astrophysical community towards the forefront of research in a field that is currently led by American and Japanese teams.

The MACH project is organized in three parallel scientific tasks: (1) upgrade of existing PIC codes issued from the laser-plasma (2) develop PIC simulations for mildly-relativistic and relativistic collisionless shocks under the guidance of analytical studies. Set up the conditions for the laser-plasma experiments of collisionless shock physics; (3) development of a non-relativistic then relativistic hybrid PIC-MHD code in parallel with the execution of MHD simulations of astrophysical collisionless shock waves with adaptative mesh refinement, using the existing AMR-VAC code. We ask for the fundings of two post-doctoral fellows for 2 years and the half of a thesis as well as the budget for collaborative work and attendance to conferences and for small equipments.