Seminar by Laurent Gremillet

The physics of collisionless shocks in laser-driven plasma interactions

Laurent Gremillet, CEA (Commissariat à l'énergie atomique), France, will give a seminar on the physics of collisionless shocks in laser-driven plasma interactions.


Collisionless turbulent shocks are attracting much attention due to their potential as efficient sources of cosmic rays and nonthermal radiation in high-energy astrophysical systems. First-principles kinetic simulations have revealed that such structures obey a self-regulation process whereby the energized particles reflected upstream continuously excite micro-instabilities, thus sustaining the electromagnetic turbulence that dissipates the incoming flow energy. Recently, much experimental effort has gone into producing laser-driven plasma collisions prone to the ion-Weibel instability, which mediates shock formation with no external magnetic field. Although the development of magnetized ion filaments has been clearly evidenced, all of the experiments conducted so far fell short of creating a fully-formed, propagating shock.
Advances in this novel field of laboratory astrophysics necessitate further understanding of the instability regimes accessible on available laser systems. For instance, achieving truly collisionless conditions severely constrains the properties of the interacting plasmas. Also, computational limitations force the use of simplifications in kinetic simulations −most notably reduced ion-to-electron mass ratios−, and hence the precise plasma conditions and dynamics leading to shock formation were poorly known until recently, especially in a parameter range of experimental interest.
This presentation, based on large-scale kinetic simulations, aims to provide increased insight into this problem. First, we will discuss the different stages of the instability and show that shock generation implies a minimum of ∼ 2 × 100 kJ laser drive energy. Second, we will explore the effects of Coulomb collisions on the Weibel instability occurring in experimentally relevant, multi-ion plasma flows.
Category Seminar
Location: N6115, seminar room, Fysik Origo, Fysik
Starts: 14 November, 2017, 13:30
Ends: 14 November, 2017, 14:30

Published: Mon 13 Nov 2017.