The cosmic-ray-driven non-resonant instability of Bell (2004) assumes that both the cosmic rays and the background plasma are collisionless. It is a special case of non-resonant instabilities that are active across a range of collisionalities. In laser-plasmas they manifest themselves as heat flow instabilities and instabilities driven by currents of energetic electrons (Bell, Kingham,...
We recently proposed that cosmic rays between the knee and ankle can be produced in young compact stellar clusters. This relies on the efficient production of turbulent magnetic fields in the cluster core, and a fast shock launched from the explosion of a massive star. Some preliminary numerical simulations to expl0re these ideas will be presented. Laboratory experiments using high-power...
Pulsars are neutron stars that emit coherent radio beams out of their magnetic poles. However, the origin and exact mechanism of their coherent radio emission are still under investigation. We exploited plasma bunches, clouds of electron-positron pairs, created during spark events in gap regions by utilizing particle-in-cell simulations streaming instabilities and hot bunches to study the...
I will start with a brief introduction summarizing my view of what has already been learnt about particle acceleration in both astrophysical settings and in laser-plasma interactions using the test-particle approach. I will then present some recent results on test-particle acceleration at relativistic shock fronts using both analytical and Monte-Carlo techniques [1,2,3]. Contrary to previous...
When applied to compute the density jump of a shock, the standard magnetohydrodynamic (MHD) formalism assumes that all the upstream material passes downstream, together with the momentum and energy it carries, and that pressures are isotropic. In a collisionless shock, shock-accelerated particles going back and forth around the front can invalidate the first assumption. In addition, an...
Astrophysical shock waves are among the most powerful particle accelerators in the Universe. Generated by violent interactions of supersonic plasma flows with the interstellar or intergalactic medium, shocks are inferred to heat the plasma, amplify magnetic fields, and accelerate electrons and protons to highly relativistic speeds. However, the exact mechanisms that control magnetic field...
Transport processes are virtually ubiquitous in engineering fluid and plasma problems but their properties are not always well-determined, particularly when complex microphysics is at play. One outstanding example is heat flux, which according to both laser plasma experiments performed at NIF and more recently measurements of astrophysical plasmas becomes strongly suppressed with respect to...
