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...
Hot luminous massive stars usually have stellar winds. These winds are accelerated by light scattering or absorption on different particles. Not all particles are equally efficient in gaining momentum. For massive hot stars, the dominant accelerating mechanism is scattering in resonance spectral lines of elements heavier than hydrogen and helium. The momentum is distributed throughout the...
TBD
The long-term evolution of the orbit of a satellite black hole captured by a massive galactic nucleus has been examined. Repetitive transits across the accretion disk slab create a turbulent wake that needs to be further examined in order to estimate the effects of dragging and the amount of material pushed out of the disk plane.
Fast Radio Bursts (FRBs) are transient and fast (millisecond) episodes of very strong and coherent radio emission. The origin of FRBs is still unknown. In one case, the counterpart in X rays has been identified as a magnetar. We present a scenario where coherent emission is produced in the magnetosphere of a neutron star, when two different outflows from the magnetar interact: a...
The magnetic and radiative versions of the Penrose process of extraction of the rotation energy of a magnetized black hole are discussed and their astrophysical relevance is demonstrated. It is shown that realistic magnetized supermassive black holes with mass larger than 10^{9} Solar masses could accelerate protons up to energy 10^{22}eV, while the Srg A* black hole is able to accelerate...
Interaction of ultraintense lasers with matter results in $\gamma$-photon emission mainly via the multiphoton Compton scattering process, a phenomenon being of primary interest of the recently developed and upcoming multi-petawatt laser facilities. The $\gamma$-ray flashes have always been of interest for a wide portion of the scientific community, regardless if the research focuses on 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...
Astrophysically relevant super-critical quasi-perpendicular magnetized collisionless shocks can be produced and characterized in experiments using high power lasers irradiating solid targets, a background gas jet and a magnetic pulser. In this configuration the presence of both the external magnetic field and the background gas is crucial to observe the development of the collisionless shock...
Fast electron scattering on plasma ions due to stimulated Bremsstrahlung is investigated and modelled. Comparison with Coulomb scattering, at non-relativistic energies, suggests that stimulated Bremsstrahlung scattering can be dominant and observable in radiation-driven, low density, large scale astrophysical plasmas. The conditions are met in the flaring solar corona. The effect of the solar...
We investigate the effect of azimuthal and axial ambient magnetic fields on the structure and evolution of a magnetized blast wave. The blast wave is driven by a central source of energy and forms a shell that results from the accumulation of interstellar matter behind the shock front. A similarity form of the ambient magnetic field is assumed to obtain self-similar solutions. The model is...
We investigate the evolution of the separation between an adiabatic and a radiative shock. The contact discontinuity between the two gases is subject to the Rayleigh- Taylor and Richtmyer-Meshkov instability with radiative cooling. These dynamics will be studied experimentally for the first time in the optically thin regime using a laser-driven shock configuration. The shock will propagate in...
We carried out an experiment to generate photoionised plasma using line radiation. Using the high-power ns laser to irradiate the Ag-coated CH foil to produce an X-ray line source, which then photoionise Ar gas. Produced Ar-photoionised plasma achieved photoionisation parameter > 100 erg-cm s-1, the regime of interest of several astrophysical cases.
We demonstrate that the use of a keV X-ray...
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...
