Shock creation and particle acceleration driven by plasma expansion into a rarefied medium

The expansion of a dense plasma through a more rarefied ionised medium is a phenomenon of interest in various physics environments ranging from astrophysics to high energy density laser- matter laboratory experiments. Here this situation is modeled via a 1D Particle-In-Cell simulation; a jump in the plasma density of a factor of 100 is introduced in the middle of an otherwise equally dense electron-proton plasma with an uniform proton and electron temperature of 10eV and 1keV respectively. The diffusion of the dense plasma, through the rarified one, triggers the onset of different nonlinear phenomena such as a strong ion-acoustic shock wave and a rarefaction wave. Secondary structures are detected, some of which are driven by a drift instability of the rarefaction wave. Efficient proton acceleration occurs ahead of the shock, bringing the maximum proton velocity up to 60 times the initial ion thermal speed

Conditions for the onset of the current filamentation instability in the laboratory

Current Filamentation Instability (CFI) is capable of generating strong magnetic fields relevant to explain radiation processes in astrophysical objects and lead to the onset of particle acceleration in collisionless shocks. Probing such extreme scenarios in the laboratory is still an open challenge. In this work, we investigate the possibility of using neutral $e^{-}$ $e^{+}$ beams to explore the CFI with realistic parameters, by performing 2D particle-in-cell simulations. We show that CFI can occur unless the rate at which the beam expands due to finite beam emittance is larger than the CFI growth rate and as long as the role of competing electrostatic two-stream instability (TSI) is negligible. We also show that the longitudinal energy spread, typical of plasma based accelerated electron-positron fireball beams, plays a minor role in the growth of CFI in these scenarios

Shocks in unmagnetized plasma with a shear flow: Stability and magnetic field generation

A pair of curved shocks in a collisionless plasma is examined with a two-dimensional particle-in-cell (PIC) simulation. The shocks are created by the collision of two electron-ion clouds at a speed that exceeds everywhere the threshold speed for shock formation. A variation of the collision speed along the initially planar collision boundary, which is comparable to the ion acoustic speed, yields a curvature of the shock that increases with time. The spatially varying Mach number of the shocks results in a variation of the downstream density in the direction along the shock boundary. This variation is eventually equilibrated by the thermal diffusion of ions. The pair of shocks is stable for tens of inverse ion plasma frequencies. The angle between the mean flow velocity vector of the inflowing upstream plasma and the shock's electrostatic field increases steadily during this time. The disalignment of both vectors gives rise to a rotational electron flow, which yields the growth of magnetic field patches that are coherent over tens of electron skin depths.Comment: 10 pages, 10 figures accepted for publication in Physics of Plasma

The cross-border project between France and Italy MARS+. Sub-project - Innovative technologies for the mechanization of the areas hard to reach

The care and protection of the mountain areas and their traditional crops were some of the reasons that led regional governments of Liguria and Tuscany to participate in the strategic project “Sea, Countryside and Land: potentiate the strategic unitarily” (MARS +). This project has also involved the participation of the four cross-border regions: Tuscany (leader), Sardinia, Liguria and Corsica. The aim was to promote the development of the innovations and entrepreneurship in the rural areas in order to increase competitiveness. In particular, the subproject SC has provided the transfer of innovations to facilitate the processes of mechanization in vineyards and olive orchards in contexts defined as “heroic”, areas of high landscape and environmental value in which the typical cultures has been always carried out, generally, on terraces or slopes. These conditions require a great effort by the farmers and result in high production costs. The transfer of the innovations has provided the organization of demonstration days in which the technological solutions for the management of the farming operations in vineyards and olive orchards were proposed and tested. During these events, the participative process was fundamentally reconfirmed, not only as a means to expand the knowledge of innovative products, but also as an opportunity for farmers, retailers, manufacturers, researchers, and local administrators to interact and facilitate the development of other technologies. The parameters that led to the innovative solutions included: the small size, user-friendliness, agility, and the ability of operating on systems not easily accessible. These products must also ensure the ergonomics and safety of workers performing all the growing operations. A thorough research of the available technologies and prototypes, still under development, affirms the presence of many innovations. These innovations not only allow the execution of all the field operations in the vineyard and olive orchards and significant time and cost reduction but also ensure the performance in complete safety. This research has shown the constant development of these products and how the use of electronics and mechatronics is becoming more prevalent

One-dimensional thermal pressure-driven expansion of a pair cloud into an electron-proton plasma

Recently a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell (PIC) simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons.Comment: 5 pages 4 figures, accepted for publication in Physics of Plasma