Investigation of laser generated plasmas for astrophysical applications

Abstract

ES-Electron Screening is a key parameter for proper understanding of several astrophysical processes, from stellar evolution to spectacular events like supernova explosions. The aim of this work is try to reproduce in laboratory plasmas of astrophysical interest via the laser ablation technique for the study of fusions rates in plasmas to better understand the ES effects. While ES has an explicit dependence on the ratio between the electron density and the electron temperature, the fusion reaction rate depends both on the plasma density and from the ion temperature. In a laser irradiance regime of 10^10-10^12 W/cm2 the produced plasmas ion temperatures are on the order of 100eV à à à ¢ 300eV, high enough to ensure a not negligible number of fusion events, and at the same time, electron temperatures which are on the order of few eV s are low enough to provide to a strong influence of ES. This confers to LPP the unique peculiarity to be employed for fusion reaction rates measurements in a low energy domain. Moreover, this domain is up to now unexplored and could open new field of scientific interest in nuclear-astrophysics. In this energy regime also multiple interacting laser plasmas, can be employed for the same purposes. For example, two colliding plasmas generate, inside their interaction zone, a high rate collision particles layer, where they stagnate for several hundreds of nanosecond forming in this way a third plasma composed by cold electrons with electron temperatures on the order of few that can result very useful to study the ES. On these purposes, a new experimental apparatus at the LNS-INFN of Catania was built. The apparatus was constructed in order to realize measurements with single expanding and colliding plasmas. Most of the results obtained during the last three years concern the characterization, in terms of density, temperature and temporal dynamic, of single and double expanding plasma plumes. Single plasma expansion was investigated in vacuum and in a background gas; measurements realized in at high fluence on metal Al targets permitted us to observe other than the classical hydrodynamic expansion of the plasma, some non linear processes driven by the formation of Double or Multy-layers, leading to plasma multifragmentation and complicates its temporal dynamic. Such effect has been never profoundly investigated in a low-laser energy regime up to now. Plume dynamic was nearby studied with numerical simulations, by using the Anisimov model. By numerical improvements to the code it is able to well reproduce the experimental observed plume expansion. Plasma collision was realized at the DCU-Dublin City University. We observed and characterized other than colliding plasmas produced from thick Al targets also colliding plumes generated from thin Al foils of 2à à à à ¼m of thickness. In this case a peculiar plasma dynamic was observed: most of the plasma expands forward and a slow backward plasma dynamic is observed on the rear side of the foil. The peculiar characteristics of the back-plasma, composed mostly by neutral atoms and electrons could results useful to study ES.