High density plasma instabilities in intense laser irradiation

Recent experimental results on the filamentation of laser accelerated proton beams at high laser irradiation intensities are compared to particle-in-cell simulations. In simulations, several qualitatively different mechanisms of filamentation of electrons can be observed. Depending on the specific laser and target parameters such as flatness or density, the relative role of individual electron instabilities can be actively controlled. It is demonstrated how filamentation of electron currents going into the target and heating the rear surface can translate into ion filamentation which consequently exhibit strong correlation with the front side laser-electron instability physics. The impact on ion energy scaling are discussed. Experimental observation of proton filamentation can thus be a valuable diagnostics of the laser-electron interaction at the foil front surface. We moreover propose and discuss other more direct techniques for probing spatio-temporal electron density and ionization.