Study of hot electron propagation in cone-wire targets and foams

Summary form only given as follows. The interaction of short, high intensity laser pulses with matter produces bursts of high energy particles. The transport properties of relativistic electrons in dense matter and the evolution of electric and magnetic fields associated with the propagation is crucial in many applications. Scaling laws for the fast electrons produced during ultrahigh intensity interactions give electron temperatures K_BT_hot ~ U_pond ~ 1 MeV times (I²/10¹⁹ W cm^-2 mum²)^0.5, with up to 30% of the laser energy converted into these relativistic electrons. There is debate on the behavior of such large currents inside matter, and on the extent to which electromagnetic instabilities will be detrimental to their propagation. Here we are presenting experimental results and analysis of data obtained at RAL and LULI under different irradiation conditions and using different targets. The data were obtained using proton imaging techniques. We investigated cone-wire targets to study the guiding and collimation of electron beams and low density foams to study the effect of electromagnetic instabilities associated with hot electron propagation. The data show a complex evolution of electric and magnetic fields and formation of filamentary instabilities. The experimentally measured propagation velocities of the observed field structures indicate the possibility of current inhibition at relativistic velocities.