Fast electron transport in solid targets

Abstract

The generation of fast electrons in high intensity laser-solid interactions has been extensively studied eg [1,2]. A frequently used diagnostic for fast electrons is Kα emission from layered targets, the interpretation of such data requires a model for the transport of the fast electrons through the target [3]. Such experiments have largely been interpreted using models including only collisional effects. However recent works have shown that at high intensities electric and magnetic fields could be important [4–6]. Here we present a code which can deal with the transport of fast electrons through solid targets including both collisions and field generation. The fast electrons are represented by a relativistic Fokker-Planck equation including drag, angular scattering, electric and magnetic fields, which is solved using stochastic differential equations (SDEs). The background is represented by E=ηjb, where η is the resistivity and jb the background current density. Changes in resistivity due to heating of the background by the fast electrons are included. Current balance is assumed allowing the electric field to be found directly from the fast electron current. Rotational symmetry is assumed. The treatment is valid for fast electron number densities much less than that of the background, fast electron energies much greater than the background temperature and time scales short enough that magnetic diffusion and thermal conduction are negligible. The neglect of ionization also limits the validity of the model.