Particle- in- cell simulations of plasma heating inside a density scale length for the interaction of ultra-short laser pulse with under-dense plasma

In this paper, nonlinear mechanisms of electron heating during the earlier stage of the interaction of an ultra-intense short laser pulse () with an under-dense plasma () inside a preformed density scale length has been investigated for exponential density profile. The fully kinetic particle in cell simulation code (1D3V) has been made to study the plasma heating at onset time of interaction. Our simulations indicate that, for ultra-intense short laser pulse, the nonlinear pulse scatterings are found to be very fast at the earlier time of interaction and cause plasma heating. As a key point in our discussion, our parametric simulations show that at the very earlier stage of interaction, two main electrostatic mechanisms, vacuum-plasma wave break together with longitudinal plasma oscillations, are the dominant acceleration mechanisms which lead to electron chaotic pattern and plasma heating. Meanwhile, studying the effect of density scale lengths on plasma heating revealed that, for exponential density profile, main acceleration mechanisms mentioned above are sufficiently developed during the propagation in typical short density scale lengths about for normalized vector potential .