Study of the impact of small-scale plasma modulations and the size of the plasma on seeded soft x-ray laser homogeneity.

Abstract

In the present work, we have used the 2D AMR hydrodynamic code with radiation transport ARWEN to study the plasma homogeneity alteration on small scale (1-10 μm) that may arise from initial target defects or driving laser intensity modulations. These simulations show that target rugosity imprints strongly the plasma creating a complicated pattern of electronic density. In addition to this, we have done several simulations of plasmas of different size (from 20 μm to 2 mm height) to study the different stages of a seeded soft x-ray laser amplifier. We have observed that 2D hydrodinamic effects lower the gain in small plasmas. As the main pulse, which creates the population inversion, interacts with a fully developed plasma, we have implemented a ray-tracing subroutine for the laser energy deposition in order to treat correctly the refraction effects of the short pulse. Simulations show that these effects are not negligible in rugous targets. Finally, simulations of the behaviour of the seeded beam in the amplifying plasma have been done with the 3D ray-tracing (amplification in non-homogeneous media) code SHADOX, as a post-processor of ARWEN. Prior ray-tracing, gain calculation is done on the output of ARWEN using a simple 3-level atomic model.