Modeling the x-ray enhancement in foams for laser-driven soft x-ray sources

Abstract This paper investigates the mechanism that causes the x-ray enhancement in high-Z foams for laser-driven soft x-ray sources. By simulation of one-dimensional radiation-hydrodynamics, it is found that the x-ray enhancement is mainly due to the effect that, in foam target, shock wave compression significantly reduces the energy loss of hydrodynamic motion (kinetic energy). In solid target this effect is negligible for its low compressibility. Expressions of kinetic energy reduction (∆Ek=Ek,solid-Ek,foam) are given to model the improvement of laser-to-x-ray conversion efficiency. The ∆Ek given by the model agrees with the simulation result with about 15% error for foam density 0.07~0.3g/cc and for laser intensity 0.4×1015~2.0×1015W/cm2. The model indicates that the x-ray enhancement is more efficient with lower foam density and higher laser intensity, which is also presented by the simulation results.