Acceleration of the ultrathin plasma foils by the laser radiation pressure promises a compact alternative of conventional accelerator delivering energetic ions. It was shown, that a major showstopper of this scheme is a strong transverse instability, which develops the surface ripples often attributed to the Rayleigh-Taylor-like (RT) mechanism triggered by the laser pressure. However, simulations indicate that the developing perturbations have a specific spectral structure, that cannot be consistently explained by the RT mechanism. Here we develop a three-dimensional (3D) theory of this instability, which shows that its linear stage is mainly driven by the strong electron-ion coupling, while the RT contribution is actually weak. The model provides instability spectral structure and growth rate, that agree well with large scale 3D particle-in-cell simulations. Numerical modelling shows, that the target is destroyed during the nonlinear instability phase by the induced plasma heating, which also triggers the merging of small filaments. Possible paths to instability mitigation are discussed.
|Working group||Theory and computation|