A simple method to evaluate double ionization of He by swift highly charged ions

Double ionization of He by impact of multiply charged ions is studied. Perturbative and non-perturbative regimes are analysed discriminating the influence of post-collisional effects. A simple exponential approximation, based on known theoretical or experimental single ionization cross sections and Bohr and Linhard predictions of the electron release distance, is shown to give an adequate description of existing experimental data. Saturation effects are shown to play an important role in the total cross section ratios of double and single ionization for non-perturbative collisions.