Multi-electron Process Of Helium In The Strong Purtubative Energy Range

Single and double ionization of Helium induced by C^q+,O^q+(q=1-3) ions were studied both in experiment and in theory. The double-to single-ionization ratios R were measured by coincidence between time of flight (TOF) and position information. The energy of these ions ranges from 0.2MeV to 5.8MeV. This work was performed on the 2×1.7MV tandem accelerator in Lanzhou University.The experimental results indicated that when the collision energy is about 200 or 300keV/amu, the value of R reaches the maximum, not only in the direct ionization process, but also in the charge exchange process. Meanwhile, a new theory model, based on the classical over-the-barrier model is performed, which aims to include the ionization process.The comparison between the different experimental values and the theoretical calculation shows a qualitative agreement, in particular showing a maximum occurring at about 250 keV/amu.