Multiple Ionization of Argon Induced by Carbon Ions at 20–500 keV/u Energies

We measure the multiple ionization cross-section ratios Rk1 of Ar impacted by Cq+ (q = 1−3) ions in the energy range of 20–500 keV/u. The measured ratios Rk1 increase with the projectile energy at lower energies, and reach the maximum at energies of 50–150 keV/u, then decrease for higher energies. We also use the classical over barrier ionization model to calculate the ratios Rk1, and the calculation results are in good agreement with the data, which suggest that the multiple ionization process is described by the sequential over-barrier ionization process.