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

We measure the multiple ionization cross-section ratios R-k1 of Ar impacted by Cq+ (q = 1-3) ions in the energy range of 20-500 keV/u. The measured ratios R-k1 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 R-k1, 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.