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 C^q+ (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.