Double Ionization of Helium by Partially Stripped Oxygen Ions

New measurement of the ratio of the double ionization cross section to that of the single ionization of helium induced by 2.0-7.5 MeV partially stripped O^q+ ion (q = 1,2,3,4) is presented. Combining the measured data with the Olson-Schlachter scaling, the double ionization cross section of helium by partially stripped oxygen ion is obtained. It is found that the v/q_eff dependence of the obtained double ionization cross section agrees well with the (v/q_eff)^-4 law.