A measurement of the cross section for electron impact ionisation of Ni

The cross section for the ionisation process e+Ni+ to 2e+Ni2+ has been measured for electron energies from threshold up to 780 eV using the electron-ion beams technique. The total error at a 90% confidence level is estimated to be +or-5% for energies greater than 18 eV. There is evidence that the target ion beam contained a substantial fraction of 4F and 2F metastable ions as well as 2D ground-state ions. However, since the ions were produced in a sputter ion source, the measured cross section is directly relevant to ionisation of Ni+ ions sputtered from the walls of the fusion plasma device. The semi-empirical formula of Lotz (1969) grossly overestimates the cross section, whereas the scaled Born cross section of McGuire (1977) is reasonably accurate at energies above 60 eV.