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

The cross section for the ionisation process e+Fe+ to 2e+Fe2+ has been measured from below threshold up to an electron energy of 750 eV and at energies greater than 25 eV the overall accuracy is estimated to be +or-4.3%. The crossed electron-ion beams technique was used and there is evidence that the target ion beam contained a substantial component of metastable 4D and other long-lived excited Fe+ ions in addition to the ground-state 6D ions, but the ionisation data are likely to be directly relevant to Fe+ ion impurities sputtered from the walls of fusion devices. However, it is probable that the measured cross section is insensitive to the presence of these excited ions, at least at electron energies above about 30 eV. Comparison with theoretically predicted cross sections shows that the McGuire approach (1977) is in fair agreement with the experiment but that the parameters proposed by Lotz (1969) for his formulation do not yield a satisfactory fit to the measured data.