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Absolute cross sections for electron-impact single ionisation (EISI) of multiply charged tungsten ions (W q+ ) with charge states in the range 11 ≤ q ≤ 18 in the electron-ion collision energy ranges from below the respective ionisation thresholds up to 1000 eV were measured employing the electron-ion crossed-beams method. In order to extend the results to higher energies, cross section calculations were performed using the subconfiguration-averaged distorted-wave (SCADW) method for electron-ion collision energies up to 150 keV. From the combined experimental and scaled theoretical cross sections rate coefficients were derived which are compared with the ones contained in the ADAS database and which are based on the configuration-averaged distorted wave (CADW) calculations of Loch et al. [Phys. Rev. A 72, 052716 (2005)]. Significant discrepancies were found at the temperatures where the ions investigated here are expected to form in collisionally ionised plasmas. These discrepancies are attributed to the limitations of the CADW approach and also the more detailed SCADW treatment which do not allow for a sufficiently accurate description of the EISI cross sections particularly at the ionisation thresholds.

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The cross section for electron-impact single ionisation of ions has been calculated by using two different approaches, i.e. the subconfiguration averaged distorted-wave (SCADW) method and the more involved level-to-level distorted-wave (LLDW) method. Both methods are found to yield very similar results except for the excitation-autoionisation (EA) channels that straddles the ionisation threshold. Accordingly, a hybrid theoretical cross section where the EA SCADW cross section is replaced by its LLDW counterpart is in good agreement with the experimental result from an electron-ion crossed-beams experiment. This is in contrast to pure SCADW calculations for and neighbouring charge states which exhibit significant deviations from the experimental near-threshold cross sections of Schury et al (2020 J. Phys. B: At. Mol. Opt. Phys. 53 015201).

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Recently, we have demonstrated (Jin et al 2020 J. Phys. B: At. Mol. Opt. Phys. 53 075201) that a hybrid subconfiguration-average and level-to-level distorted wave treatment of electron-impact single ionisation (EISI) of W14+ ions represents an accurate and manageable approach for the calculation of EISI cross sections of a complex ion. Here we demonstrate the more general validity of this approach by comparing hybrid cross sections for EISI of W15+ and W16+ with the recent experimental results of Schury et al (2020 J. Phys. B: At. Mol. Opt. Phys. 53 015201). Our calculations also account for the resonant-excitation double autoionisation (REDA) process which is important in the electron energy range 370–600 eV and for the possible presence of initially metastable ions in the experiment.

Synopsis During recent years we have developed a new high-current electron gun for the Giessen electron-ion crossed-beams experiment aiming at an extension of the previously available collision-energy range of 1–1000 eV to 3500 eV. Here, we report on the first measurements of absolute cross sections for electron-impact ionisation of multiply charged xenon ions employing the new electron gun. Comparisons with available experimental and theoretical data from the literature provide convincing evidence that the new electron gun can be operated reliably over the entire design energy-range.

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