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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).