Electron-impact single ionisation of W$^{q+}$ ions: Experiment and theory for $\mathbf{11\leq q \leq 18}$

TL;DR

This study measures and calculates electron-impact single ionisation cross sections for tungsten ions with charge states 11 to 18, revealing discrepancies with existing data and highlighting limitations of current theoretical models.

Contribution

It provides new experimental data and extended theoretical calculations for W$^{q+}$ ions, improving understanding of ionisation processes in plasmas.

Findings

Experimental cross sections measured for 11 ≤ q ≤ 18

Theoretical calculations extended up to 150 keV

Discrepancies found with existing ADAS data at plasma temperatures

Abstract

Absolute cross sections for electron-impact single ionisation (EISI) of multiply charged tungsten ions (W$^{q+}$) with charge states in the range $ 11 \leq q \leq 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.