Electron-impact excitation of Fe 21+ , including n =4 levels

We have carried out a 204-level close-coupling (CC) calculation for B-like Fe using the R-matrix method in conjunction with the intermediate-coupling frame transformation method as part of the RmaX Network programme of work to provide atomic data for x-ray processes. We have also carried out two 125-level CC calculations to enable us to illustrate the effect of n = 4 levels on collision data involving n = 2 and 3 levels and to provide a quantitative guide to the uncertainty resulting from the partial resolution of resonances. From our 204-level CC calculation, we have generated effective collision strengths over T = 10 5 –10 8 K for all 20 706 inelastic transitions, which is an order of magnitude larger than has been generated hitherto. We provide illustrative comparisons with the results of previous workers, where possible, and find a broad accord. The consistent and comprehensive set of data that we have generated (energy levels, radiative rates and effective collision strengths, including Born limits) is of great relevance to studies utilizing spectral observations from the new high-resolution x-ray satellites Chandra and XMM–Newton, as well as being necessary for the collisional– radiative modelling of metallic impurities that will arise in the next generation of magnetic fusion reactors.