Improved atomic calculations of Si⁺ and W²⁺ for erosion experiments in DIII-D

A new calculation of electron-impact data for Si⁺ using the R-matrix with pseudo-states (RMPS) method has yielded ionization and excitation cross sections for both ground and excited states. The ground state ionization cross section is compared to experimental measurements and is in good agreement; thus, we also expect the calculated excited state cross sections (for which no experimental measurements exist) to have high accuracy. The new calculation uses a basis set that is three times the size of previous R-matrix calculations, allowing cross sections to be extended to higher energies, and provides the first excited state ionization cross sections for Si⁺. The atomic data is used to generate S/XB coefficients, which can be combined with spectroscopic measurements to infer time-resolved erosion and re-deposition rates. A new ionization calculation for W²⁺, needed to determine W re-deposition rates, is currently underway using the RMPS method. The new Si⁺ and W ionization calculations will be benchmarked over a range of plasma conditions during upcoming experiments in DIII-D using the DiMES probe and new UV spectroscopy capabilities.