Enhanced Final State Resolution for Atomic Data from R-matrix with Pseudostates Calculations and Collisional Radiative Modeling for He, Si+, and W2+ with Applications to Plasma Diagnostics

Abstract

Fusion reactors based on magnetic confinement are a promising potential source of clean energy. The understanding of these plasma environments is greatly assisted by the use of accurate atomic data in plasma modeling and spectroscopic diagnostics. The present work seeks to improve the atomic data available for tungsten and silicon for wall erosion diagnosis, and neutral helium for plasma edge diagnostics.

Several new electron-impact calculations have been performed, all requiring large-scale computation on local and remote supercomputers with a common theme on the importance of excited state ionization. An existing set of neutral He ionization cross sections was extended to high temperatures using Bethe high energy limit points and Younger functions; this data was used in collisional radiative modeling to produce generalized rate coefficients for use in plasma diagnostics.

A new set W$^{2+}$ electron-impact ionization cross sections, including excited states, was calculated using the $R$-matrix with pseudostates method. This is the first time non-perturbative ionization cross sections have been generated for this ion. The calculation was extended to the high temperatures experienced by sputtered tungsten ions. A new capability for LS-resolved $R$-matrix calculations was developed: the identification of the parents of pseudostates allowed for the ionized final state to be identified, producing LSJ-resolution via Sampson branching ratios. This calculation was combined with an earlier excitation calculation and S/XB coefficients were generated using collisional-radiative modeling. These coefficients will allow for the distinction between gross and net erosion of eroded tungsten.

New Si$^+$ electron-impact excitation and ionization cross sections were calculated using the $R$-matrix with pseudostates method. The ionization calculation was performed in the same way as W$^{2+}$, while the excitation calculation used a semi-relativistic Breit-Pauli Hamiltonian. This is the first non-perturbative ionization data for Si$^+$ and is the first Si$^+$ calculation to use pseudostates for excitation data. The ionization data was resolved for both the initial and final states. Collisional-radiative modeling was used to produce S/XB coefficients for erosion diagnostics for silicon carbide plasma facing components.

This work is in support of ongoing work using high-resolution ultraviolet spectroscopy at the DIII-D tokamak and the Auburn University Compact Toroidal Hybrid experiment.