The injection of energetic neutral particles into the plasma of magnetic confinement fusion reactors is a widely-accepted method for heating such plasmas; various types of neutral beam are also used for diagnostic purposes. Accurate atomic data are required to properly model beam penetration into the plasma and to interpret photoemission spectra from both the beam particles themselves (e.g. Beam Emission Spectroscopy, BES) and from plasma impurities with which they interact (e.g. Charge Exchange Recombination Spectroscopy, CXRS).
This paper compares and reviews theoretical methods for calculating ionization, excitation and charge exchange cross sections applied to several important processes relevant to neutral hydrogen beams, including H + Be4+ and H + H+. In particular, a new cross section for the proton-impact ionization of H (1s) is recommended which is significantly larger than the previously accepted cross section at fusion-relevant energies. Coefficients for an empirical fit function to this cross section are provided and uncertainties estimated. The propagation of uncertainties in this cross section in modeling codes under JET-like conditions has been studied and the newly-recommended values determined to have a significant effect on the predicted beam attenuation.
In addition to accurate calculations of collisional atomic data, the use of these data in codes modeling beam penetration and photoemission for fusion-relevant plasma density and temperature profiles is discussed. In particular, the discrepancies in the modelling of impurities are reported.
The present paper originates from a Coordinated Research Project (CRP) on the topic of fundamental atomic data for neutral beam modeling that the International Atomic Energy Agency (IAEA) ran from 2017-2022; this project brought together 10 research groups in the fields of fusion plasma modeling and collisional cross section calculations. Data calculated during the CRP is summarized in an Appendix and is available online in the IAEA?s atomic database, CollisionDB.