Atomic collisional data for neutral beam modeling in fusion plasmas

Hill, C. and Dipti and Heinola, K. and Dubois, A. and Sisourat, N. and Taoutioui, A. and Agueny, H. and Tőkési, K. and Ziaeian, I. and Illescas, C. and Jorge, A. and Méndez, L. and Kadyrov, A.S. and Antonio, N.W. and Kotian, A.M. and Kirchner, T. and Leung, A.C.K. and Ko, J. and Lee, J.K. and Marchuk, O. and O’Mullane, M.G. and Litherland-Smith, E. and Pokol, G.I. and Asztalos, O. and Balazs, P. and Wu, Y. and Jia, C.C. and Liu, L. and Wang, J.G. (2023) Atomic collisional data for neutral beam modeling in fusion plasmas. Nuclear Fusion, 63 (12). 125001. ISSN 0029-5515 (https://doi.org/10.1088/1741-4326/acf5da)

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Abstract

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) and from plasma impurities with which they interact (e.g. charge exchange recombination spectroscopy). This paper reviews and compares 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 that previously accepted at fusion-relevant energies. Coefficients for an empirical fit function to this cross section and to that of the first excited states of H 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 modeling 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 to 2022; this project brought together ten 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.

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