Plasma-neutral collision operators for hydrogen isotopes: kinetic and gyrokinetic descriptions, comparison to fluid
Abstract
Plasma-neutral interactions critically affect the edge dynamics of magnetically confined fusion devices. Neutral atoms modify ion and electron velocity distributions, potentially affecting local instabilities Standard fluid models simplify these processes (namely charge exchange, ionization and recombination) using Maxwellian assumptions and linearized source terms. We revisit these assumptions for a hydrogen plasma interacting with hydrogen atoms. We derive plasma-neutral interaction terms in the kinetic and gyrokinetic frameworks. Accounting for velocity-dependent differential cross-sections, the model captures the kinetic impact of inelastic collisions on ions and electrons beyond energy and momentum exchange. We demonstrate that the fluid moments of the kinetic model reduce to standard fluid source terms under the appropriate assumptions of Maxwellianity and linearity. We compare the kinetic model with fluid models through their effects on distribution functions and fluid moments. Substantial discrepancies are observed, even for Maxwellian distributions. For charge exchange, the kinetic model yields momentum and energy exchange rates up to twice those predicted by fluid descriptions. We show that a fluid treatment of ionization greatly overestimates the mean kinetic energy of the produced electrons. These results highlight the limitations of fluid descriptions and the importance of kinetic effects in edge-plasma momentum and energy exchange.
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BibTeX
@misc{protais2026plasmaneutral,
title = {{Plasma-neutral collision operators for hydrogen isotopes: kinetic and gyrokinetic descriptions, comparison to fluid}},
author = {Matthieu Protais and Guilhem Dif-Pradalier and Yanick Sarazin and Virginie Grandgirard and Yannick Marandet and Srikanth Sureshkumar and Naren Varadarajan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.15090},
eprint = {2610.15090},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.15090},
note = {CC BY-NC-SA 4.0},
}
RIS
TY - UNPB
TI - Plasma-neutral collision operators for hydrogen isotopes: kinetic and gyrokinetic descriptions, comparison to fluid
AU - Matthieu Protais
AU - Guilhem Dif-Pradalier
AU - Yanick Sarazin
AU - Virginie Grandgirard
AU - Yannick Marandet
AU - Srikanth Sureshkumar
AU - Naren Varadarajan
PY - 2026
DA - 2026/10/10
PB - arXiv
DO - 10.48550/arxiv.2610.15090
UR - https://arxiv.org/abs/2610.15090
AB - Plasma-neutral interactions critically affect the edge dynamics of magnetically confined fusion devices. Neutral atoms modify ion and electron velocity distributions, potentially affecting local instabilities Standard fluid models simplify these processes (namely charge exchange, ionization and recombination) using Maxwellian assumptions and linearized source terms. We revisit these assumptions for a hydrogen plasma interacting with hydrogen atoms. We derive plasma-neutral interaction terms in the kinetic and gyrokinetic frameworks. Accounting for velocity-dependent differential cross-sections, the model captures the kinetic impact of inelastic collisions on ions and electrons beyond energy and momentum exchange. We demonstrate that the fluid moments of the kinetic model reduce to standard fluid source terms under the appropriate assumptions of Maxwellianity and linearity. We compare the kinetic model with fluid models through their effects on distribution functions and fluid moments. Substantial discrepancies are observed, even for Maxwellian distributions. For charge exchange, the kinetic model yields momentum and energy exchange rates up to twice those predicted by fluid descriptions. We show that a fluid treatment of ionization greatly overestimates the mean kinetic energy of the produced electrons. These results highlight the limitations of fluid descriptions and the importance of kinetic effects in edge-plasma momentum and energy exchange.
ER -