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Collisional-radiative data for tokamak disruption mitigation modeling

Prashant Sharma, Christopher J. Fontes, Dmitry V. Fursa, Igor Bray, Mark Zammit, James Colgan, Hyun-Kyung Chung, Nathan Garland, Xian-Zhu Tang

Abstract

Effective tokamak disruption mitigation is crucial for ensuring the safety and integrity of fusion power reactors. Accurate collisional-radiative (CR) modeling of a radiative plasma is a critical component in predictive disruption mitigation design. In this paper, we focus on quasi-steady-state CR modeling applicable to the current quench phase of a tokamak disruption. We employ the ATOMIC collisional-radiative code from the Los Alamos suite and the newly developed Fusion Collisional-Radiative (FCR) code to model the atomic processes, providing high-fidelity data for radiative power loss, as well as average and effective charge states for hydrogen, helium, neon, and argon plasma species over a wide range of tokamak-relevant electron temperatures and electron densities. Fine-structure-resolved CR models are used for hydrogen and helium plasma species, while configuration-average CR models are implemented for neon and argon plasma species. The calculated values are compared with the superconfiguration CR model (FLYCHK) and the commonly used coronal equilibrium approximation to demonstrate the advantages and limitations of each model. To facilitate coupling of high-fidelity CR data to plasma simulation models, we represent the ATOMIC/FCR results over the relevant plasma parameter range using a smooth tensor product B-spline surface in electron temperature and electron density. This approach yields compact coefficient tables that can be evaluated efficiently while preserving spline smoothness across the domain. These data were previously used to examine ways to minimize runaway electrons in a tokamak current quench, and they are now made available in easy-to-use forms for community use and benchmarking.

Collisional-radiative data for tokamak disruption mitigation modeling

Abstract

Effective tokamak disruption mitigation is crucial for ensuring the safety and integrity of fusion power reactors. Accurate collisional-radiative (CR) modeling of a radiative plasma is a critical component in predictive disruption mitigation design. In this paper, we focus on quasi-steady-state CR modeling applicable to the current quench phase of a tokamak disruption. We employ the ATOMIC collisional-radiative code from the Los Alamos suite and the newly developed Fusion Collisional-Radiative (FCR) code to model the atomic processes, providing high-fidelity data for radiative power loss, as well as average and effective charge states for hydrogen, helium, neon, and argon plasma species over a wide range of tokamak-relevant electron temperatures and electron densities. Fine-structure-resolved CR models are used for hydrogen and helium plasma species, while configuration-average CR models are implemented for neon and argon plasma species. The calculated values are compared with the superconfiguration CR model (FLYCHK) and the commonly used coronal equilibrium approximation to demonstrate the advantages and limitations of each model. To facilitate coupling of high-fidelity CR data to plasma simulation models, we represent the ATOMIC/FCR results over the relevant plasma parameter range using a smooth tensor product B-spline surface in electron temperature and electron density. This approach yields compact coefficient tables that can be evaluated efficiently while preserving spline smoothness across the domain. These data were previously used to examine ways to minimize runaway electrons in a tokamak current quench, and they are now made available in easy-to-use forms for community use and benchmarking.
Paper Structure (14 sections, 25 equations, 7 figures, 1 table)

This paper contains 14 sections, 25 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Collisional-Radiative Modeling Approach
  3. Coupling the CR data to plasma modeling
  4. ATOMIC data: Hydrogen, Helium, Neon, and Argon
  5. Radiative power loss
  6. Average charge state
  7. Effective charge state
  8. Comparisons with superconfiguration CE model and CR model
  9. Model reduction with coronal equilibrium approximations
  10. CR model reduction with superconfiguration averaging
  11. Tensor-Product B-spline Surface Fitting
  12. Conclusion
  13. Acknowledgement
  14. Data Availability

Figures (7)

  • Figure 1: Variation of radiative power loss rate with respect to the electron temperature for (a) hydrogen, (b) helium, (c) neon, and (d) argon. The hydrogen results are calculated using the FCR code sharma2026hybrid, while the helium, neon, and argon results are calculated using the ATOMIC code Fontes2015. The radiative power loss rates are expressed in W-cm$^3$, where 1 W = 10$^7$ erg-s$^{-1}$.
  • Figure 2: Radiative power loss calculated for neon as a function of electron temperature for the electron density of $n_e$ = 10$^{14}$ cm$^{-3}$: (a) Contribution of bound-bound, free-bound, and free-free transitions in the total radiative power loss. (b) Contribution of different charge states in the total radiative power loss. All results shown are calculated using the ATOMIC code Fontes2015. The radiative power loss rates are expressed in W-cm$^3$, where 1 W = 10$^7$ erg-s$^{-1}$.
  • Figure 3: Variation of average charge state with respect to the electron temperature for (a) hydrogen, (b) helium, (c) neon, and (d) argon. The hydrogen results are calculated using the FCR code sharma2026hybrid, while the helium, neon, and argon results are calculated using the ATOMIC code Fontes2015.
  • Figure 4: Variation of effective charge state with respect to the electron temperature for (a) helium, (b) neon, and (c) argon. All results shown are calculated using the ATOMIC code Fontes2015.
  • Figure 5: Variation of the radiative power loss rate as a function of electron temperature for (a) hydrogen, (b) helium, (c) neon, and (d) argon. All results are calculated within the FCR framework using a superconfiguration-based atomic-state representation. The figure compares three models: a full coronal model, a basic coronal model, and a full collisional-radiative model incorporating all relevant atomic processes and their inverse reactions. The definitions of the coronal limits are described in the text. The radiative power loss rates are expressed in W-cm$^3$, where 1 W = $10^{7}$ erg s$^{-1}$.
  • ...and 2 more figures