Plasma flows and turbulence in gyrokinetic simulations

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School of Science | Doctoral thesis (article-based) | Defence date: 2025-06-26
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Authors

Date

2025

Department

Teknillisen fysiikan laitos
Department of Applied Physics

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Mcode

Degree programme

Language

en

Pages

100 + app. 51

Series

Aalto University publication series Doctoral Theses, 126/2025

Abstract

One of the primary challenges in the nuclear fusion research is comprehending and controlling plasma turbulence in fusion reactors. With the advancement of computational power in recent years, gyrokinetic codes have emerged as pivotal tools in elucidating the mechanisms underlying plasma turbulence. This thesis presents the utilization of two gyrokinetic codes, ELMFIRE and Gyrokinetic Electromagnetic Numerical Experiment (GENE), to investigate plasma turbulence in the core and edge regions of the Fisichiskii Tokamak-2 (FT-2) tokamak. To more comprehensively predict the scrape-off layer physics in the FT-2 tokamak, several code changes are implemented in ELMFIRE to recycle the particles exiting the simulation domain in the toroidal direction closer to the poloidal limiters in FT-2. Using radial particles source profiles from ASTRA simulations along with recycling plasma ions and electrons closer to the limiters exhibited qualitative agreement of the electron density profiles within 30% of the profiles measured by Langmuir probes. However, the electron temperature profiles are predicted systematically higher by a factor of 1.5 to 2 with the respective Langmuir probe measurement, still within the uncertainties of measurements. Using the GENE code, the Geodesic acoustic mode (GAM) intermittency in the core of FT-2 is studied by performing a global non-linear simulation. The simulation results revealed intermittency in GAMs close to the loworder rational surface (q=3). This finding constitutes the first observation of GAM intermittency in a gyrokinetic simulation. The underlying cause of this GAM intermittency is attributed to the non-linear coupling between GAMs and turbulence at this radial location. Furthermore, the density fluctuations exhibited intermittency at the same radial location, confirming the non-linear coupling between GAMs and turbulence. The impact of the Krook-type source operators on the GAM dynamics in the GENE simulations is investigated. Global non-linear simulations showed that the GAM amplitude increases with increasing Krook-type source operator values, driven by an increased GAM drive. The zonal flows amplitude decreases with the increasing value of the Krook-type source operators in the center region. Notably, the GAM damping in the center region increases by 15 to 100% with increasing operator values. Despite the GAMs exhibiting intermittency, their quiescent and active periods differ with operator values.

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Supervising professor

Groth, Mathias, Prof., Aalto University, Department of Applied Physics, Finland

Thesis advisor

Kiviniemi, Timo, Dr., Aalto university, Department of Applied Physics, Finland
Chôné, Laurent, Dr., University of Helsinki, Finland

Keywords

plasma, turbulence, nuclear fusion, GAMs, simulations

Other note

Parts

  • [Publication 1]: F. Albert, L. Chôné, T. P. Kiviniemi, O. Kaledina, S. Shatalin, A. D. Gurchenko, A. Altukhov, E. Gusakov, M. Kantor, D. Kouprienko, S. Lashkul. Effect of toroidal particle sources on SOL physics in the FT-2 tokamak. Contributions to Plasma Physics, 2022, 62(5-6), e202100192, March 2022.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202208104755
    DOI: 10.1002/ctpp.202100192 View at publisher
  • [Publication 2]: F. Albert, T. P. Kiviniemi, L. Chôné, S. Janhunen, S. Leerink, E. Hirvi- joki, R. Iorio. GENE simulations of GAM-turbulence interactions in FT-2 tokamak. Plasma Physics and Controlled Fusion, 2025, February 2025.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202503192934
    DOI: 10.1088/1361-6587/adab1a View at publisher
  • [Publication 3]: F. Albert, L. Chôné, T. P. Kiviniemi. Impact of Krook-type source opera- tors on GAM dynamics in GENE simulations. Submitted to Contribution to Plasma Physics, March 2025

Citation

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https://urn.fi/URN:ISBN:978-952-64-2619-8

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[diss] Perustieteiden korkeakoulu / SCI