Particle scattering in magnetised plasmas: a theoretical and numerical approach

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School of Science | Doctoral thesis (article-based) | Defence date: 2024-01-26
Degree programme
72 + app. 56
Aalto University publication series DOCTORAL THESES, 17/2024
The intricate dynamics of charged particles within plasmas are mainly shaped by their collisional interactions. As a result, it is crucial to address these phenomena through both theoretical and numerical approaches. In pursuit of this objective, this work embarks on reviewing the formal derivation of the Vlasov equation, followed by an extensive exploration of Coulomb scattering, elucidating the Landau collision integral and its underlying characteristics. Furthermore, we delve into the nonconventional neoclassical theory for toroidal systems, providing the theoretical framework for the subsequent numerical findings. Utilizing the ELMFIRE code, gyrokinetic simulations employ a discrete Landau collision integral, ensuring the conservation of energy and momentum. Tailored to conservation laws, a specific binary collision model provides valuable insights into variations in impurity density arising from steep gradients in density and temperature profiles. The analysis compares Landreman-Fülöp- Guszejnov model's theory with neoclassical predictions and ELMFIRE data. Remarkably, within the analytical theory's validity, numerical agreement is 5-10%, especially for δ<0.4 with low charge numbers. Yet, within the pedestal region, the Landreman-Fülöp-Guszejnov framework may not be directly applicable due to pronounced gradients. Furthermore, a novel analysis explores the correlation between turbulent transport and the radial electric field. Using Lower Hybrid (LH) heating operator in an FT-2 tokamak at off-axis and onaxis reveals heightened turbulence at r/a=0.55 during a 70μs simulation. Turbulence induces noticeable fluctuations in the radial electric field profile, with strong high-shearing flow in the former and neoclassical dominance in the latter. These findings align with prior research, suggesting a robust shearing phenomenon, reinstating transport equilibrium. In conclusion, to enhance the central theme of this dissertation, we investigate the formal derivation of a collisional bracket from the Landau collision integral using the metriplectic bracket formulation for dissipative systems. This theoretical framework is then applied to the guiding center Vlasov-Maxwell-Landau model, resulting in a specific collisional bracket that ensures energy and momentum conservation. The implications of this finding are explored within broader frameworks, including the electromagnetic gyrokinetic case, offering a theoretical culmination to this dissertation.
Supervising professor
Groth, Mathias, Prof., Aalto University, Department of Applied Physics, Finland
Thesis advisor
Hirvijoki, Eero, Dr., Aalto University, Department of Mechanical Engineering, Finland
Kiviniemi, Timo, Dr., Aalto University, Department of Applied Physics, Finland
plasma dynamics, fusion plasma
Other note
  • [Publication 1]: F. Zonta, R. N. Iorio, J.W. Burby, C. Liu and E. Hirvijoki. Dispersion relation for gauge-free electromagnetic drift kinetics. Physics of Plasmas, Volume 28, Issue 9, 092504, August 2021.
    DOI: 10.1063/5.0058118 View at publisher
  • [Publication 2]: R. N. Iorio and E. Hirvijoki. An energy and momentum conserving collisional bracket for the guiding-centre Vlasov-Maxwell-Landau model. Journal of Plasma Physics, Volume 87, Issue 4, 835870401, July 2021.
    DOI: 10.1017/S0022377821000696 View at publisher
  • [Publication 3]: R. N. Iorio, L. Chone, E. Gusakov, T. P. Kiviniemi, S.Lashkul and S.Leerink. Revisiting the improved core confinement simulations for FT-2 tokamak. Contribution to Plasma Physics, Volume 62, Issue 5-6, e202100187, March 2022.
    DOI: 10.1002/ctpp.202100187 View at publisher
  • [Publication 4]: R. N. Iorio, T. P. Kiviniemi, E. Hirvijoki, L. Chone, F. Albert and S. Leerink. Numerical study of limits of neoclassical theory in the plateau regime in the presence of impurities. Contribution to Plasma Physics, November 2023.
    DOI: 10.1002/ctpp.202300066 View at publisher