Description
Owing to the possibility of highly localised power deposition, electron cyclotron-range microwaves are an almost ubiquitous tool in tokamak experiments, used for heating (ECRH) and current drive (ECCD). They are foreseen as the main heating source for the ITER project [1] and are additionally envisioned to provide instability mitigation and tailored control of current and pressure profiles. However, previous work [2,3] has shown that quasilinear simulations neglecting turbulence effects tend to significantly overestimate the efficacy of ECRH/ECCD performance, with experimental observations indicating that the presence of turbulence jeopardises the localisation especially. The discrepancy with experimental observations is generally attributed to two mechanisms: microwave beam broadening caused by turbulent plasma density fluctuations, and wave-enhanced turbulent transport of suprathermal electrons.
A turbulence-inclusive, multidiagnostic Fokker-Planck framework was previously introduced [4], allowing for the strongly constrained optimisation of unknown plasma parameters. The ad-hoc radial transport of suprathermal electrons in particular, can be prescribed to match a set of complementary fast-electron diagnostic measurements on the TCV tokamak. The current contribution describes two recent extensions to the framework: the coupling to the RAPTOR observer [5] that assimilates available internal profile measurements into a transport simulation, and the introduction of more adequate momentum-space basis functions for suprathermal electron transport, based on gyrokinetic simulations performed with GENE [6] and theoretical considerations. The resulting self-consistent framework, armed with a small set of appropriate transport basis functions, allows for the automatic optimisation of hyperparameters to match experimental data. Results from a dedicated experimental campaign on the TCV tokamak will be presented as proof of principle, aiming at the characterisation of fast-electron transport in ECCD scenarios across a broad range of operational parameters, with particular focus on the implications for current drive and the resulting safety factor profile.
[1] I.T.E.R. Organisation, ITER research plan within the staged approach, ITR-18-003 (2018)
[2] S. Coda et al, Nuclear Fusion, 43(11), (2003) 1361
[3] J.A. Cazabonne Investigation of the interplay between Electron-Cyclotron waves, suprathermal electrons and turbulence in tokamak plasmas, EPFL, (2023) No. 10171
[4] E. Devlaminck et al, Proceedings of the 51st EPS Conference on Controlled Fusion and Plasma Physics, (2025) P4.163
[5] S. Van Mulders et al, Nuclear Fusion, 66(2), (2026) 026026
[6] F. Jenko et al, Physics of Plasmas, 7(5), (2000) 1904