Turbulence statistical analysis of the L-H transition and RMPs in KSTAR

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Abstract
We investigate the turbulence statistics associated with low-to-high confinement (L-H) transitions and externally applied resonant magnetic perturbations (RMPs) in KSTAR. Time-series fluctuations of electron density ne (BES), electron temperature Te (ECEI), and the time derivative of the poloidal magnetic field dBθ/dt (Mirnov coils) are analysed using information-geometric measures (information rate Γ and information length L = R Γdt), together with kurtosis κ and variance σ2. In low-density upper single-null plasmas (ne ∼ 1.2 × 1019 m−3), a ∼ 80 kHz magnetic mode coupling ne, Te, and dBθ/dt emerges prior to the L-H transition and persists into the ELMy H-mode. Edge-localised RMPs (ERMPs) suppress this coherent mode but enhance intermittency, producing frequent bursts that abruptly reshape the time- dependent Probability Density Functions (PDFs) and generate large spikes in Γ (with smaller changes in κ), signalling ERMP-driven departures from quasi-stationarity. The impact of ERMPs on background fluctuation levels depends on density, radial location, and the fluctuating variable itself (n ̃, T ̃, B ̇θ), whereas L provides a robust, regime- agnostic measure of cumulative statistical reorganisation and spatial decorrelation. In particular, at low density we observe weaker coupling between n ̃ and T ̃, along with a tendency toward decreased radial correlation—most clearly for T ̃—under ERMPs. Overall, information geometry cleanly captures intermittent events, quantifies non- equilibrium PDF evolution, and offers a compact, cross-diagnostic metric for assessing RMP effects on edge transport and correlation across densities, radial locations, and confinement states.
Funding Information
  • National Research Foundation of Korea (RS- 2023-00284119)

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