Description
Intermittent, large-amplitude fluctuations dominate cross-field transport of particles and heat in the scrape-off layer (SOL) of magnetically confined plasmas. These fluctuations are investigated using numerical turbulence simulations of both a two-dimensional (2D) reduced fluid model [1] and a three-dimensional (3D) full-torus gyrofluid model (FELTOR) [2]. The 2D model describes drift–interchange dynamics with sheath dissipation in the SOL, while the 3D simulations resolve the full toroidal geometry with electromagnetic effects. In both cases, the SOL is characterized by radial motion of blob-like filament structures that give rise to strong intermittency and broad time-averaged particle density profiles.
The fluctuations are analyzed within a statistical framework describing the fluctuations as a superposition of uncorrelated pulses [3]. A novel deconvolution algorithm is for the first time applied to numerical simulation data [4], revealing blob amplitudes and arrival times from synthetic probes in turbulence simulations. Using these pulse parameters, the time-averaged particle density profile is reconstructed from the statistical properties of the fluctuations alone. The reconstructed profiles are in close agreement with those obtained directly from the simulations, demonstrating that the SOL particle density profile can be understood as a superposition of filamentary events. These results suggest the absence of a distinct background plasma component in the SOL, with the profile arising entirely from filament structures.
The deconvolution procedure further enables sampling of other plasma quantities at blob arrival times. With simulation data the available plasma quantities are numerous as well as directly available. This allows investigation of correlations between blob amplitude, radial velocity, particle flux, and other quantities, providing new insight into filament dynamics and cross-field transport mechanisms. Combined, these results provides strong evidence in support of stochastic modelling, describing all the SOL plasma and its fluctuations as due to uncorrelated blob-like filaments, and provides a robust framework for analyzing multi-field correlations.
References
$[1]$ S. Brynjulfsen and O. E. Garcia, "Numerical simulations of scrape-off layer plasma
turbulence: Role of parallel transport and particle losses" Phys. Plasmas 33, 022301 (2026)
$[2]$ S. Brynjulfsen et al., "Fluctuation-driven cross-field plasma transport in FELTOR turbulence simulations of the TCV-X23 scenario" submitted to Plasma Phys. Control. Fusion (2026)
$[3]$ O. E. Garcia et al., "Stochastic modelling of intermittent fluctuations in the scrape-off layer:
Correlations, distributions, level crossings, and moment estimation" Phys. Plasmas 23, 052308 (2016)
$[4]$ S. Ahmed et al., "Reconstruction of intermittent time series as a superposition of pulses" Phys. Rev. E 107, 054222 (2023)