Numerical simulations of scrape-off layer plasma turbulence: Role of parallel transport and particle losses

This study investigates cross-field particle transport and intermittent fluctuations in the boundary region of magnetically confined plasmas using numerical turbulence simulations based on a reduced two-field fluid model. The model captures turbulent dynamics and blob-like structures in the drift plane perpendicular to the magnetic field, while parametrizing parallel losses in the scrape-off layer through sheath interactions at material surfaces. A systematic analysis of fluctuation statistics is performed by varying the parallel loss rate parameter. Results show that increasing parallel losses steepens the radial particle density profile, enhances the linear growth rate, reduces the dominant fluctuation length scale, increases the relative fluctuation level, and amplifies the intermittency of fluctuations. Despite these changes, the statistical properties of the fluctuations remain consistent across all parallel loss rates. Large-amplitude bursts are well described by a two-sided exponential pulse function, with peak amplitudes and waiting times following exponential distributions, fluctuations obeying Gamma distributions, and frequency spectra exhibiting a Lorentzian shape. These features are accurately captured by a stochastic model based on the superposition of uncorrelated pulses. The methodology presented here offers a robust framework for verifying fluctuation statistics in more advanced boundary turbulence simulation codes.