Numerical simulations of scrape-off layer plasma turbulence: Role of parallel currents and sheath dissipation

The impact of sheath dissipation on scrape-off layer (SOL) turbulence and transport in magnetically confined plasmas is investigated using numerical simulations of a reduced two-field fluid model. By varying the sheath dissipation parameter over nearly two orders of magnitude while keeping the parallel particle loss rate fixed, the effects of sheath currents on blob dynamics, radial transport, and plasma profiles are isolated. Linear stability analysis shows that increasing sheath dissipation reduces the growth rate of interchange modes and shifts fluctuations to smaller spatial scales. Across the parameter scan, the simulations exhibit comparatively robust relative fluctuation levels of density across the SOL in the turbulence simulations. The scaling of transport-weighted poloidal blob size and radial velocities with the sheath dissipation parameter is accurately described by a blob velocity scaling theory. The simulation results are analyzed using a stochastic model, which describes the SOL fluctuations as a superposition of uncorrelated radially propagating pulses. The model captures the statistical properties of the simulated fluctuations and predicts an exponential mean-density profile with scale length Ln=V/σn, determined by the blob velocity V and parallel particle loss rate σn. The radial particle density profile steepens with increasing sheath dissipation, consistent with the change in blob propagation. Within the present reduced two-field model, these results demonstrate that effective sheath dissipation strongly influences filament scales, radial propagation, and the resulting SOL density profile. They provide a controlled reference for interpreting how changes in current closure may affect intermittent SOL transport, while motivating future three-dimensional studies with self-consistent parallel dynamics.