Jacob Emil Mencke | Searcharxiv

arXiv2026

Derivation and application of sheath boundary conditions for drift-kinetic simulations in a linear plasma device based on a gyromoment approach

Boundary conditions for a drift-kinetic model at the collisional presheath entrance with perpendicular incidence of the magnetic field to the wall are derived and numerically implemented. The drift-kinetic model for the plasma is based on the expansion of the ion distribution function on a Hermite-Laguerre basis, and the evolution of the resulting gyromoments. A linear-plasma-device geometry is considered. Comparison with simpler simulations with previously used ad hoc boundary conditions is presented. For the new set of boundary conditions, a significant increase of the plasma outflow to the wall is observed, leading to a significantly smaller plasma density in the whole volume of the device.

physics.plasm-ph↗

arXiv2026

Comprehensive full-f drift-kinetic and delta-f gyrokinetic simulations of a linear plasma device based on the gyro-moment approach

First of a kind comprehensive full-f drift-kinetic (DK) and $\delta$-f gyrokinetic (GK) turbulent simulations are carried out in a linear plasma device. We self-consistently derive an electrostatic model including large-scale slowly-varying DK-ordered fields coupled to small-scale rapidly-fluctuating GK-ordered fields. By relying on the critical balance ordering, we show that the electrons are described by a drift-reduced Braginskii model while we rely on a Hermite-Laguerre spectral expansion for describing both the DK and GK parts of the ion distribution function. Global simulations are carried out using the parameters of the linear device LAPD, showing that the DK part of the ion distribution function is approximately a bi-Maxwellian. Fast spectral convergence both for the DK and GK Hermite-Laguerre expansion coefficients is observed, and that the GK fields do not affect the DK fields at the physical LAPD collisionality. Only when the collisionality is reduced and the source term is amplified for the GK fluctuations, an amplification of small-scale turbulent structures is observed. The findings are supported by linear results that show that the simulations are dominated by turbulent fluctuations that are Kelvin-Helmholz driven. Additionally, a GK Kelvin-Helmholz-like mode is observed in the low-GK-collisionality regime which can non-linearly drive small-scale structures.

physics.plasm-ph↗