Effects of plasma resistivity in three-dimensional full-F gyro-fluid turbulence simulations

TL;DR

This study uses advanced gyro-fluid simulations to explore how plasma resistivity affects turbulence and confinement in tokamaks, revealing two distinct transport regimes and the impact of resistivity on plasma behavior.

Contribution

It introduces a comprehensive resistivity parameter scan in full-F gyro-fluid turbulence simulations with a GPU-accelerated code, highlighting new transport regimes and numerical conservation analysis.

Findings

High resistivity reduces confinement efficiency.

Parallel acceleration direction reverses at high resistivity.

Fluctuation amplitudes increase towards the edge.

Abstract

A full-F, isothermal, electromagnetic, gyro-fluid model is used to simulate plasma turbulence in a COMPASS-sized, diverted tokamak. A parameter scan covering three orders of magnitude of plasma resistivity and two values for the ion to electron temperature ratio with otherwise fixed parameters is setup and analysed. Simulations are performed with a new version of the FELTOR code, which is fully parallelized on GPUs. Each simulation covers a couple of milliseconds. Two transport regimes for high and low plasma resistivities are revealed. Beyond a critical resistivity the mass and energy confinement reduces with increasing resistivity. Further, for high plasma resistivity the direction of parallel acceleration is swapped compared to low resistivity. The integration of exact conservation laws over the closed field line region allows for an identification of numerical errors within the simulations. The electron force balance and energy conservation show relative errors on the order of $10^{-3}$ while the particle conservation and ion momentum balance show errors on the order of $10^{-2}$. Relative fluctuations amplitudes increase from below $1\%$ in the core to $15\%$ in the edge and up to $40\%$ in the scrape-off layer. Finally, three-dimensional visualisations using ray tracing techniques are displayed and discussed. The field-alignment of turbulent fluctuations in density and parallel current becomes evident.