Investigation of the Effect of Resistivity on Scrape Off Layer Filaments using Three Dimensional Simulations

TL;DR

This study uses 3D simulations to explore how increased parallel resistivity influences filament dynamics in the tokamak SOL, revealing that higher resistivity can lead to faster filament velocities and broader plasma profiles.

Contribution

It provides new insights into the impact of parallel resistivity on filament transport, extending understanding of SOL profile shaping in tokamaks.

Findings

Higher resistivity increases filament velocities for larger filaments.

Resistivity reduces parallel currents and enhances polarization currents.

Broader SOL profiles may result from increased resistivity.

Abstract

The propagation of filaments in the Scrape Off Layer (SOL) of tokamaks largely determine the plasma profiles in the region. In a conduction limited SOL, parallel temperature gradients are expected, such that the resistance to parallel currents is greater at the target than further upstream. Since the perpendicular motion of an isolated filament is largely determined by balance of currents that flow through it, this may be expected to affect filament transport. 3D simulations have thus been used to study the influence of enhanced parallel resistivity on the dynamics of filaments. Filaments with the smallest perpendicular length scales, which were inertially limited at low resistivity (meaning that polarization rather than parallel currents determine their radial velocities), were unaffected by resistivity. For larger filaments, faster velocities were produced at higher resistivities, due to two mechanisms. Firstly parallel currents were reduced and polarization currents were enhanced, meaning that the inertial regime extended to larger filaments, and secondly a potential difference formed along the parallel direction so that higher potentials were produced in the region of the filament for the same amount of current to flow into the sheath. These results indicate that broader SOL profiles could be produced at higher resistivities.