L-mode filament characteristics on MAST as a function of plasma current measured using visible imaging

TL;DR

This study investigates how filament characteristics at the edge of MAST tokamak plasmas vary with plasma current, revealing that increased current reduces filament velocity and size, impacting particle transport to the divertor.

Contribution

It provides new insights into the dependence of filament dynamics on plasma current in L-mode plasmas using visible imaging on MAST.

Findings

Filament radial velocity decreases with higher plasma current.

Filament size reduces as plasma current increases.

Filament behavior influences particle profiles at the divertor.

Abstract

Clear filamentary structures are observed at the edge of tokamak plasmas. These filaments are ejected out radially and carry plasma in the far Scrape Off Layer (SOL) region, where they are responsible for producing most of the transport. A study has been performed of the characteristics of the filaments observed in L-mode plasma on MAST, using visible imaging. A comparison has then been made with the observed particle and power profiles obtained at the divertor as a function of the plasma current. The radial velocity and to a lesser extent the radial size of the filaments are found to decrease as the plasma current is increased at constant density and input power. The results obtained in this paper on the dependence of the average filament dynamics on plasma current are consistent with the idea that the filaments are responsible for determining the particle profiles at the divertor.