L-Mode and Inter-ELM Divertor Particle and Heat Flux Width Scaling on MAST

TL;DR

This study measures and analyzes particle and heat flux decay lengths in MAST tokamak discharges, revealing dependencies on plasma parameters and differences between L-mode and H-mode conditions.

Contribution

It provides new parametric dependencies of decay lengths and estimates diffusion coefficients for particle and heat fluxes in MAST divertor plasmas.

Findings

Decay lengths depend on separatrix electron density and plasma current.

Diffusion coefficients range from 1 to 7 m²/s and are lower in H-mode.

Exponential decay lengths are mapped to the midplane for analysis.

Abstract

The distribution of particles and power to plasma-facing components is of key importance in the design of next-generation fusion devices. Power and particle decay lengths have been measured in a number of MAST L-mode and H-mode discharges in order to determine their parametric dependencies, by fitting power and particle flux profiles measured by divertor Langmuir probes, to a convolution of an exponential decay and a Gaussian function. In all discharges analysed, it is found that exponential decay lengths mapped to the midplane are mostly dependent on separatrix electron density and plasma current (or parallel connection length). The widths of the convolved Gaussian functions have been used to derive an approximate diffusion coefficient, which is found to vary from 1m2/s to 7m2/s, and is systematically lower in H-mode compared with L-mode.