Experimental and numerical characterisation of the turbulence in the Scrape-Off Layer of MAST

TL;DR

This study combines numerical simulations and experimental measurements to analyze turbulence in the Scrape-Off Layer of MAST, validating models and highlighting the importance of temperature fluctuations for accurate plasma diagnostics.

Contribution

The paper provides a detailed comparison between simulated and experimental turbulence data in MAST, confirming the interchange model's validity and emphasizing the need for temperature fluctuation measurements.

Findings

Good agreement between simulations and experiments in average profiles and PDFs.

The interchange model effectively captures key turbulence features.

Temperature fluctuations significantly impact the accuracy of plasma potential and velocity measurements.

Abstract

Numerical simulations of interchange turbulence in the Scrape-Off Layer are performed in a regime relevant for a specific L-mode MAST (Mega Ampere Spherical Tokamak) discharge. Such a discharge was diagnosed with a reciprocating arm equipped with a Gundestrup probe. A detailed comparison of the average and statistical properties of the simulated and experimental ion saturation current is performed. Good agreement is found in the time averaged radial profile, in the probability distribution functions (PDFs) and in qualitative features of the signals such as the shape, duration and separation of burst events. These results confirm the validity of the simple interchange model used and help to identify where it can be improved. Finally, the simulated data are used to assess the importance of the temperature fluctuations on plasma potential and radial velocity measurements acquired with Langmuir probes. It is shown that the correlation between the actual plasma quantities and the signal of the synthetic diagnostics is poor, suggesting that accurate measurements of the temperature fluctuations are needed in order to obtain reliable estimates of the perpendicular fluxes.