Studying pedestal characteristics in MAST ELMy regimes in preparation for future spherical tokamaks

Studying pedestal characteristics in MAST ELMy regimes in preparation for future spherical tokamaks

Studying pedestal characteristics in MAST ELMy regimes in preparation for future spherical tokamaks 150 150 UKAEA Opendata
UKAEA-CCFE-PR(23)104

Studying pedestal characteristics in MAST ELMy regimes in preparation for future spherical tokamaks

MAST pedestal data has been analysed, where a pedestal database of 892 shots was obtained, using the new upgraded MAST Thomson Scattering (TS) diagnostic. Various ELM types are discussed, where characteristics and trends of MAST pedestals are shown. The data from the upgraded TS diagnostic confirms pedestal characteristics found in earlier analysis, using previous TS systems. Using the database, calculations of the bootstrap current are obtained using the different analytical formulae (Sauter and Redl), and comparisons are performed. At high collisionality discrepancies between the analytical calculations are found for MAST. The new MAST TS system now spans the full plasma mid-plane, such that direct comparisons between inboard and outboard pedestals can be obtained. When the inboard and outboard pedestals are compared asymmetries in the density pedestal width are found. In order to increase confidence in spherical tokamak pedestal predictions, the assumptions of Europed have been validated for MAST pedestal data. Using the experimental database for type I ELMs in single and double null configurations, a value for the KBM constraint (C) has been obtained. Here, it was found C ∼ 0.145. Using this value, the first spherical tokamak pedestal predictions were performed in Europed and compared to MAST experimental data. The temperature pedestal height was predicted to within 10% error of the experimental value. In addition type II ELMs on MAST are analysed, and stability analysis and parameter scans have been performed using ESSIVE. Similar MHD stability properties are observed for type I and type II ELMs, originating from the mixed ELM regimes, and it is therefore difficult to distinguish these ELMs using the ideal MHD codes.

Collection:
Journals
Journal:
Plasma Physics and Controlled Fusion
Publisher:
IOP (Institute of Physics)