First results of turbulence investigation on Globus-M2 using radial correlation Doppler reflectometry

The first results of investigation of the turbulence structure using Doppler backscattering (DBS) on the Globus-M2 tokamak are presented. A one-channel DBS system with a variable probing frequency within the 18-26 GHz range was installed to investigate the edge plasma at normalized minor radii ρ = 0.9 – 1.1. Radial correlation Doppler reflectometry was used to study the changes in turbulence eddies after the LH transition. Correlation analysis was applied to the phase derivative of complex IQ signals of the DBS diagnostic as it contains information about the poloidal plasma rotation velocity. In L-mode the radial correlation length Lr is estimated to be 3 cm and after transition to H-mode reduces to approximately 2 cm. Gyrokinetic modelling in a linear local approximation using code GENE indicates that the instability with positive growth rates at the normalized minor radius ρ = 0.75 in L-mode and H-mode on Globus-M2 was the ion temperature gradient (ITG) mode.