Determination of filament parameters on the spherical tokamak Globus-M2 using Doppler backscattering

In high confinement mode (H-mode) in the tokamak Globus-M2, the development of edge-localized modes (ELMs) is accompanied by the appearance of filament structures. Using the Doppler backscattering method allowed to determine the parameters of the filaments during ELMs triggered by and independent from saw-tooth crashes. It was shown that the number of filaments observed during ELMs synchronized with saw-tooth crashes is greater and the area of their observation is wider. The filament velocity during all observed ELM types on Globus-M2 is higher than was the case on the Globus-M tokamak. Filaments that developed immediately before an ELM burst are characterized by smaller amplitudes and velocities. Two diagnostics, Doppler backscattering and poloidal correlation Doppler reflectometry, were used to determine the poloidal velocity of such filaments and the results demonstrated that the velocity values obtained had similar values, which may indicate linear backscattering taking place off these filaments.