Study of Turbulence in the Globus-M Tokamak Plasma during the Transition to the ELM-free H-mode

Abstract

Here we report the results of the turbulence study in the high-confinement mode (H-mode) with and without edge localized modes (ELMs). The study was performed by the Doppler backscattering (DBS) method on the Globus-M tokamak. Two types of ELMs were observed in the Globus-M tokamak during NBI heating and accordingly, two different transitions to transient ELM-free modes were discovered. It was demonstrated that the transition from the H-mode with ELMs accompanied by small sawtooth oscillations to the ELM-free H-mode is characterized by the drop of the turbulence amplitude near the periphery while the transition in the case of ELMs is accompanied by large sawtooth oscillations, which occur without suppression of peripheral turbulence.