Recent Doppler backscattering applications in Globus-M tokamak

Abstract

A: Recently, a four-frequency Doppler backscattering (DBS) system was installed on the Globus-M tokamak. In addition to the classical DBS application for determining the mean plasma rotational velocities, DBS was used for the investigation of different plasma oscillatory processes in the spherical Globus-M tokamak. Application of various DBS data processing allowed us to reveal and investigate plasma oscillations, such as geodesic acoustic mode, limit cycle oscillations and Alfvén modes. It has been shown that DBS also allows registering filament like structures, which manifest as quasi-coherent oscillations in signals of various DBS channels. The multi-frequency DBS system makes it possible to localize plasma oscillations, their poloidal and radial sizes and mode structure. The main results of the DBS application for the study of these oscillations are presented. A comparison of the DBS data with the data of other diagnostics is also given. K: Nuclear instruments and methods for hot plasma diagnostics; Plasma diagnosticsprobes 1Corresponding author.

Review of Advanced Implementation of Doppler Backscattering Method in Globus-M

“…The radial scale of the observed flow is estimated to be 4 cm [42,46]. This scale is close to the radial wavelength of the zonal flows [41].…”

“…The GAM frequency was also investigated in different locations and it was determined that no significant change of its values was present. Experiments with a four frequency DBS scheme confirmed the narrow localization of GAM [42]. Only the peripheral DBS channel could register GAM oscillations near the normalized minor radius 0.95, whereas the other channels did not detect oscillations exceeding the background level at the GAM frequency.…”

“…It was shown that an SMBI pulse can reduce the Doppler shift frequency, which corresponds to the flattening of the electric field. In a series of experiments on the EAST tokamak using two separate DBS systems, one for the Q-band (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(46)(47)(48)(49)(50) and the other for the V-band (50-75 GHz), Doppler shifted signals were obtained and radial profiles of perpendicular velocities were computed for the L-and H-mode [15]. In the Globus-M2 tokamak, the first results of the Doppler backscattering diagnostics during a discharge with the L-H transition show that the transition process is linked to the deformation of the poloidal rotation velocity profile [16].…”

Modelling of Backscattering off Filaments Using the Code IPF-FD3D for the Interpretation of Doppler Backscattering Data

“…Filament characteristics have been studied extensively over the years using various diagnostic techniques [ 7 ]. One such diagnostic technique (unconventional though it may be for this purpose) is the Doppler backscattering (DBS) method [ 8 ], which was initially employed at the spherical tokamak Globus-M [ 9 , 10 , 11 , 12 , 13 ] and later the ASDEX Upgrade tokamak [ 14 ] for the purpose of studying filaments. It has been observed that the DBS signal reacts to backscattering from filaments.…”

Doppler backscattering systems on the Globus-M2 tokamak

“…For example, it had been used for the first time to investigate the properties of Alfven eigenmodes such as amplitude, location and their dependence on the plasma parameters which proved a fruitful venture [15], however the possibility to detect these instabilities using DBS was demonstrated earlier in work [17]. The localization and detection of different phenomena on the Globus-M tokamak was determined [18]. Unfortunately, due to the limitations of the DBS system itself not everything could be investigated or analysed.…”