Speaker
Viktor Bulanin
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P5.1003.pdf
Application of Doppler backscattering for Alfvén mode investigation on
the Globus-M tokamak
V.V. Bulanin1, V.K. Gusev2, G.S. Kurskiev2, V.B. Minaev2, M.I. Patrov2, A.V. Petrov1,
M.A. Petrov1, Yu.V. Petrov2 N.V. Sakharov2, P.B. Shchegolev2, V.V. Solokha2,
A.Yu. Telnova2, S.Yu. Tolstyakov2, A.Yu. Yashin1.
1
Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia
2
Ioffe Institute, St. Petersburg, Russia
The Doppler backscattering method (DBS) was first employed as a tool for the
investigation of Alfvén modes in the inner regions of a tokamak. The experiments were
carried out on the spherical tokamak Globus-M in conditions where previously the toroidal
Alfvén eigenmodes (TAE) were recorded using a Mirnov probe array [1]. The version of
multifrequency DBS diagnostics was used to record simultaneously microwave
backscattering on four major radii. Quadrature detection multifrequency scheme and the
specifics of the use of the DBS method on the spherical tokamak under a large pitch angle
and magnetic shear are described in detail in Ref. [2]. The cut-off positions of incident
microwave radiation covered a range of normalized small radius from ρ = 0.5 to 0.75. The
experiments were carried out in the deuterium plasma on Globus-M with NBI heating under
the following discharge parameters: Ip = 250 kA, ne < 5×1019 m–3, and BT = 0.5 T. The Alfvén
modes were manifested as oscillations of the poloidal plasma velocity, which was
determined by the DBS diagnostics. The spectra of the velocity oscillations reproduce the
magnetic-field fluctuation’s spectra with great accuracy. The most probable reason for the
occurrence of the velocity oscillations is the ExB drift in the alternating electric field of the
Alfvén wave. Based on this assumption, the absolute amplitudes of the radial electric field
and the magnetic field of the Alfvén modes were estimated in the region of their existence.
The multi-frequency DBS approach has made it possible to determine the areas of the
development of Alfvén oscillations with different mode numbers. The data obtained in the
experiment were used to identify the Alfvén modes in the Globus-M tokamak [3].
References:
[1] Petrov Yu. V. et al. 2015 J. PLASMA PHYS 81 515810601
[2] Yashin A.Y. et al. 2015 JINST 10 P10023
[3] Petrov Yu. V. et al. 2018 this conference
