Speaker
Vitaly Zenin
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P2.1090.pdf
The study of long range electric potential correlation on the GAM
frequency on the T-10 tokamak
V.N. Zenin1, 2, M.A. Drabinskij1, 2, L.G. Eliseev1, S.A. Grashin1, P.O. Khabanov1, 2,
N.K. Kharchev1, A.V. Melnikov1, 3
1
NRC Kurchatov Institute, Moscow, Russia
2
Moscow Institute of Physics and Technology, Dolgoprudny, Russia
3
National Research Nuclear University MEPhI, Moscow, Russia
In the recent years there has been significant interest to Geodesic Acoustic Modes
(GAM). GAMs, being the high-frequency counterpart of zonal flows, can be a possible
mechanism of the turbulence self-regulations. It has been shown theoretically that GAMs
manifest themselves as oscillations of plasma electric potential with m = n = 0 (and can
weakly be seen on density with m = 1, n = 0).
GAMs have been studied with two main diagnostics: Langmuir probes and Heavy ion
beam probing (HIBP), a unique method for direct measurement of the electric potential in the
hot plasma core. Diagnostics are separated by half of torus of the T-10 tokamak (R= 1.5 m,
a= 0.3 m, B < 2.5 T).
This work is dedicated to simultaneous measurements of plasma potential oscillations
at GAM frequencies in different locations and studying of their correlation properties. It was
found that coherency between signals of two diagnostics is up to 0.8 that is unexpectedly
high for such a large distance between them, half of torus in toroidal and about π in poloidal
direction. Such coherency appears when Langmuir probes were located at about ρ = 0.95.
Also, the phase shift between potentials measured with two diagnostics has been obtained.
The value of coherency decreases with increasing in radial distance between HIBP
sample volume and probes position. The phase shift between electric potential oscillation
measured with HIBP and measured with Langmuir probes in the GAM frequency range was
negative (about - 1.5 – 2.2 rad). Its value increases with increasing in radial distance between
points of observation of two diagnostics. We assume that phase shift in toroidal and poloidal
directions is equal to zero because m = n = 0 for GAM. Since phase shift is negative plasma
potential wave propagates outwards. The magnitude of its velocity changes from ~ 2 km/s
(Δr ≈ 3 cm) to 7 km/s (Δr ≈ 11 cm).
This work was funded by Russian Science Foundation, Project 14-22-00193.
