Geodesic acoustic mode investigation in the spherical Globus-M tokamak using multi-diagnostic approach

Abstract

Owing to the active researches of intermediate regime which is known as limit cycle oscillation (LCO) regime, it is important to investigate oscillations of velocity of zonal flows, plasma density and magnetic field simultaneously. The geodesic acoustic mode (GAM) investigations using multi-diagnostic were carried out on the spherical tokamak Globus-M (R = 0.36 m, a = 0.24 m, Ip = 150 kA, BT = 0.3 T). Variation of GAM intensity showed features of LCO regime. The key implement for researches was a method of Doppler microwave backscattering, or Doppler reflectometry (DR). The diagnostic consisted of two Doppler reflectometers, which were apart in poloidal direction. Oscillations of plasma density at GAM frequencies were investigated using electrostatic probes and detectors of Dα intensity emission, which were detected at different lines of sight. Structure of magnetic field perturbation has been investigated using poloidal and toroidal Mirnov probe arrays. Correlation analysis shown that the structure of ExB velocity oscillations had corresponded to n=0, m=0. The main structure of density fluctuations at GAM frequency had n=0, m=0 mode numbers. Besides the n=0, m=1 component is also presented. The mode structure for magnetic field disturbance was established. To interpret an origin of plasma density global perturbation at GAM frequency plausible model was suggested.

Experimental observations of modes with geodesic acoustic character from the core to the edge in the TCV tokamak

“…In the 2011-2013 TCV campaign [11], GAMs were simultaneously observed as a coherent mode in four different fields: the m = 0Ẽ × B flow, the m = 1 density componentñ, the electron temperature componentT e , as well as the magnetic componentB θ , which was found to have toroidal mode number n = 0 and poloidal mode number dominated by m = 2, consistent with theoretical predictions [16]. The magnetic component of the GAM was also reported from the DIII-D [9], T-10 [12] and Globus-M [17] tokamaks. In the latter case oscillations at the GAM frequency were also observed on the D α emission intensity.…”

“…In addition, GAM oscillations have been observed and characterized on the SOL diagnostics near the strike points in various divertor configurations. This is the first study of its kind, even though oscillations at the edge GAM frequency were occasionally detected before by, e.g., D α measurements in Globus-M [17] and Langmuir probe measurements in Alcator C-Mod [18]. An extensive characterization has been provided in varying divertor geometries.…”

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

“…Poloidal correlation DBS using two microwave schemes with the cut-offs positioned at different poloidal angles (−30° and 45°) of the same minor cross-section was employed in Globus-M to study the poloidal structure of GAMs [32,44]. The zero phase delay between the GAM oscillations in the two simultaneously detected DBS signals was discovered by coherent spectrum analysis of the velocity oscillations, which is presented in Figure 3.…”

“…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].…”

Влияние Низкочастотных Магнитогидродинамических Мод На Развитие Филаментов В Токамаке Глобус-М

“…Для регистрации филаментов использовался метод микроволнового допплеровского обратного рассеяния (ДОР). Метод активно используется для измерения скоростей вращения плазмы и колебаний скоростей вращения в тороидальных системах магнитного удержания [14][15][16][17][18][19][20][21][22][23][24][25]. Возможность регистрации филаментов с помощью метода ДОР была продемонстрирована впервые в работе [26].…”