Observation of geodesic acoustic modes in the Globus-M spherical Tokamak

Bulanin, V. V.; Wagner, F.; Варфоломеев, В. И.; Gusev, V. K.; Курскиев, Г. С.; Минаев, В. Б.; Патров, М. И.; Petrov, A. V.; Petrov, Yu. V.; Prisyazhnyuk, D. V.; Сахаров, Н. В.; Tolstyakov, S. Yu.; Хромов, Н. А.; Shchegolev, P. B.; Yashin, A. Yu.

doi:10.1134/s106378501405006x

Cited by 17 publications

(9 citation statements)

References 7 publications

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“…GAMs were identified in the spherical tokamak Globus-M [6,7] was discovered as coherent oscillations of perpendicular velocity in 20-35 kHz frequency range provided the backscatter region was located inside the separatrix [8][9][10]. This frequency range was in line with theoretical estimations performed for the conditions of the Globus-M periphery [11].…”

Section: Geodesic Acoustic Modesupporting

confidence: 83%

Recent Doppler backscattering applications in Globus-M tokamak

et al. 2019

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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.

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Section: Geodesic Acoustic Modesupporting

confidence: 83%

Recent Doppler backscattering applications in Globus-M tokamak

et al. 2019

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“…GAMs appeared as quasi-coherent oscillations of the Doppler shift in the 20-30 kHz frequency range. The amplitude of electric-field oscillations in this frequency band reached 3 kV m −1 and significantly exceeded the mean values of the radial electric field [12]. The GAM frequencies measured in deuterium and hydrogen plasmas were found to be in good agreement with the theoretical estimations obtained by kinetic analysis based on finite inverse aspect ratio [9].…”

Section: Geodesic Acoustic Mode Studiessupporting

confidence: 79%

Review of Globus-M spherical tokamak results

et al. 2015

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The first experiments on noninductive current drive (CD) using lower hybrid waves in a spherical tokamak are described. Waves at 2.45 GHz were launched by a 10 waveguide grill with 120° phase shift between neighbouring waveguides. The experimental results for a novel poloidal slowing-down scheme are described. The CD efficiency is found to be somewhat larger than that predicted theoretically whilst at the same time being somewhat less than that for standard tokamak lower hybrid CD. Geodesic acoustic modes (GAM) have been discovered in Globus-M. GAMs are localized 2-3 cm inside the separatrix. The GAM frequency agrees with theory. The mode structures of plasma density and magnetic field oscillation at the GAM frequency have been studied. Fast particle confinement during neutral beam injection has been investigated and numerically simulated. Alfvén instabilities excited by fast particles were detected by a toroidal Mirnov probe array. Their excitation conditions are discussed and the dynamics of fast ion losses induced by Alfvén eigenmodes is presented. Preliminary experiments on the isotopic effect influence on global confinement in the ohmic Nuclear Fusion

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“…GAMs were studied on the spherical tokamak Globus-M using microwave Doppler backscattering also known as Doppler reflectometry (DR) [35]. Similarly to TUMAN-3M [21] and other tokamaks [36], GAMs were observed only in the L-mode of the discharge, and disappeared after the L-H-transition.…”

Section: Gam Structure On Globus-m Tokamakmentioning

confidence: 99%

Fusion Research in Ioffe Institute

et al. 2015

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In this paper we present the fusion related activities of the Plasma Physics Division at the Ioffe Institute. The first experiments on lower hybrid current drive (LHCD) in a spherical tokamak performed at the Globus-M tokamak (R = 0.36 m, a = 0.24 m, B t = 0.4 T, I p = 200 kA) with a novel poloidally oriented grill resulted in an RF driven current of up to 30 kA at (100 kW, 2.5 GHz), exceeding the modelling predictions. At the FT-2 tokamak (R = 0.56 m, a = 0.08 m, B t = 3 T, I p = 30 kA) experiments with a traditional toroidally oriented grill revealed no strong dependence of the LHCD density limit on the H/D ratio in spite of LH resonance densities differing by a factor of 3. Microwave Doppler reflectometry (DR) at the Globus-M, and DR and heavy ion beam probe measurements at the tokamak TUMAN-3M (R = 0.53 m, a = 0.24 m, B t = 1.0 T, I p = 190 kA) demonstrated geodesic acoustic mode (GAM) suppression at the L to H transition. Observations at FT-2 using Doppler Enhanced Scattering showed that the GAM amplitude is anti-correlated both spatially and temporally to the drift turbulence level and electron thermal diffusivity. For the first time turbulence amplitude modulation at the GAM frequency was found both experimentally and in global gyrokinetic modelling. A model of the L-H transition is proposed based on this effect. The loss mechanisms of energetic ions' (EI) were investigated in the neutral beam injection (NBI) experiments on Globus-M and TUMAN-3M. Empirical scaling of the 2.45 MeV DD neutron rate for the two devices shows a strong dependence on toroidal field B 1.29 t and plasma current I 1.34 p justifying the B t and I p increase by a factor of 2.5 for the proposed upgrade of Globus-M. Bursts of ∼1 MHz Alfvenic type oscillations correlating with sawtooth crashes were observed in ohmic TUMAN-3M discharges. The possibility of low threshold parametric excitation of Bernstein and upper hybrid waves trapped in drift-wave eddies resulting in anomalous absorption in electron cyclotron resonance heating (ECRH) experiments in toroidal plasmas was identified theoretically. A novel method of radial correlation Doppler reflectometry is shown to be capable of measuring the turbulence wave-number spectrum in realistic 2D geometry. On the progress in design and fabrication of three diagnostics for ITER developed in the Ioffe institute is reported: neutral particle analysis, divertor Thomson scattering and gamma spectroscopy.

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Observation of geodesic acoustic modes in the Globus-M spherical Tokamak

Cited by 17 publications

References 7 publications

Recent Doppler backscattering applications in Globus-M tokamak

Recent Doppler backscattering applications in Globus-M tokamak

Review of Globus-M spherical tokamak results

Fusion Research in Ioffe Institute

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