Experimental study of the relationship between micro-turbulence and magnetohydrodynamics on the HT-7 tokamak

Sun, P. J.; Li, Y D; Li, Q; Zhang, W Y; Zhang, X D; Hu, Liqun; Li, J

doi:10.1088/0031-8949/85/05/055504

Cited by 5 publications

(5 citation statements)

References 20 publications

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“…Recently, experimental observation of the interactions between turbulent fluctuations and magnetic islands have been extensively studied [64][65][66][67][68][69][70][71][72][73]. The spatial correlation between turbulent electron temperature fluctuations and magnetic islands in KSTAR is reported [67].…”

Section: Introductionmentioning

confidence: 99%

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Multi-scale interactions between turbulence and magnetic islands and parity mixture—a review

Ishizawa

Kishimoto

Nakamura

2019

Plasma Phys. Control. Fusion

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This paper presents a review of multi-scale interactions between small-scale turbulence and large scale magnetic islands. In finite beta plasmas, zonal flows are relatively weak, and thus another electromagnetic coherent structure formation such as magnetic islands becomes important for regulating turbulence. In multi-scale interactions, large-scale modes dominate turbulent fluctuations even when the growth rate of the large-scale mode is much smaller than small-scale modes. On the other hand, small-scale modes influence large-scale modes when the large-scale modes are stable/marginally stable. Thus, the multi-scale interactions are categorized according to the stability of tearing mode (TM), which drives large-scale magnetic islands. When the TM is unstable, wide magnetic islands are produced, and as a result of the multi-scale interactions, the turbulent transport is significantly enhanced inside the separatrix of the island, because large-scale stable modes are excited by mutual interactions between turbulence and the island. On the other hand, a steep temperature gradient is formed around the separatrix of the island, which is consistent with zonal flow shear appearing at the separatrix. When the TM is stable/marginally stable, turbulence drives and sustains magnetic islands of width equal to multiples of the Larmor radius. This excitation of islands by turbulence can be related to the seed island formation of neo-classical TMs. The parity of fluctuations plays crucial role in the multi-scale nonlinear interactions, because pure twisting parity mode does not satisfy the nonlinear fluid/gyrokinetic equations. Magnetic islands belongs to the tearing parity mode and drift-wave instabilities normally belong to the twisting parity mode, and each parity is conserved in the linear growth of the instability. However, when the amplitude of the twisting parity mode becomes finite, the nonlinear energy transfer takes place from the twisting parity to tearing parity modes. Through this nonlinear parity mixture, the magnetic islands are produced by the turbulence. The influence of anomalous current drive and polarization current on the multi-scale interactions is discussed as well.

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Section: Introductionmentioning

confidence: 99%

“…The relation between turbulent density fluctuation and a magnetic island in DIII-D is presented [68,69]. The temporal correlations between turbulence and magnetic islands in HL-2A and EAST are investigated [70][71][72][73]. Comparison with numerical simulation results has just started.…”

Section: Introductionmentioning

confidence: 99%

Multi-scale interactions between turbulence and magnetic islands and parity mixture—a review

Ishizawa

Kishimoto

Nakamura

2019

Plasma Phys. Control. Fusion

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“…However, in medium-high frequency (400-1000 kHz), things are quite different: correlation of wavenumber 12 cm −1 is much stronger than before while there is a gradual increase in the correlation of wavenumber 22 cm −1 spectrogram. Bursts in Mirnov coil signals are observed in the discharge at 9.0 s. According to Sun et al 2012, electron density fluctuations obviously increase during sawtooth activities or Mirnov activities [26,27]. Fluctuation of the Mirnov signal could lead to a change in the structure of the confinement mode, which could be proved by the increase in the medium-high frequency of the k=22 cm −1 spectrogram since 9.0 s. The investigation of the confinement structure with the analysis of cross-correlation spectrogram might be justified then.…”

Section: Existence Of An Improved Confinement Modementioning

confidence: 94%

Dynamic evolution of microturbulence with an improved confinement mode in the ramp-down phase of plasma current on EAST

Bi¹,

Li²,

Wu³

et al. 2019

Plasma Phys. Control. Fusion

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Micro-instabilities are often invoked to account for the anomalous transport of energy and particles in fusion plasmas, whose origin and contributions to anomalous transport remain uncertain. The dynamic features of the microturbulence in the plasma core and the gradient region are investigated simultaneously by a poloidal CO2 laser coherent scattering diagnostic system on the experimental advanced superconducting tokamak (EAST). In 2018, an improved confinement mode characterized by a peaked density profile is observed in the current ramp-down phase with no auxiliary heating, which has rarely been studied. The experimental result suggests that the gradual shut off of the LHW heating might trigger the mode transition. The transition is accompanied with a great suppression of microturbulence and significant change in the cross-correlation spectrum. A possible mechanism for the suppression could be ascribed to the increasing E ⃑ × B ⃑ shear flow. These results could shed light on the understanding of the nonlinear mechanism of confinement mode transition on EAST.

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“…Microturbulence was measured with collective scattering of electromagnetic waves, which is a powerful technique capable of providing the spectral power of density fluctuations [18,19]. The CO 2 laser collective scattering system has always been employed in the HT-7 tokamak, providing measurement of microturbulence with the wave vectors in the poloidal direction [20,21]. In the campaign of 2012, the tangential CO 2 laser collective scattering system [28] was first installed on the EAST tokamak, as shown in figure 1(a).…”

Section: Methodsmentioning

confidence: 99%

Characterization of core microturbulence in L-mode and H-mode regimes on the EAST superconducting tokamak

Cao¹,

Li²,

Li³

et al. 2015

Phys. Scr.

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The core microturbulence ( ≈ − r a / 0.4 0.5, ρ − ⊥ k ~1.5 4.3 s ) provided by a tangential CO 2 laser collective scattering system on the EAST tokamak, in low (L) and high (H) confinement mode regimes respectively, are presented. We report the change of core microturbulence characteristics from L-mode to H-mode: firstly, the spectrograms of the core microturbulence show the redistribution of microturbulence in the frequency domain after the L-H transition; secondly, the time evolution of the integrated spectral power displays that the amplitude of the core microturbulence in H-mode is much larger than that in L-mode; thirdly, the cross-correlation time-frequency spectrum analysis indicates that the structural characteristics of the core microturbulence in L-mode and H-mode are very different. These results suggest that both the amplitude and the structural characteristics of the core microturbulence change significantly from L-mode to H-mode, although the spatial extent of the transport barrier in H-mode is at the edge, which could be closely related to the changes of the profiles of basic plasma parameters.

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Experimental study of the relationship between micro-turbulence and magnetohydrodynamics on the HT-7 tokamak

Cited by 5 publications

References 20 publications

Multi-scale interactions between turbulence and magnetic islands and parity mixture—a review

Multi-scale interactions between turbulence and magnetic islands and parity mixture—a review

Dynamic evolution of microturbulence with an improved confinement mode in the ramp-down phase of plasma current on EAST

Characterization of core microturbulence in L-mode and H-mode regimes on the EAST superconducting tokamak

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