How is turbulence intensity determined by macroscopic variables in a toroidal plasma?

Inagaki, S.; Tokuzawa, T.; Tamura, N.; Itoh, Sanae–I.; Kobayashi, Tatsuya; Ida, K.; Shimozuma, Τ.; Kubo, S.; Tanaka, Kaoru; Ido, T.; Shimizu, A.; Takahashi, Hayato; Kasuya, Naohiro; Nagayama, Y.; Kawahata, K.; Sudo, S.; Yamada, H.; Fujisawa, A.; Itoh, K.

doi:10.1088/0029-5515/53/11/113006

Cited by 72 publications

(135 citation statements)

References 36 publications

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“…In addition, the studies of relation between heat/particle/momentum flux and temperature/density/flow gradient are shown that the flux is not necessarily determined by the local plasma parameters. [10][11][12][13][14][15][16][17] In cold pulse propagation experiments, for example, the core plasma temperature shows the fast change after the edge cooling. [18][19][20] The change of temperature is much faster than the expected value from the diffusive process in a thermal transport.…”

Section: Introductionmentioning

confidence: 99%

Observation of multi-scale turbulence and non-local transport in LHD plasmas

et al. 2014

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We have studied two types of spatio-temporal turbulence dynamics in plasmas in the Large Helical Device, based on turbulence measurements with high spatial and temporal resolution. Applying conditional ensemble-averaging to a plasma with Edge-Localized Modes (ELMs), fast radial inward propagation of a micro-scale turbulence front is observed just after ELM event, and the propagation speed is evaluated as ∼100 m/s. A self-organized radial electric field structure is observed in an electrode biasing experiment, and it is found to realize a multi-valued state. The curvature of the radial electric field is found to play an important role for turbulence reduction.

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Section: Introductionmentioning

confidence: 99%

Observation of multi-scale turbulence and non-local transport in LHD plasmas

et al. 2014

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“…This new method directly measures the gradient-flux relation by studying the temperature response with respect to modulations of the electron cyclotron heating (ECH) power. Using this method, hysteresis in the gradient-flux relation was observed in LHD plasmas [1,2]. Because heat flux is a multivalued function of gradient, the temperature perturbation dynamics are far from a simple diffusive response with constant diffusion coefficient.…”

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confidence: 99%

Higher Harmonics in the Perturbative Transport Study in TJ-II ECH Plasma

Inagaki

Itoh

et al. 2014

Plasma and Fusion Research

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We analyzed the higher harmonics of temperature perturbation in the modulated electron cyclotron heating experiment on TJ-II plasma. The higher harmonics (e.g., 5th harmonic) exhibited significantly weaker decay in amplitude as they propagated in radius as compared with the prediction by diffusive model. The change in the time derivative of temperature at the onset (and turning-off) of the heating power propagates in radius with very little temporal smoothening. Recently, a new method for analyzing anomalous transport in magnetically confined plasmas was developed. This new method directly measures the gradient-flux relation by studying the temperature response with respect to modulations of the electron cyclotron heating (ECH) power. Using this method, hysteresis in the gradient-flux relation was observed in LHD plasmas [1,2]. Because heat flux is a multivalued function of gradient, the temperature perturbation dynamics are far from a simple diffusive response with constant diffusion coefficient. Therefore, higher harmonics can exhibit smaller or larger spatial damping rates in comparison with the diffusive response. To observe the violation of the simple diffusive relation q = −nχ∇T with homogeneous χ, measuring the higher harmonics of temperature perturbation in the heating modulation experiment was proposed [3]. In this rapid communication, we report the application of the abovementioned method to the modulated electron cyclotron heating (MECH) experiment on the TJ-II [4].The power modulation experiment with line-averaged values around 0.5 × 10 19 m −3 was performed on a lowdensity plasma using continuous on-axis heating with 250 kW and modulated 50 kW (square waveform, 50% duty cycle) microwave beams. The modulation frequency of ECH ( f mod ) is 180 Hz, mostly absorbed in the central core r/a ≤ 0.3 (plasma radius a = 0.2 m), as determined in previous heat wave propagation experiments [5]. The electron temperature profile was measured at ten points in the high-field side region of 0.0 < r/a < 0.9 using an ECE author's e-mail: inagaki@riam.kyushu-u.ac.jp heterodyne radiometer with a time resolution of 10 µs [6]. The comparison with the T e measured using a He beam indicates that ECE can measure T e even at the edge [7]. We applied the conditional averaging technique [1]. In this procedure, the ECH turn-on time (t on ) is detected in each period and temporal evolutions of the electron temperature for time intervals of −3 ms < t − t on < 3 ms were extracted; the extracted signals were averaged over 25 modulations. Post averaging, the noise level significantly decreased. Figure 1 illustrates the power spectrum of the conditionally averaged temperature perturbation and Fig. 1 Power spectrum of the conditionally averaged temperature perturbation (black solid line) and that calculated from the raw signal (red dashed line). Higher harmonics up to the 5th are presented. The black dashed line is for visual aid.

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“…We apply the telegraph equation to the heat pulse propagation caused by periodic modulation of the heating power. The result is compared qualitatively with that from an LHD experiment [1]. However, the model cannot explain the phase relation in the hysteresis between the temperature gradient and the heat flux.…”

Section: Introductionmentioning

confidence: 93%

“…Recently, limitations have been recognized in conventional diffusive models of transport, which employ Fick's law to relate the temperature gradient and heat flux [1,2]. In electron cyclotron heating (ECH) power modulation experiments in the large helical device (LHD), turbulent flux is changed before changes in local gradients occur [1].…”

Section: Introductionmentioning

confidence: 99%

“…In electron cyclotron heating (ECH) power modulation experiments in the large helical device (LHD), turbulent flux is changed before changes in local gradients occur [1]. In generalizing the relation between the temperature gradient and turbulent heat flux, one approach is to consider the finite time of relaxation (delay time) of turbulence in response to the changes in global plasma parameters; this approach is used in the K-ε model (or K-model) [3,4].…”

Section: Introductionmentioning

confidence: 99%

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Test of the Telegraph Equation for Transport Dynamics in Plasma

Inagaki

Itoh

et al. 2015

Plasma and Fusion Research

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We have tested the telegraph equation for transport dynamics in magnetized plasma by comparing its results with experimental observations in the Large Helical Device [S. Inagaki et al., Nucl. Fusion 53, 113006 (2013)]. The telegraph equation includes a finite relaxation time for turbulence intensity in response to the changes in global plasma parameters. This model was applied to nondiffusive radial heat pulse propagation under the periodic modulation of the heating power. The model showed some success in reproducing the amplitudes of higher harmonics. However, the phase relation between the temperature gradient and heat flux was opposite to that in experimental observations.

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How is turbulence intensity determined by macroscopic variables in a toroidal plasma?

Cited by 72 publications

References 36 publications

Observation of multi-scale turbulence and non-local transport in LHD plasmas

Observation of multi-scale turbulence and non-local transport in LHD plasmas

Higher Harmonics in the Perturbative Transport Study in TJ-II ECH Plasma

Test of the Telegraph Equation for Transport Dynamics in Plasma

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