On influences of long-range fluctuations on transport in Large Helical Device plasmas

Itoh, K.; Itoh, Sanae I.; Inagaki, S.; Kobayashi, Tatsuya; Fujisawa, A.; Nagashima, Yoshihiko; Oldenbürger, S.; Ida, K.; Tokuzawa, T.; Nagayama, Y.; Kawahata, K.; Yamada, H.

doi:10.1088/0741-3335/54/9/095016

Cited by 18 publications

(20 citation statements)

References 28 publications

(75 reference statements)

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“…For the global fluctuation (with k a 1 ⊥ − ) in LHD [26], the condition 1) is easily satisfied with the estimate of δP/δp ~ P/p. The nonlinear energy exchange between micro-fluctuations and this mode was found to be substantial [27]. The effect of heating on transport is observable in the present experimental cases.…”

Section: Immediate Influence Of Heating On Turbulence and Turbulent T...supporting

confidence: 52%

“…In experiments, the abrupt change of heat flux at the switch-on of the heating occurs in the region where the power absorption is absent [4,5], implying the roles of the meso-and macrofluctuations. Longer-wavelength fluctuations were observed in ECH plasmas on the LHD [26,27]). The hysteresis relation in figure 2 has at least two processes, and can offset the A-dependence of gyro-Bohm-like diffusivity.…”

Section: Hydrogen Isotope Effect On Transportmentioning

confidence: 98%

“…Second, the jump in the hysteresis of gradient-fluctuation relation is more apparent for the longerwavelength fluctuations [1]. The role of longer-wavelength fluctuations in ECH plasmas has been studied experimentally [1,26,27].…”

Section: Immediate Influence Of Heating On Turbulence and Turbulent T...mentioning

confidence: 99%

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Transport hysteresis of core plasma, isotope effect, and H-mode physics

Itoh

Inagaki

2016

Nucl. Fusion

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This article assesses the understanding of and impact by the hysteresis in transport relation. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both edge barrier and core plasmas. The theoretical approaches to understanding the direct influence of heating power on turbulent transport are addressed. Based on this new theoretical framework, the ‘isotope effect’ of plasma confinement time is discussed. A trial explanation is given for this unresolved mystery in plasma confinement. The advanced data analysis method to research the hysteresis in gradient-flux relation is explained.

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Section: Immediate Influence Of Heating On Turbulence and Turbulent T...supporting

confidence: 52%

Section: Hydrogen Isotope Effect On Transportmentioning

confidence: 98%

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Transport hysteresis of core plasma, isotope effect, and H-mode physics

Itoh

Inagaki

2016

Nucl. Fusion

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“…In this sense, one of the important experimental observations is the long range correlation fluctuation in the Large Helical Device (LHD). 21,22 In this observation, the low frequency electron temperature fluctuation is found to have a long radial correlation length. A nonlinear coupling with micro-scale turbulence and macro-scale low frequency fluctuation is clearly identified.…”

Section: Introductionmentioning

confidence: 64%

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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“…5 Recently, it has been widely recognized that the nonlinear coupling with the fluctuations plays important roles in plasma transport. 6 Therefore, it is necessary to consider the nonlinear interactions with the ETG mode and the other fluctuations in order to understand clearly the mechanism of the ETG mode-induced transport. In particular, the importance of the coupling of the ETG mode with poloidally localized large-scale fluctuations, not zonal flows, has been pointed out in toroidal plasmas.…”

mentioning

confidence: 99%

Ion scale nonlinear interaction triggered by disparate scale electron temperature gradient mode

et al. 2015

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We have observed that the disparate scale nonlinear interactions between the high-frequency ($0.4 MHz) electron temperature gradient (ETG) mode and the ion-scale low-frequency fluctuations ($kHz) were enhanced when the amplitude of the ETG mode exceeded a certain threshold. The dynamics of nonlinear coupling between the ETG mode and the drift wave (DW) mode has already been reported [C. Moon, T. Kaneko, and R. Hatakeyama, Phys. Rev. Lett. (2013)]. Here, we have newly observed that another low-frequency fluctuation with f ' 3.6 kHz, i.e., the flute mode, was enhanced, corresponding to the saturation of the DW mode growth. Specifically, the bicoherence between the flute mode and the DW mode reaches a significant level when the rT e /T e strength exceeded 0.54 cm À1 . Thus, it is shown that the ETG mode energy was transferred to the DW mode, and then the energy was ultimately transferred to the flute mode, which was triggered by the disparate scale nonlinear interactions between the ETG and ion-scale low-frequency modes. V C 2015 AIP Publishing LLC. [http://dx.There is strong experimental evidence that the anomalous heat transports are attributed to electron temperature gradient (ETG) driven fluctuations (ETG mode) in magnetically confined plasmas. 1-4 However, the physical mechanism of the ETG mode-induced anomalous transport has not been fully clarified yet because the experimental observations of the ETG mode are limited due to device configurations and are based on the conventional transport process models. 5 Recently, it has been widely recognized that the nonlinear coupling with the fluctuations plays important roles in plasma transport. 6 Therefore, it is necessary to consider the nonlinear interactions with the ETG mode and the other fluctuations in order to understand clearly the mechanism of the ETG mode-induced transport. In particular, the importance of the coupling of the ETG mode with poloidally localized large-scale fluctuations, not zonal flows, has been pointed out in toroidal plasmas. 7,8 In order to understand the evolution of the ETG mode in toroidal plasmas, such a nonlinear interaction between the ETG mode and large-scale fluctuations must be studied in detail. For this purpose, an experiment on the ETG mode in the linear device plasma may provide essential information, even though the ETG mode in the slab cylindrical plasma is not identical to the toroidal ETG mode.For decades, low-frequency fluctuations, such as the drift wave (DW) mode, the flute mode, and others, have been considered to be the main cause of plasma transport. These fluctuations have been well investigated and reported. 5,9 Furthermore, it has been reported that nonlinear couplings of the ETG mode with disparate scale fluctuations 7,8 drive the meso-scale structures such as zonal flows and streamers. 10 Thus, we investigated the nonlinear phenomena of the ETG mode by precisely controlling the ETG in linear magnetized plasmas in order to clearly understand the mechanism of disparate scale nonlinear interactions in the ETG mode...

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On influences of long-range fluctuations on transport in Large Helical Device plasmas

Cited by 18 publications

References 28 publications

Transport hysteresis of core plasma, isotope effect, and H-mode physics

Transport hysteresis of core plasma, isotope effect, and H-mode physics

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

Ion scale nonlinear interaction triggered by disparate scale electron temperature gradient mode

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