Inter-ELM pedestal localized fluctuations in tokamaks: Summary of multi-machine observations

Laggner, F. M.; Diallo, A.; Cavedon, M.; Kolemen, Egemen

doi:10.1016/j.nme.2019.02.030

Cited by 31 publications

(33 citation statements)

References 83 publications

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“…The success of the perturbative approach applied here also implies a possibility for the expansion of dynamic turbulence identification to other unexplained tokamak regimes. Similar instability markers have been reported on a wide variety of machines and scenarios 6,32 , but the underlying physics remains largely undetermined. The analysis presented here offers a new mechanism to uncover explanations for these observations, potentially enabling a comprehensive perturbative study of experimental transport signatures in tokamak devices.…”

Section: Discussion and Outlooksupporting

confidence: 66%

“…Remarkably, this profile-based calculation exactly matches the mode chirping behavior seen in fast magnetic fluctuation measurements, as shown in figure 2(c). Through this theoretically-motivated analysis, we thus explain the distinctive up-chirping behavior observed in magnetic spectrograms 6,25,[30][31][32] as follows: The recovery of density and temperature gradients after an ELM 32 introduces periodic growth into the ω e * profile described by equation 1. MTMs, being locked at a particular rational q surface, will simultaneously experience a local increase in ∇T e and ω e * .…”

Section: Time-dependent Mtm Identificationmentioning

confidence: 99%

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Perturbative Determination of Plasma Microinstabilities in Tokamaks

Nelson,

Laggner,

Diallo

et al. 2021

Preprint

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Recently, theoretical analysis has identified plasma microinstabilities as the primary mechanism responsible for anomalous heat transport in tokamaks. In particular, the microtearing mode (MTM) has been credited with the production of intense electron heat fluxes, most notably through a thin self-organized boundary layer called the pedestal. Here we exploit a novel, time-dependent analysis to compile explicit experimental evidence that MTMs are active in the pedestal region. The expected frequency of pedestal MTMs, calculated as a function of time from plasma profile measurements, is shown in a dedicated experiment to be in excellent agreement with observed magnetic turbulence fluctuations. Further, fast perturbations of the plasma equilibrium are introduced to decouple the instability drive and resonant location, providing a compelling validation of the analytical model. This analysis offers strong evidence of edge MTMs, validating the existing theoretical work and highlighting the important role of MTMs in regulating electron heat flow in tokamaks.

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Section: Discussion and Outlooksupporting

confidence: 66%

Section: Time-dependent Mtm Identificationmentioning

confidence: 99%

Perturbative Determination of Plasma Microinstabilities in Tokamaks

Nelson,

Laggner,

Diallo

et al. 2021

Preprint

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“…Related gyrokinetic modeling will be reported in [20]. Collectively, these results suggest that MTMs are likely responsible for many of the most prominent magnetic fluctuations observed in the pedestal of tokamaks (see references [18,[21][22][23][24][25][26]).…”

Section: Introductionmentioning

confidence: 55%

Identifying the microtearing modes in the pedestal of DIII-D H-modes using gyrokinetic simulations

Hassan¹,

Hatch²,

Halfmoon³

et al. 2021

Nucl. Fusion

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Recent evidence points toward the microtearing mode (MTM) as an important fluctuation in the H-mode pedestal for anomalous electron heat transport. A study of the instabilities in the pedestal region carried out using gyrokinetic simulations to model an ELMy H-mode DIII-D discharge (USN configuration, 1.4 MA plasma current, and 3 MW heating power) is presented. The simulations produce MTMs, identified by predominantly electromagnetic heat flux, small particle flux, and a substantial degree of tearing parity. The magnetic spectrogram from Mirnov coils exhibits three distinct frequency bands---two narrow bands at lower frequency ($\sim$35-55 kHz and $\sim$70-105 kHz) and a broader band at higher frequency ($\sim$300-500 kHz). Global linear GENE simulations produce MTMs that are centered at the peak of the $\omega_*$ profile and correspond closely with the bands in the spectrogram. The three distinctive frequency bands can be understood from the basic physical mechanisms underlying the instabilities. For example (i) instability of certain toroidal mode numbers (n) is controlled by the alignment of their rational surfaces with the peak in the $\omega^*$ profile, and (ii) MTM instabilities in the lower n bands are the conventional collisional slab MTM, whereas the higher n band depends on curvature drive. While many features of the modes can be captured with the local approximation, a global treatment is necessary to quantitatively reproduce the detailed band gaps of the low-n fluctuations. Notably, the transport signatures of the MTM are consistent with careful edge modeling by SOLPS.

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“…the pedestal height is not always limited by MHD events [7], such as in the case of the QH mode [8,9], whose pedestal is argued to be limited by transport physics. Also, even for type-I ELMy H-mode [10], where the EPED model applies, for most (>80%) of the time during an Edge Localized Mode (ELM) cycle, the pedestal structure is likely to be determined by transport dynamics [11,12], highlighting the importance of understanding transport physics in the pedestal.…”

Section: Introductionmentioning

confidence: 99%

Gyrokinetic simulation of pedestal degradation correlated with enhanced magnetic turbulence in a DIII-D ELMy H-mode discharge

Jian,

Chen,

Holland

et al. 2024

Plasma Phys. Control. Fusion

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Gyrokinetic simulation of a dedicated pedestal density ramping-up discharge on DIII-D can reproduce the enhancement of magnetic turbulence in the pedestal, which is identified to be caused by micro-tearing modes (MTM). Increase of MTM amplitude results in higher electron thermal diffusivity, consistent with experimentally observed lower electron temperature gradient and degraded pedestal height. Gyrokinetic simulation identifies the major cause of MTM enhancement to be the increase of collisionality, which has a significant impact on the MTM intensity and is beyond the description of any (quasi-)linear theory.

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Inter-ELM pedestal localized fluctuations in tokamaks: Summary of multi-machine observations

Cited by 31 publications

References 83 publications

Perturbative Determination of Plasma Microinstabilities in Tokamaks

Perturbative Determination of Plasma Microinstabilities in Tokamaks

Identifying the microtearing modes in the pedestal of DIII-D H-modes using gyrokinetic simulations

Gyrokinetic simulation of pedestal degradation correlated with enhanced magnetic turbulence in a DIII-D ELMy H-mode discharge

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