Reduced models for ETG transport in the tokamak pedestal

Hatch, D. R.; Michoski, Craig; Kuang, Da; Chapman-Oplopoiou, B.; Curie, M.; Halfmoon, Michael; Hassan, Ehab; Kotschenreuther, M.; Mahajan, S. M.; Merlo, Gabriele; Pueschel, M. J.; Justin, Walker,; Stephens, C. D.

doi:10.1063/5.0087403

Cited by 19 publications

(29 citation statements)

References 32 publications

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“…Despite this observation, the value of k y ρ s for which the linear growth rate spectrum peaks was determined by η e in all four cases, with higher values of η e leading to lower values of k y ρ s . This is also consistent with the steep gradient nonlinear flux spectra presented here, and is a key component of a new quasilinear model of ETG pedestal turbulence described in [38]. Corresponding nonlinear scans in ω T e and ω n e for the two high power pulses showed similarities with trends in the peak growth rates from linear simulations.…”

Section: Discussionsupporting

confidence: 87%

“…This strongly suggests that it is η e that determines the location of the peaks in the turbulent heat flux spectra shown in the lower panel of figure 7; indeed, the peaks in the lower panel of figure 7 can be ordered from right to left in increasing η e . This distinctive dependence of the spectrum on η e is a key component of a new quasilinear model of ETG pedestal turbulence described in [38]. While the corresponding traces for the other three pulses are not shown, the trend is qualitatively similar.…”

Section: Normalised Temperature and Density Gradient Scansmentioning

confidence: 72%

“…We used the Hager bootstrap current formula for the equilibrium calculation [34] which under predicts the bootstrap current somewhat compared to NEO [35,36] in our high power pulses, but is in good agreement with NEO for the low power pulses [37]. Results from a large database of pedestal ETG simulations [38] (which includes many of the simulations in the present manuscript), show no discernible correlation between the pedestal ETG turbulent heat flux and the magnetic shear ŝ. Therefore, we do not expect the uncertainty in the bootstrap current to impact our work significantly.…”

Section: An Overview Of the Micro-instabilities In These Pulsesmentioning

confidence: 78%

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The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

et al. 2022

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We present the results of GENE gyrokinetic calculations based on a series of JET-ILW type I ELMy H-mode discharges operating with similar experimental inputs but at different levels of power and gas fuelling. We show that turbulence due to electron-temperature-gradient modes (ETGs) produces a significant amount of heat flux in four JET-ILW discharges, and, when combined with Neoclassical simulations, is able to reproduce the experimental heat flux for the two low gas pulses. The simulations plausibly reproduce the high-gas heat fluxes as well, although power balance analysis is complicated by short ELM cycles. By independently varying the normalised temperature gradients ωTe and normalised density gradients ωne around their experimental values, we demonstrate that it is the ratio of these two quantities ηe = ωTe / ωne that determines the location of the peak in the ETG growth rate and heat flux spectra. The heat flux increases rapidly as ηe increases above the experimental point, suggesting that ETGs limit the temperature gradient in these pulses. When quantities are normalised using the minor radius, only increases in ωTe produce appreciable increases in the ETG growth rates, as well as the largest increases in turbulent heat flux which follow scalings similar to that of critical balance theory. However, when the heat flux is normalised to the electron Gyro-Bohm heat flux using the temperature gradient scale length LTe , it follows a linear trend in correspondence with previous work by different authors.

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Section: Discussionsupporting

confidence: 87%

Section: Normalised Temperature and Density Gradient Scansmentioning

confidence: 72%

Section: An Overview Of the Micro-instabilities In These Pulsesmentioning

confidence: 78%

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The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

et al. 2022

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“…Such work currently being undertaken by the IFS group [32], attempting to determine a heat flux scaling to fit a database of nonlinear GENE turbulence simulations of pedestals from a variety of devices, hints that a stiffer scaling with ηe may be a better fit to the gyro-Bohm normalized heat flux data. Of course, it may well be that other turbulent modes are involved in the electron heat transport, e.g.…”

Section: Discussionmentioning

confidence: 99%

Comparing pedestal structure in JET-ILW H-mode plasmas with a model for stiff ETG turbulent heat transport

Field

Chapman-Oplopoiou

Connor

et al. 2023

Phil. Trans. R. Soc. A.

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A predictive model for the electron temperature profile of the H-mode pedestal is described, and its results are compared with the pedestal structure of JET-ILW plasmas. The model is based on a scaling for the gyro-Bohm normalized, turbulent electron heat flux q e / q e , gB resulting from electron temperature gradient (ETG) turbulence, derived from results of nonlinear gyrokinetic (GK) calculations for the steep gradient region. By using the local temperature gradient scale length L T e in the normalization, the dependence of q e / q e , gB on the normalized gradients R / L T e and R / L n e can be represented by a unified scaling with the parameter η e = L n e / L T e , to which the linear stability of ETG turbulence is sensitive when the density gradient is sufficiently steep. For a prescribed density profile, the value of R / L T e determined from this scaling, required to maintain a constant electron heat flux q e across the pedestal, is used to calculate the temperature profile. Reasonable agreement with measurements is found for different cases, the model providing an explanation of the relative widths and shifts of the T e and n e profiles, as well as highlighting the importance of the separatrix boundary conditions. Other cases showing disagreement indicate conditions where other branches of turbulence might dominate. This article is part of a discussion meeting issue ‘H-mode transition and pedestal studies in fusion plasmas’.

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“…In H-mode [1,2] tokamak plasma, electron fluxes can be driven by a rich variety of waves and instabilities covering a large range of temporal and spatial scales making its modeling (in terms of its width and height) challenging. Effectively, several studies on the origin of the electron heat transport in the pedestal region [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21] show that drift-wave, such as the electron-temperature-gradient (ETG) instability, the trapped-electron mode (TEM), and electromagnetic instabilities, such as kinetic-ballooning mode (KBM) and microtearing (MT) modes of interest here, can explain the electron heat transport observed experimentally. These instabilities can develop in the pedestal region, leading to turbulence, which affects the transport and the confinement of heat and particles.…”

Section: Introductionmentioning

confidence: 94%

Linear stability of the JET H-mode pedestal

Hamed

Pueschel

Citrin

et al. 2022

J. Phys.: Conf. Ser.

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The stability of microtearing (MT) in the JET H-mode pedestal is investigated by means of both linear gyrokinetic simulations using the GENE code and a theoretical calculation. In order to determined the role played by MT in tokamak pedestal and to evaluate the role played by physical parameters, on MT destabilization a reduced linear model has been presented and compared with gyrokinetic simulations. The analytical model allows a good prediction of the impact of the different physical parameters, like the collisionality in the pedestal.

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Reduced models for ETG transport in the tokamak pedestal

Cited by 19 publications

References 32 publications

The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

The role of ETG modes in JET–ILW pedestals with varying levels of power and fuelling

Comparing pedestal structure in JET-ILW H-mode plasmas with a model for stiff ETG turbulent heat transport

Linear stability of the JET H-mode pedestal

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