Long-lived coupled peeling ballooning modes preceding ELMs on JET

Thun, C. Perez von; Frassinetti, L.; Horváth, L.; Saarelma, S.; Meneses, L.; Luna, E. de la; Beurskens, M.; Boom, J.; Flanagan, J.; Hillesheim, J. C.; Maggi, C. F.; Pamela, S.; Solano, E.R.; Contributors, Jet

doi:10.1088/1741-4326/ab0031

Cited by 11 publications

(17 citation statements)

References 92 publications

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“…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.…”

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

confidence: 78%

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: An Overview Of the Micro-instabilities In These Pulsesmentioning

confidence: 78%

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

et al. 2022

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“…An example of the ELM precursors from the present datasets can be seen in figure 18. Figure 18 shows the frequency versus the time of the detected perturbations for shot 97039, using the analysis method described in [38]. The colours denote the toroidal mode number of the observed perturbations.…”

Section: Results Of Larger Datasetmentioning

confidence: 99%

“…We should highlight that when the analysis was technically feasible, but no ELM precursors were observed, we cannot exclude that toroidal mode number was too high to be resolved by the diagnostic. It should be noted that these precursors in JET typically grows on the timescales of milliseconds which is more typical of resistive timescales than the timescales of ideal MHD as shown, for example, in reference [38,39].…”

Section: Results Of Larger Datasetmentioning

confidence: 99%

Effect of resistivity on the pedestal MHD stability in JET

Nyström

Frassinetti²,

Saarelma³

et al. 2022

Nucl. Fusion

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The ELM triggering mechanism in tokamaks is not yet fully understood. For example, in the JET tokamak with ITER-like wall (commonly called JET-ILW), the ELMs are sometimes triggered before the ideal peeling-ballooning boundary is reached. This typically occurs for shots with high input power and high gas rate. The discrepancy between model and experiment has in previous works been clearly correlated with the relative shift between the electron temperature and density pedestals. The discrepancy has also been correlated with the resistivity in the middle-bottom of the pedestal. The present work shows that resistive MHD can have a significant impact on the peeling-ballooning stability of JET pedestals. The inclusion of resistivity removes the correlation between the discrepancy from the peeling-balloning stability and the relative shift (the difference between the position of the electron temperature and density pedestals) and significantly improves the agreement between peeling-balloning model and experimental results. The work also shows that the key parameter is the resistivity at the pedestal bottom, near the separatrix, while the resistivity near the middle/top of the pedestal has a negligible effect on the peeling-balloning stability of JET plasmas.

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“…The model assumes that the pedestal evolves till the PB stability boundary is reached and a Type I ELM is triggered. Depending on several parameters, for example collisionality and triangularity, the instabilities can be either a peeling mode, a ballooning mode or a coupled PB modes (see [83] for a recent work on coupled PB modes in JET).…”

Section: Pb Stability Analysismentioning

confidence: 99%

Pedestal structure, stability and scalings in JET-ILW: the EUROfusion JET-ILW pedestal database

et al. 2020

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The EUROfusion JET-ILW pedestal database is described, with emphasis on three main issues. First, the technical aspects are introduced, including a description of the data selection, the datasets, the diagnostics used, the experimental and theoretical methods implemented and the main definitions. Second, the JET-ILW pedestal structure and stability are described. In particular, the work describes the links between the engineering parameters (power, gas and divertor configuration) and the disagreement with the peeling-ballooning (PB) model implemented with ideal MHD equations. Specifically, the work clarifies why the JET-ILW pedestal tends to be far from the PB boundary at high gas and high power, showing that a universal threshold in power and gas cannot be found but that the relative shift (the distance between the position of the pedestal density and of the pedestal temperature) plays a key role. These links are then used to achieve an empirical explanation of the behavior of the JET-ILW pedestal pressure with gas, power and divertor configuration. Third, the pedestal database is used to revise the scaling law of the pedestal stored energy. The work shows a reasonable agreement with the earlier Cordey scaling in terms of plasma current and triangularity dependence, but highlights some differences in terms of power and isotope mass dependence.

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Long-lived coupled peeling ballooning modes preceding ELMs on JET

Cited by 11 publications

References 92 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

Effect of resistivity on the pedestal MHD stability in JET

Pedestal structure, stability and scalings in JET-ILW: the EUROfusion JET-ILW pedestal database

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