Studies of the pedestal structure and inter-ELM pedestal evolution in JET with the ITER-like wall

Maggi, C. F.; Frassinetti, L.; Horváth, L.; Lunniss, A.; Saarelma, S.; Wilson, H. R.; Flanagan, J.; Leyland, Matthew; Lupelli, I.; Pamela, S.; Urano, H.; Garzotti, L.; Lerche, E.; Nunes, I.; Rimini, F.

doi:10.1088/1741-4326/aa7e8e

Cited by 34 publications

(74 citation statements)

References 30 publications

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“…On the other hand, variations in D have been experimentally observed in several machines with D≈0.084 in Alcator C-mod [50] to D≈0.1 in AUG [62] and JT-60U [63,64,65] and D≈0.06-0.13 TCV [29]. Specifically for JET-ILW, a large variation has been observed, with D≈0.06-0.13 [53,59]. So a large part of JET-ILW pedestal width cannot be predicted with the standard EPED1 model.…”

Section: The Pb Model and The Eped Frameworkmentioning

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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Section: The Pb Model and The Eped Frameworkmentioning

confidence: 99%

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

et al. 2020

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“…Two term scalings, separating core and pedestal thermal confinement in the H-mode, have been reported to have a very strong pedestal scaling τ E,ped ∝ A 0.96 and a weak negative dependence of the plasma core confinement τ E,core ∝ A −0.16 (Cordey et al 1999). Here, τ E,ped = W ped /P loss , with W ped = 1.5(n e ped T e ped + n i ped T i ped )V top where subscript ped refers to the values at the pedestal top, which is typically 1-3 cm inward from the LCFS in JET (Maggi et al 2017), V top ≈ V is the volume inside the flux surface defined by the pedestal top and V the total plasma volume. The core confinement time is defined as τ E,core = τ E − τ E,ped .…”

Section: Introductionmentioning

confidence: 99%

Isotope dependence of energy, momentum and particle confinement in tokamaks

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Maggi²,

Oberparleiter³

et al. 2020

J. Plasma Phys.

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The isotope dependence of plasma transport will have a significant impact on the performance of future D-T experiments in JET and ITER and eventually on the fusion gain and economics of future reactors. In preparation for future D-T operation on JET, dedicated experiments and comprehensive transport analyses were performed in H, D and H-D mixed plasmas. The analysis of the data has demonstrated an unexpectedly strong and favourable dependence of the global confinement of energy, momentum and particles in ELMy H-mode plasmas on the atomic mass of the main ion species, the energy confinement time scaling as ${\tau _E}\sim {A^{0.5}}$ (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045; JET Team, Nucl. Fusion, vol. 39, 1999, pp. 1227–1244), i.e. opposite to the expectations based only on local gyro-Bohm (GB) scaling, ${\tau _E}\sim {A^{ - 0.5}}$ , and stronger than in the commonly used H-mode scaling for the energy confinement (Saibene et al., Nucl. Fusion, vol. 39, 1999, 1133; ITER Physics Basis, Nucl. Fusion, vol. 39, 1999, 2175). The scaling of momentum transport and particle confinement with isotope mass is very similar to that of energy transport. Nonlinear local GENE gyrokinetic analysis shows that the observed anti-GB heat flux is accounted for if collisions, E × B shear and plasma dilution with low-Z impurities (9Be) are included in the analysis (E and B are, respectively the electric and magnetic fields). For L-mode plasmas a weaker positive isotope scaling ${\tau _E}\sim {A^{0.14}}$ has been found in JET (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045), similar to ITER97-L scaling (Kaye et al., Nucl. Fusion, vol. 37, 1997, 1303). Flux-driven quasi-linear gyrofluid calculations using JETTO-TGLF in L-mode show that local GB scaling is not followed when stiff transport (as is generally the case for ion temperature gradient modes) is combined with an imposed boundary condition taken from the experiment, in this case predicting no isotope dependence. A dimensionless identity plasma pair in hydrogen and deuterium L-mode plasmas has demonstrated scale invariance, confirming that core transport physics is governed, as expected, by the 4 dimensionless parameters ρ*, ν*, β, q (normalised ion Larmor radius, collisionality, plasma pressure and safety factor) consistently with global quasi-linear gyrokinetic TGLF calculations (Maggi et al., Nucl. Fusion, vol. 59, 2019, 076028). We compare findings in JET with those in different devices and discuss the possible reasons for the different isotope scalings reported from different devices. The diversity of observations suggests that the differences may result not only from differences affecting the core, e.g. heating schemes, but are to a large part due to differences in device-specific edge and wall conditions, pointing to the importance of better understanding and controlling pedestal and edge processes.

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“…[32,[46][47][48]). On JET, the EPED model works quite well at low gas fuelling, but not so well at high gas rates [49][50][51][52][53][54][55]. The search for the PB modes has also motivated the study of electromagnetic fluctuation activity arising near the plasma periphery prior to ELMs.…”

Section: Introductionmentioning

confidence: 99%

Long-lived coupled peeling ballooning modes preceding ELMs on JET

et al. 2019

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In some JET discharges, type-I Edge Localised Modes (ELMs) are preceded by a class of low frequency oscillations [Perez et al Nucl. Fusion 44 (2004) 609]. While in many cases the ELM is triggered during the growth phase of this oscillation, it is also observed that this type of oscillations can saturate and last for several tens of ms until an ELM occurs. In order to identify the nature of these modes, a wide pre-ELM oscillation database including detailed pedestal profile information has been assembled and analysed in terms of MHD stability parameters. The existence domain of these pre-ELM oscillations and the statistical distribution of toroidal mode numbers (n) up to n = 16 has been mapped in ballooning alpha (α ball) and either edge current density (J edge) or pedestal collisionality (ν * ee,ped) coordinates and compared to linear MHD stability predictions. The pre-ELM oscillations are reliably observed when the J/α ratio is high enough for the pedestal to access the coupled peelingballooning (PB) domain (aka stability nose). Reversely, when the pedestal is found to be in or near the high-n ballooning domain (which is at low J/α ratio), ELMs are usually triggered promptly, i.e. with no detectable pre-ELM oscillations, or with pre-ELM oscillations only observable on ECE whose n appears to be too high to be resolved by the magnetics. Individual discharges can sometimes exhibit a fairly wide range of pre-ELM mode numbers, but for a wider database the statistical n-number domains are found to be well ordered along the J-α stability boundary and behave as expected from PB theory: the higher the J/α ratio, the lower the mode's measured n tends to be. Within the measurement uncertainties, the measured n is usually found to be compatible with the most unstable n predicted by the linear stability code MISHKA1. These results confirm the earlier hypothesis that these modes are coupled peelingballooning modes, and extend and generalise to higher mode numbers the work by Huysmans

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Studies of the pedestal structure and inter-ELM pedestal evolution in JET with the ITER-like wall

Cited by 34 publications

References 30 publications

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

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

Isotope dependence of energy, momentum and particle confinement in tokamaks

Long-lived coupled peeling ballooning modes preceding ELMs on JET

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