Pedestal confinement and stability in JET-ILW ELMy H-modes

Maggi, C. F.; Saarelma, S.; Casson, F. J.; Challis, C.; Luna, E. de la; Frassinetti, L.; Giroud, C.; Joffrin, E.; Simpson, J.; Beurskens, M.; Chapman, I. T.; Hobirk, J.; Leyland, Matthew; Lomas, P. J.; Lowry, C.; Nunes, I.; Rimini, F.; Sips, A. C. C.; Urano, H.

doi:10.1088/0029-5515/55/11/113031

Cited by 90 publications

(266 citation statements)

References 33 publications

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“…Several results from different experimental machines are consistent with this scaling [18,[51][52][53][54][55][56]. Inconsistencies with the KBM constraint have been observed in NSTX [46,57], AUG [54] and JET-ILW [58].…”

Section: Introductionsupporting

confidence: 57%

“…Good confinement with H 98 ≈ 1.0 has been recently recovered by moving the outer strike point on the divertor corner allowing operation at a lower density [12,17,18].…”

Section: Confinement Factor and Normalized Confinement Scalingmentioning

confidence: 99%

“…In the core, the reduced collisionality led to an increased density peaking and the temperature profile stiffness led to an increased core temperature. These two effects led to an increased core-stored energy [18]. However, it was not possible to extract conclusive information on the role of collisionality in confinement and in pedestal stability because both the normalized plasma pressure (β) and the normalized ion Larmor radius (ρ * ) were not constant.…”

Section: Introductionmentioning

confidence: 99%

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Global and pedestal confinement and pedestal structure in dimensionless collisionality scans of low-triangularity H-mode plasmas in JET-ILW

et al. 2016

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A dimensionless collisionality scan in low-triangularity plasmas in the Joint European Torus with the ITER-like wall (JET-ILW) has been performed. The increase of the normalized energy confinement (defined as the ratio between thermal energy confinement and Bohm confinement time) with decreasing collisionality is observed. Moreover, at low collisionality, a confinement factor H 98 , comparable to JET-C, is achieved. At high collisionality, the low normalized confinement is related to a degraded pedestal stability and a reduction in the density-profile peaking.The increase of normalized energy confinement is due to both an increase in the pedestal and in the core regions. The improvement in the pedestal is related to the increase of the stability. The improvement in the core is driven by (i) the core temperature increase via the temperature-profile stiffness and by (ii) the density-peaking increase driven by the low collisionality.Pedestal stability analysis performed with the ELITE (edge-localized instabilities in tokamak equilibria) code has a reasonable qualitative agreement with the experimental results. An improvement of the pedestal stability with decreasing collisionality is observed. The improvement is ascribed to the reduction of the pedestal width, the increase of the bootstrap current and the reduction of the relative shift between the positions of the pedestal density and pedestal temperature.The EPED1 model predictions for the pedestal pressure height are qualitatively well correlated with the experimental results. Quantitatively, EPED1 overestimates the

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Section: Introductionsupporting

confidence: 57%

“…Good confinement with H 98 ≈ 1.0 has been recently recovered by moving the outer strike point on the divertor corner allowing operation at a lower density [12,17,18].…”

Section: Confinement Factor and Normalized Confinement Scalingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Global and pedestal confinement and pedestal structure in dimensionless collisionality scans of low-triangularity H-mode plasmas in JET-ILW

et al. 2016

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“…The pedestal current density is calculated according to the Sauter's bootstrap cur rent model [20]. For high ν * ped discharges, it has been shown in [26,27] that the Sauter formula [20] overestimates the bootstrap current, however in the present simulations this discrepancy was not accounted for and the Sauter formula was used for every discharge.…”

Section: Simulating Elms In Jetmentioning

confidence: 70%

Recent progress in the quantitative validation of JOREK simulations of ELMs in JET

et al. 2017

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Future devices like JT-60SA, ITER and DEMO require quantitative predictions of pedestal density and temperature levels, as well as inter-ELM and ELM divertor heat fluxes, in order to improve global confinement capabilities while preventing divertor erosion/melting in the planning of future experiments. Such predictions can be obtained from dedicated pedestal models like EPED, and from non-linear MHD codes like JOREK, for which systematic validation against current experiments is necessary. In this paper, we show progress in the quantitative validation of the JOREK code using JET simulations. Results analyse the impact of diamagnetic terms on the dynamics and size of the ELMs, and evidence is provided that the onset of type-I ELMs is not governed by linear MHD stability alone, but that a nonlinear threshold could be responsible for large MHD events at the plasma edge.

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“…This work reports the results of, perhaps, the very first, first-principles simulations of the H-mode pedestal dynamics that reproduce experimentally observed transport levels. In addition to providing unprecedented insight into the dynamics of the existing H-mode pedestals, such simulations are likely to advance our capabilities towards predictive modeling of future burning plasma devices.This study targets the JET-ILW (ITER-like wall) pedestal [4][5][6], which approaches ITER conditions in two important ways: 1) as the largest tokamak in operation, it most-closely approximates plasma parameters that are dependent on machine size (like ρ * , the ratio of the gyroradius to minor radius), 2) to approximate ITER conditions even better, JET has recently installed an ITERlike wall (ILW) (composed of a tungsten divertor and beryllium chamber). This modification decreases the global performance of discharges by 20-30%, attributable largely to changes in pedestal structure.…”

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confidence: 99%

Microtearing turbulence limiting the JET-ILW pedestal

et al. 2016

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Gyrokinetic simulations identify microtearing modes (MTM) to be the dominant microinstabilities in the JET-ILW (ITER like wall) pedestal. Nonlinear simulations show that MTM-driven turbulence produces the bulk of the transport in the steep gradient region, demonstrating that MTM may be the principal mechanism limiting JET-ILW pedestal evolution. The combination of MTM, electron temperature gradient (ETG), and neoclassical transport reproduces experimental power balance across most of the pedestal. Kinetic ballooning modes are significant only in the local limit and only at low β, far below the experimental operating point. PACS numbers:The tokamak H-mode [1] is defined by a narrow insulating region-the pedestal-at the plasma edge, where turbulence is suppressed and sharp pressure gradients develop. The pedestal is at the center of the most pressing issues facing fusion energy. ITER, for example, must reach a sufficient temperature at the pedestal's inner boundary in order to achieve its fusion power targets [2]. This work reports the results of, perhaps, the very first, first-principles simulations of the H-mode pedestal dynamics that reproduce experimentally observed transport levels. In addition to providing unprecedented insight into the dynamics of the existing H-mode pedestals, such simulations are likely to advance our capabilities towards predictive modeling of future burning plasma devices.This study targets the JET-ILW (ITER-like wall) pedestal [4][5][6], which approaches ITER conditions in two important ways: 1) as the largest tokamak in operation, it most-closely approximates plasma parameters that are dependent on machine size (like ρ * , the ratio of the gyroradius to minor radius), 2) to approximate ITER conditions even better, JET has recently installed an ITERlike wall (ILW) (composed of a tungsten divertor and beryllium chamber). This modification decreases the global performance of discharges by 20-30%, attributable largely to changes in pedestal structure. In addition to the performance loss, certain observed key properties of the ILW pedestal are inconsistent with predictions of the leading pedestal model (EPED [7,8]).In this work, we elucidate possible mechanisms limiting profile evolution in the JET-ILW discharges. We demonstrate, through simulations using the gyrokinetic code Gene [9,10], that the microtearing mode (MTM) [11][12][13][14] is the dominant instability in the pedestal. Interestingly, the simulations do not find the kinetic ballooning mode (KBM), a basic component of the EPED model, except locally in a narrow region near the separatrix. Most importantly, we determine via nonlinear gyrokinetic simulations that a combination of MTM and electron temperature gradient (ETG) [9,[15][16][17][18] driven turbulence plus the neoclassical flux, produces transport levels closely matching experimental power balance across most of the pedestal, demonstrating the capacity of these mechanisms to limit JET-ILW pedestal evolution.The JET-ILW Pedestal-JET pulse 82585 (described in Ref. [4]) is pa...

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Pedestal confinement and stability in JET-ILW ELMy H-modes

Cited by 90 publications

References 33 publications

Global and pedestal confinement and pedestal structure in dimensionless collisionality scans of low-triangularity H-mode plasmas in JET-ILW

Global and pedestal confinement and pedestal structure in dimensionless collisionality scans of low-triangularity H-mode plasmas in JET-ILW

Recent progress in the quantitative validation of JOREK simulations of ELMs in JET

Microtearing turbulence limiting the JET-ILW pedestal

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