Ion heat transport studies in JET

Mantica, P.; Angioni, C.; Baiocchi, B.; Baruzzo, M.; Beurskens, M.; Bizarro, João P. S.; Budny, R.; Buratti, P.; Casati, A.; Challis, C.; Citrin, J.; Colyer, Greg; Crisanti, F.; Figueiredo, A.; Frassinetti, L.; Giroud, C.; Hawkes, N.; Hobirk, J.; Joffrin, E.; Johnson, T.; Lerche, E.; Migliano, P.; Naulin, V.; Peeters, A. G.; Rewoldt, G.; Ryter, F.; Salmi, A.; Sartori, R.; Sozzi, C.; Staebler, G. M.; Strintzi, D.; Tala, T.; Tsalas, M.; Eester, D. Van; Versloot, T. W.; Vries, P. C. de; Weiland, Jan

doi:10.1088/0741-3335/53/12/124033

Cited by 27 publications

(98 citation statements)

References 50 publications

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“…We note that the dependence of this optimum value of u ′ on q/ǫ is not as strong as the dependence of the optimum value of γ E on q/ǫ (clearly this must be so because u ′ = (q/ǫ)γ E ). In a device with an optimised value of q/ǫ, a near maximum critical temperature gradient would be achievable for u ′ > ∼ 5, shears comparable to those observed in experiment [3,16,17].…”

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confidence: 66%

Zero-Turbulence Manifold in a Toroidal Plasma

et al. 2012

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Sheared toroidal flows can cause bifurcations to zero-turbulent-transport states in tokamak plasmas. The maximum temperature gradients that can be reached are limited by subcritical turbulence driven by the parallel velocity gradient. Here it is shown that q/ǫ (magnetic field pitch/inverse aspect ratio) is a critical control parameter for sheared tokamak turbulence. By reducing q/ǫ, far higher temperature gradients can be achieved without triggering turbulence, in some instances comparable to those found experimentally in transport barriers. The zero-turbulence manifold is mapped out, in the zero-magnetic-shear limit, over the parameter space (γE, q/ǫ, R/LT ), where γE is the perpendicular flow shear and R/LT is the normalised inverse temperature gradient scale. The extent to which it can be constructed from linear theory is discussed.

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confidence: 66%

Zero-Turbulence Manifold in a Toroidal Plasma

et al. 2012

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“…Additional observations made in Refs. [24,25,26] pertinent to this work are as follows: at low rotation at ρ = 0.33, the observed stiffness level is higher than the gyrokinetic simulation predictions; furthermore, the observed ITG threshold is lower than the non-linear gyrokinetic prediction, questioning the manifestation of the Dimits shift [27] predicted by non-linear simulations.…”

Section: Introductionmentioning

confidence: 85%

Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment

et al. 2014

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Abstract. Recent experimental observations at JET show evidence of reduced ion temperature profile stiffness, hypothesised to be due to concomitant low magnetic shear (ŝ) and significant toroidal rotational flow shear. Non-linear gyrokinetic simulations are performed, aiming to investigate the physical mechanism behind the observations. A comprehensive set of simulations are carried out, comparing the impact on the ion heat flux of various parameters that differ within the data-set. These parameters include q,ŝ, rotation, effect of rotation on the magnetohydrodynamic (MHD) equilibrium, R/L n , β e , Z ef f , and the fast particle content. The effect of toroidal flow shear itself is not predicted by the simulations to lead to a significant reduction in ion heat flux, due both to an insufficient magnitude of flow shear and significant parallel velocity gradient destabilisation. It is however found that non-linear electromagnetic effects due to both thermal and fast-particle pressure gradients, even at low β e , can significantly reduce the profile stiffness. A total of five discharges are examined, at both inner and outer radii. For all cases studied, the simulated and experimental ion heat flux values agree within reasonable variations of input parameters around the experimental uncertainties.PACS numbers: 52.30. Gz, 52.35.Ra, 52.55.Fa, 52.65.Tt Ion temp. profile stiffness: non-lin. gyrokinetic simu. and comparison with exp.

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“…[7,8,28]. Of particular interest is the magnetic shear (ŝ) dependence, motivated by the observation of increased destiffening at low- s [18]. In figure 1 a β scan is shown for various levels of s, whereŝ = 0.7 is the nominal value for the discharge.…”

Section: Parametrization Of Em-stabilizationmentioning

confidence: 99%

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

Citrin

García

Görler

et al. 2014

Plasma Phys. Control. Fusion

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The impact of electromagnetic stabilization and flow shear stabilization on ITG turbulence is investigated. Analysis of a low-β JET L-mode discharge illustrates the relation between ITG stabilization, and proximity to the electromagnetic instability threshold. This threshold is reduced by suprathermal pressure gradients, highlighting the effectiveness of fast ions in ITG stabilization. Extensive linear and nonlinear gyrokinetic simulations are then carried out for the high-β JET hybrid discharge 75225, at two separate locations at inner and outer radii. It is found that at the inner radius, nonlinear electromagnetic stabilization is dominant, and is critical for achieving simulated heat fluxes in agreement with the experiment. The enhancement of this effect by suprathermal pressure also remains significant. It is also found that flow shear stabilization is not effective at the inner radii. However, at outer radii the situation is reversed. Electromagnetic stabilization is negligible while the flow shear stabilization is significant. These results constitute the high-β generalization of comparable observations found at low-β at JET. This is encouraging for the extrapolation of electromagnetic ITG stabilization to future devices. An estimation of the impact of this effect on the ITER hybrid scenario leads to a 20% fusion power improvement.

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Ion heat transport studies in JET

Cited by 27 publications

References 50 publications

Zero-Turbulence Manifold in a Toroidal Plasma

Zero-Turbulence Manifold in a Toroidal Plasma

Ion temperature profile stiffness: non-linear gyrokinetic simulations and comparison with experiment

Electromagnetic stabilization of tokamak microturbulence in a high-βregime

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