Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas

Happel, T.; Mänz, P.; Ryter, F.; Hennequin, Pascale; Hetzenecker, A.; Guimarãis, L.; Honoré, Cyrille; Stroth, U.; Viezzer, E.

doi:10.1088/0029-5515/56/6/064004

Cited by 35 publications

(66 citation statements)

References 47 publications

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“…Bursts as seen in the intermittent phase of the LCOs are also found between type-I ELMs, and in very fast heating ramps only this bursty type of LCO spikes appear. In addition, they are similar to bursts which have recently been found in Doppler reflectometry data of I-mode discharges (electron B × ∇B-drift towards X-point ) at AUG [44].…”

Section: Lcos At the L-h Transitionsupporting

confidence: 83%

Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions

et al. 2016

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Limit-cycle oscillations (LCOs) close to the power threshold of L-to H-mode transitions are investigated in plasmas of ASDEX Upgrade. During this phase, referred to as I-phase, a strong magnetic activity in the poloidal magnetic fieldḂ θ with an up-down asymmetry is found. In some cases, the regular LCOs during I-phase transition smoothly into a phase with intermittent bursts which have similar properties to type-III edge localised modes (ELMs). Indications of precursors during the intermittent phase as well as in the regular LCO phase point to a common nature of the I-phase and type-III ELMs. The LCO frequency measured in a set of discharges with different plasma currents and magnetic fields scales as f ∼ (B 1/2 t I 3/2 p )/(nT ).

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Section: Lcos At the L-h Transitionsupporting

confidence: 83%

Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions

et al. 2016

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“…This section compares the experimental ion heat flux, Q i (from TRANSP), electron heat flux Q e (from TRANSP), electron temperature fluctuations (from CECE), and perturbative thermal diffusivity, v pert e (see Equation (8), from partial sawteeth), to global (r/a ¼ 0.65 -0.9), nonlinear, ion-scale GYRO simulations. After presenting these comparisons, this section will summarize the conclusions that one can draw from these results.…”

Section: Comparison To Nonlinear Gyro Resultsmentioning

confidence: 99%

“…The operating window is much wider at 5.4 T (C-Mod's standard field), and no I-H transitions have been observed at 8 T, even with full input power. 7 Despite this smaller operating window at a lower magnetic field, I-mode has also been observed on both ASDEX Upgrade 8,9 and DIII-D. 10 The properties of I-mode outlined here make it quite a favorable candidate for an operating regime on future fusion devices, such as ITER or another high field burning plasma experiment. For this reason, it is vital to understand the core transport in I-mode plasmas (both experimentally and with models) and, in doing so, enable accurate predictions for future devices.…”

Section: Introductionmentioning

confidence: 90%

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod

et al. 2017

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New validation of global, nonlinear, ion-scale gyrokinetic simulations (GYRO) is carried out for L- and I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and temperature fluctuations. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale (cross-scale coupling) effects [Howard PoP 2016] may be less important in I-mode than in L-mode. New results presented here, however, show that global, nonlinear, ion-scale GYRO simulations are able to match the experimental ion heat flux, but underpredict electron heat flux (at most radii), electron temperature fluctuations, and perturbative thermal diffusivity in both L- and I-mode. Linear addition of electron heat flux from electron scale runs does not resolve this discrepancy. These results indicate that single-scale simulations do not sufficiently describe the I-mode core transport, and that multi-scale (coupled electron- and ion-scale) transport models are needed. A preliminary investigation with multi-scale TGLF, however, was unable to resolve the discrepancy between ion-scale GYRO and experimental electron heat fluxes and perturbative diffusivity, motivating further work with multi-scale GYRO simulations and a more comprehensive study with multi-scale TGLF.

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“…An example of a v ⊥ profile obtained from AUG discharge #32294 is shown in figure 13a (red line). Here the Bayesian approach (section 2.3) has been applied to obtain v ⊥ and its k ⊥ in the edge region was performed using a Doppler Reflectometer with a movable mirror [33]. The results shown in figure 15 suggest that dependence of v ph (k ⊥ ) is small (∆v ph ≈ 0.35 km/s between k ⊥ = 0-3 cm −1 and k ⊥ = 9-11 cm −1 ).…”

Section: The Perpendicular Velocity Profile From Aug and Effect Of Dementioning

confidence: 99%

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

Prisiazhniuk

Krämer–Flecken

Happel

et al. 2017

Plasma Phys. Control. Fusion

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Abstract. In fusion machines turbulent eddies are expected to be aligned with the direction of the magnetic field lines and to propagate in the perpendicular direction. Time delay measurements of density fluctuations can be used for the calculation of magnetic field pitch angle α and perpendicular velocity v ⊥ profiles. The method is applied to poloidal correlation reflectometry installed at ASDEX Upgrade and TEXTOR, which measure density fluctuations from poloidally and toroidally separated antennas. Validation of the method is achieved by comparison of the perpendicular velocity (composed of the ExB drift and the phase velocity of turbulence v ⊥ = v E×B +v ph ), with Doppler reflectometry measurements, and with neoclassic fluid calculations. An important condition for the application of the method is the presence of turbulence with sufficiently long decorrelation time. It is shown that at the shear layer the decorrelation time is reduced, limiting the application of the method. The magnetic field pitch angle measured by this method shows the expected dependence on the magnetic field, plasma current and radial position. The profile of the pitch angle reproduces the expected shape and values. However, a comparison with the equilibrium reconstruction code cliste suggests an additional inclination of turbulent eddies at the pedestal position (2-3• ). This additional angle decreases towards core and at the edge.

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Turbulence intermittency linked to the weakly coherent mode in ASDEX Upgrade I-mode plasmas

Cited by 35 publications

References 47 publications

Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions

Magnetic structure and frequency scaling of limit-cycle oscillations close to L- to H-mode transitions

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod

Magnetic field pitch angle and perpendicular velocity measurements from multi-point time-delay estimation of poloidal correlation reflectometry

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