The I-mode confinement regime at ASDEX Upgrade: global properties and characterization of strongly intermittent density fluctuations

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

doi:10.1088/0741-3335/59/1/014004

Cited by 47 publications

(112 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The bursts exhibit a solitary-shape and last for about 2-10 µs [5,6]. It has been shown that these bursts are connected with the WCM [5,6]. Most importantly, the intermittent events show up in the divertor several tens of microseconds later than observed with the Doppler reflectometer (DR) in the confined region at a radial position close to the minimum radial electric field [6].…”

Section: Fig 2: Comparison Of Turbulence Amplitude Behavior In (A) Lmentioning

confidence: 96%

“…The presented discharge is in the upper-single null configuration, where the ion ∇B-drift is directed away from the X-point providing the necessary high power threshold for H-mode access. Details on discharge parameters including background profiles can be found in [4,5,6].…”

Section: Fig 1: (A) Spectrum Of Density Fluctuations From Hopping Rementioning

confidence: 99%

“…While the background density turbulence level is reduced compared to the L-mode level, the I-mode in AUG exhibits strong intermittent density bursts causing a heavy-tail probability distribution function [5,6]. The bursts exhibit a solitary-shape and last for about 2-10 µs [5,6]. It has been shown that these bursts are connected with the WCM [5,6].…”

Section: Fig 2: Comparison Of Turbulence Amplitude Behavior In (A) Lmentioning

confidence: 99%

“…In the present contribution the turbulence characteristics of I-mode plasmas in ASDEX Upgrade (AUG) have been studied in detail. Two prominent features, the weakly coherent mode (WCM) [4] and the appearance of strongly intermittent density bursts [5,6] as well as their connection are highlighted. Recent progress on confinement properties of I-mode plasmas in AUG can be found in [2,6].…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade

et al. 2017

View full text Add to dashboard Cite

The I-mode is an improved confinement regime of tokamak plasmas operating in the unfavourable ion ∇B-drift direction combining H-mode-like energy confinement with L-mode-like particle and impurity transport r1s. To qualify the I-mode as an operating scenario for ITER threshold and accessibility studies r2s also on a multimachine basis r3s are needed. Even if the I-mode might not be considered as a promising scenario for ITER, studies of turbulence in I-mode may offer a better understanding of the physics of the interaction of energy and particle transport barriers in general. The mechanism which selectively reduces only one of the transport channels is not understood. In the present contribution the turbulence characteristics of I-mode plasmas in ASDEX-Upgrade (AUG) have been studied in detail. In AUG the WCM appear at frequencies around 100 kHz with a width of a few 10 kHz r4s. The GAM advects the WCM and leads to the broadening through the Doppler effect r4s. In AUG magnetic fluctuations already present in L-mode close to the WCM frequency are amplified during the I-mode. Using the measured background profiles the gyrokinetic eigenvalue solver LIGKA is used to determine the kinetic continuum branches of the GAM and the geodesic Alfvénic mode (GAlf). The frequency of the magnetic fluctuations close to the WCM frequency coincides with the GAlf frequency r4s. Comparisons with the Mirnov coils show the characteristic toroidal and poloidal mode numbers of the GAlf of zero and one, respectively r4s. The origin of the WCM lies in the intermittent events, which exhibit a wavelet-like temporal structure where the characteristic frequency coincides with the centre-of-mass frequency of the WCM r5s. Possible generation scenarios for the bursts are discussed. The nonlinear interaction between GAM, WCM and the bursts will be discussed based on a detailed bispectral analysis of nonlocal interactions in frequency space of the experimental data. The importance of the solitary events for a selective density transport remains an open issue.Published as a journal article in Nuclear Fusion http://iopscience.iop.org/article/Abstract:Turbulence in the I-mode confinement regime of ASDEX Upgrade exhibits beside strong geodesic acoustic mode (GAM) activity two prominent features, the weakly coherent mode (WCM) and strongly intermittent solitary density perturbations. The nonlinear interaction between these structures is studied in detail by means of a conditional averaged waveletbicoherence analysis. The wavelet analysis reveals that the WCM appears as these density bursts. The GAM is coupled to all frequency scales of the velocity fluctuations via a modulational instability. The WCM is broadened through the Doppler effect by the GAM flow. The WCM shows coupling to higher frequencies prior to the bursts indicating a wavesteepening-like process.

show abstract

Section: Fig 2: Comparison Of Turbulence Amplitude Behavior In (A) Lmentioning

confidence: 96%

Section: Fig 1: (A) Spectrum Of Density Fluctuations From Hopping Rementioning

confidence: 99%

Section: Fig 2: Comparison Of Turbulence Amplitude Behavior In (A) Lmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade

et al. 2017

View full text Add to dashboard Cite

show abstract

“…The I-mode was originally observed as an energy confinement improved mode in 1990s [2]; currently, it has been widely investigated in Alcator C-Mod [3,4,5,6,7,8,9,10], AUG [11,12,13,14,15,16], and DIII-D [17]. In unfavorable configurations [18], the L-mode to I-mode transition occurs when the heating power exceeds a certain threshold [19], and an edge energy transport barrier [7] is constructed accompanied with the weak coherent mode (WCM) [13,8,9,10,17] at the steepest temperature gradient region.…”

Section: Introductionmentioning

confidence: 99%

I-mode investigation on the Experimental Advanced Superconducting Tokamak

et al. 2019

View full text Add to dashboard Cite

By analyzing large quantities of discharges in the unfavorable ion B ×∇B drift direction, the I-mode operation has been confirmed in EAST tokamak. During the L-mode to I-mode transition, the energy confinement has a prominent improvement by the formation of a high-temperature edge pedestal, while the particle confinement remains almost identical to that in the L-mode. Similar with the I-mode observation on other devices, the E r profiles obtained by the eight-channel Doppler backscattering system (DBS8)[1] show a deeper edge E r well in the I-mode than that in the L-mode. And a weak coherent mode (WCM) with the frequency range of 40-150 kHz is observed at the edge plasma with the radial extend of about 2-3 cm. WCM could be observed in both density fluctuation and radial electric field fluctuation, and the bicoherence analyses showed significant couplings between WCM and high frequency turbulence, implying that the E r fluctuation and the caused flow shear from WCM should play an important role during I-mode. In addition, a low-frequency oscillation with a frequency range of 5-10 kHz is always accompanied with WCM, where GAM intensity is decreased or disappeared. Many evidences show that the a low-frequency oscillation may be a arXiv:1902.04750v3 [physics.plasm-ph]

show abstract

Actuator management development on ASDEX-Upgrade

Kudláček

Treutterer

Janky

et al. 2019

Fusion Engineering and Design

View full text Add to dashboard Cite

In future tokamak devices, the control system will have to handle several control goals simultaneously with a limited number of actuators in long and high performance discharges. One of the critical roles of the future control systems will be the management of actuators, which would assign the most convenient available actuators primarily to the control goals of the highest importance at the time. Such a system would consist of a discharge program defining the experiment, a discharge supervisor making automatic high level decisions in real time and a component handling the actuators at a lower level: The virtual actuator, which is a software object responsible for distributing the controller commands to a set of selected actuators. This paper describes the implementation of a virtual actuator for all 8 gyrotrons of ASDEX-Upgrade. We also describe the intended use of the virtual actuator for three experiments: β control using ECRH, a disruption avoidance strategy, and electron temperature profile control. The paper also gives an overview of future actuator management developments at ASDEX-Upgrade: extension to all heating sources, inclusion of mirrors for ECRH, and intelligent real time distribution of the actuators between the control goals.

show abstract

The I-mode confinement regime at ASDEX Upgrade: global properties and characterization of strongly intermittent density fluctuations

Cited by 47 publications

References 39 publications

Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade

Turbulence characteristics of the I-mode confinement regime in ASDEX Upgrade

I-mode investigation on the Experimental Advanced Superconducting Tokamak

Actuator management development on ASDEX-Upgrade

Contact Info

Product

Resources

About