Doppler reflectometer system in the stellarator TJ-II

Happel, T.; Estrada, T.; Blanco, E.; Tribaldos, V.; Cappa, Á.; Bustos, A.

doi:10.1063/1.3160106

Cited by 107 publications

(107 citation statements)

References 22 publications

Supporting

Mentioning

105

Contrasting

Order By: Relevance

“…Since the wave is focussed to the cutoff layer with an optimum beam size [49,59,60], the spectral resolution is optimized and typical values of ∆k ⊥ ≈ 2.0−2.2 cm −1 are obtained, depending on the probing beam frequency f 0 . For more details on the Doppler reflectometer hardware, the reader is referred to Refs.…”

Section: Measurement Techniquementioning

confidence: 99%

Core turbulence behavior moving from ion-temperature-gradient regime towards trapped-electron-mode regime in the ASDEX Upgrade tokamak and comparison with gyrokinetic simulation

et al. 2015

Self Cite

View full text Add to dashboard Cite

Additional electron cyclotron resonance heating (ECRH) is used in an ion-temperature-gradient instability (ITG) dominated regime to increase R/L Te in order to approach the trapped-electron-mode instability (TEM) regime. The radial ECRH deposition location determines to a large degree the effect on R/L Te . Accompanying scale-selective turbulence measurements at perpendicular wavenumbers between k ⊥ = 4 -18 cm −1 (k ⊥ ρ s = 0.7 -4.2) show a pronounced increase of large-scale density fluctuations close to the ECRH radial deposition location at mid-radius, along with a reduction in phase velocity of large-scale density fluctuations. Measurements are compared with results from linear and non-linear flux-matched gyrokinetic (GK) simulations with the gyrokinetic code gene. Linear GK simulations show a reduction of phase velocity, indicating a pronounced change in the character of the dominant instability. Comparing measurement and non-linear GK simulation, as a central result, agreement is obtained in the shape of radial turbulence level profiles. However, the turbulence intensity is increasing with additional heating in the experiment, while gyrokinetic simulations show a decrease.

show abstract

Section: Measurement Techniquementioning

confidence: 99%

Core turbulence behavior moving from ion-temperature-gradient regime towards trapped-electron-mode regime in the ASDEX Upgrade tokamak and comparison with gyrokinetic simulation

et al. 2015

Self Cite

View full text Add to dashboard Cite

show abstract

“…In TJ-II, a Doppler reflectometer is installed [43] which can operate in the whole range of magnetic configurations available, and in different plasma scenarios. A sketch of the system is shown in Fig.…”

Section: Figmentioning

confidence: 99%

“…The employed diagnostic technique is Doppler reflectometry, which is relatively new (∼ 10 years), but used on several tokamaks and stellarators worldwide [38][39][40][41][42][43][44].…”

Section: Introductionmentioning

confidence: 99%

Scale-selective turbulence reduction in H-mode plasmas in the TJ-II stellarator

Happel

Estrada²,

Blanco³

et al. 2011

Physics of Plasmas

Self Cite

View full text Add to dashboard Cite

Wavenumber spectra of density turbulence in L-and H-mode plasmas have been measured in the TJ-II stellarator by means of Doppler reflectometry. A pronounced suppression of the density fluctuation level is observed in H-mode close to the radial position of maximum radial electric field (Er) shear. Furthermore, intermediate scale density turbulence is reduced preferentially. This effect can be interpreted within the framework of vortex stretching feeding energy through Reynolds stress into zonal flows, while shear decorrelation of turbulent structures might not play a central role in TJ-II. Moreover, it is shown that in both L-and H-mode, the phase velocity of density fluctuations does not depend on the structure scale.

show abstract

“…In TJ−II, a two−channel Doppler reflectometer is used that allows the measurement of the radial electric field, E r and density fluctuations at two radial positions simultaneously with good spatial and temporal resolution [17].…”

mentioning

confidence: 99%

Spatiotemporal Structure of the Interaction between Turbulence and Flows at the L-H Transition in a Toroidal Plasma

Estrada¹,

Hidalgo²,

et al. 2011

Self Cite

View full text Add to dashboard Cite

The spatio-temporal behavior of the interaction between turbulence and flows has been studied close to the L−H transition threshold conditions in the edge region (ρ ≥ 0.7) of TJ−II plasmas. The temporal dynamics of the interaction displays an oscillatory behaviour with a characteristic predator−prey relationship. The spatial evolution of this turbulence−flow oscillation−pattern has been measured, for the first time, showing both, radial outward and inward propagation velocities of the turbulence−flow front. The results indicate that the edge shear flow linked to the L−H transition can behave either as a slowing−down, damping mechanism of outward propagating turbulent−flow oscillating structures, or as a source of inward propagating turbulence-flow events.The High confinement mode (H−mode) regime has been extensively studied since its discovery in the AS-DEX tokamak [1]. Although significant progress has been made in describing the transition, the physical mechanism triggering the H-mode has still not been clearly identified. Bifurcation theory models based on the coupling between turbulence and radially sheared E×B flows (sheared flows) describes the Low to High confinement mode transition (L−H transition) passing through an intermediate, oscillatory transient stage [2,3]. These models consist of coupled evolution equations for turbulence, sheared flow and pressure gradient. Using the input power as a control parameter for the pressure gradient, these dynamical systems evolve from L− to H−mode. By increasing the pressure gradient, the instability grows until it is damped by the self-generated sheared flows. The transition occurs when the turbulence driven sheared flow is high enough to overcome the flow damping. As it is discussed in Ref. [3], by including the evolution of zonal flows self-consistently, the critical input power for the transition is lowered. Further studies [4] show that zonal flows are a necessary step for the transition. Zonal flows trigger the transition by regulating the turbulence until the mean shear flow is high enough to suppress turbulence effectively, which in turn subsequently impedes the zonal flow generation. Due to the self-regulation between turbulence and flows, the transition is marked by an oscillatory behavior with a characteristic predator−prey relationship and EAST [12].In these experiments, as in the predator−prey theory model [3], only the temporal dynamics of the turbulence−flow interaction is studied. Even though the spatial structure of the oscillating flow in the plasma edge region is shown in TJ−II [10] and AUG [11] and in a wider radial region in H−1 [13,14], no information is given on its spatial evolution or spatial propagation. However, as it has been pointed out in Ref. [15], where the 0−dimensional predator−prey theory model is upgraded toward a 1−dimensional one, the spatial evolution should also be taken into account as a necessary step to go towards the L−H transition model.The present work addresses for the first time this fundamental issue from the experime...

show abstract

Doppler reflectometer system in the stellarator TJ-II

Cited by 107 publications

References 22 publications

Core turbulence behavior moving from ion-temperature-gradient regime towards trapped-electron-mode regime in the ASDEX Upgrade tokamak and comparison with gyrokinetic simulation

Core turbulence behavior moving from ion-temperature-gradient regime towards trapped-electron-mode regime in the ASDEX Upgrade tokamak and comparison with gyrokinetic simulation

Scale-selective turbulence reduction in H-mode plasmas in the TJ-II stellarator

Spatiotemporal Structure of the Interaction between Turbulence and Flows at the L-H Transition in a Toroidal Plasma

Contact Info

Product

Resources

About