Parametrization of reflectometry fluctuation frequency spectra for systematic study of fusion plasma turbulence

Sun, Yan; Sabot, R.; Hornung, Grégoire; Heuraux, S.; Hacquin, S.; Verdoolaege, Geert

doi:10.1063/1.5024366

Cited by 4 publications

(8 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The positions of the probing zone were recovered using the density profiles provided by the interferometry lines inversion. The frequency spectra exhibit a classical shape with low frequency and broadband components [27,28]. Unlike the Ohmic phase, the LHCD phase contained an increase of 15-20 dB of the background ECE noise.…”

Section: Density Fluctuation Measurements and Tem Turbulencementioning

confidence: 97%

Core tungsten transport in WEST long pulse L-mode plasmas

et al. 2020

Self Cite

View full text Add to dashboard Cite

Tungsten transport is investigated in WEST long pulse L-mode plasmas operated with the strike point on the actively cooled upper tungsten divertor. The pulses are mostly heated by lower hybrid waves. It is experimentally found that tungsten does not centrally accumulate throughout these ∼ 30 s reproducible discharges despite large normalised electron density gradients R/Ln e. To explain these observations, turbulent and neoclassical transport of electrons and tungsten ions are computed with GKW [1] and NEO [2, 3] respectively. Additionally, interpretative integrated modelling simulations are also performed to keep data coherency despite the lack of measurements of some quantities such as the Ti profiles. Modelled R/Ln e are found consistent with interferometry inversions and the tungsten peaking factor R/Ln W remains comparable to R/Ln e due to dominant turbulent diffusivities inside r/a = 0.3−0.8. In the central region r/a < 0.3 neoclassical W transport dominates but the convective velocities are several order of magnitudes lower compared to plasmas with toroidal rotation velocities induced by a neutral beam injection (NBI) torque. Finally, nitrogen is seeded in these pulses leading to an enhanced energy content which is consistent with stabilised ion temperature gradient modes from dilution.

show abstract

Section: Density Fluctuation Measurements and Tem Turbulencementioning

confidence: 97%

Core tungsten transport in WEST long pulse L-mode plasmas

et al. 2020

Self Cite

View full text Add to dashboard Cite

show abstract

“…Using a new parametrization method 21 , we have built a large database with more than 300, 000 reflectometry frequency spectra. A number of dependencies of the spectra have been studied in Ohmic and L-mode plasmas.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…The details of the data analysis techniques used to parametrize the fluctuation frequency spectra from core reflectometry 22 can be found in Ref. 21. We briefly recall the main aspects here.…”

Section: A Decomposition and Fit Of Frequency Spectrummentioning

confidence: 99%

“…In a first analysis of the database, radial profiles were investigated of the broadband contribution (E BB ) to the frequency spectra at different edge safety factor q ψ in Ohmic discharges. 21 Figure 3 shows one example of the radial profiles of E BB resulting from ∼ 30,000 measure- ments (cyan points) in ∼ 1,400 Tore Supra discharges under Ohmic conditions and with 4 < q ψ < 5. A drop of E BB , which we refer to as the E BB basin, was observed in the core region.…”

Section: B Database and Applicationmentioning

confidence: 99%

“…Based on earlier work regarding frequency spectrum decomposition by Vershkov et al 17,18 and Krämer-Flecken et al 19,20 , a parametrization method has been developed that reduces the number of parameters to describe the reflectometry power spectrum by two orders of magnitude 21 . This parametrization has allowed studies of dependencies of the reflectometry frequency spectra in Ohmic plasmas, distinguishing between the linear Ohmic confinement (LOC) and the saturated Ohmic confinement (SOC) regime.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Experimental trends of reflectometry frequency spectra emerging from a systematic analysis of the Tore Supra database

et al. 2019

Self Cite

View full text Add to dashboard Cite

One major goal of data science applications is to extract patterns from large data sets. Such a database approach has been applied, for the first time in fusion science, towards a systematic study of the frequency spectra computed from reflectometry signals in the Tore Supra database, which are related to density fluctuations. In particular, decomposition of reflectometry frequency spectra has allowed to discover and quantify general trends of spectral characteristics (fractional contribution, width) for different components in Ohmic and low-confinement mode (L-mode) plasmas. In Ohmic plasmas, the contribution of the broadband component (E BB ) to the total spectrum power in the saturated Ohmic confinement (SOC) regime is observed to be systematically higher than in the linear Ohmic confinement (LOC) regime. A transition of the dominating instability from TEM to ITG, could explain the observed spectral modifications, which are supported by analysis of the dependence of density peaking on collisionality. The spectral characteristics of the broadband (BB) and low-frequency (LF) components were then investigated in L-mode plasmas with ICRH or LH heating. The similar trends of the BB components with collisionality observed in L-mode plasmas compared with the Ohmic cases suggests a similar explain by linking the frequency spectra to the underlying instabilities. The database analysis motivates more detailed studies by full-wave and gyrokinetic simulations, in order to confirm this link for both Ohmic and L-mode plasmas.

show abstract

Extraction of quasi-coherent modes based on reflectometry data

Salazar¹,

Heuraux²,

Sabot³

et al. 2022

Plasma Phys. Control. Fusion

Self Cite

View full text Add to dashboard Cite

The identification of turbulence sources would drive to a deeper understanding of confinement dynamics in tokamak plasmas. Turbulence results from a mixture of instabilities corresponding to sources at different time and spatial scales. Using correlation reflectometry and multipin Langmuir probe (MLP), it was shown in the T-10 and TEXTOR tokamaks that the reflectometry frequency spectrum was the superposition of several components: broadband component, Quasi-Coherent (QC) modes and low frequency components. The relevance of QC modes is associated to their link with the Trapped Electron Mode (TEM) instability. A method is presented to extract the QC modes component from the reflectometry data enabling the separation from the broadband component and the study of its time evolution. It is a first step toward the discrimination of turbulence sources. The central idea explores a way to combine the approach of signal processing and machine learning: the Continuous Wavelet Transform (CWT) on the basis of complex Morlet wavelet has proven to be efficient in providing a decomposition of a signal at different scales over time for fluctuations tackling; clustering techniques as the Minibatch K-means are able to tackle clusters at different scales. The method was applied to Tore Supra and TEXTOR reflectometry data. On Tore Supra, the amplitude of the extracted QC mode component decreases during transition from the Linear Ohmic Confinement (LOC) to the Saturated Ohmic Confinement (SOC) regimes. On TEXTOR the amplitude of the coherent spectra of the extracted QC mode component is similar to the experimental coherent spectra obtained through correlation reflectometry. The developed method permits to extract components preserving their physical and statistical properties.

show abstract

Parametrization of reflectometry fluctuation frequency spectra for systematic study of fusion plasma turbulence

Cited by 4 publications

References 29 publications

Core tungsten transport in WEST long pulse L-mode plasmas

Core tungsten transport in WEST long pulse L-mode plasmas

Experimental trends of reflectometry frequency spectra emerging from a systematic analysis of the Tore Supra database

Extraction of quasi-coherent modes based on reflectometry data

Contact Info

Product

Resources

About