Identification of trapped electron modes in frequency fluctuation spectra

Arnichand, H.; Citrin, J.; Hacquin, S.; Sabot, R.; Krämer‐Flecken, A.; Garbet, X.; Bourdelle, C.; Bottereau, C.; Clairet, F.; Giacalone, Jean-Claude; Guimarães-Filho, Z. O.; Guirlet, R.; Hornung, Grégoire; Lebschy, A.; Lotte, P.; Maget, P.; Medvedeva, A.; Molina, Diego Alonso Restrepo; Nikolaeva, V.; Prisiazhniuk, D.

doi:10.1088/0741-3335/58/1/014037

Cited by 36 publications

(55 citation statements)

References 50 publications

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“…First of all, it was found from the 1D full-wave computations that both O-mode and X-mode yield the same fluctuation spectra, even though the amplitude of phase fluctuations is larger for the X-mode. As presented in a previous paper 10 and depicted in Figure 9, the synthetic reflectometry results are in a good agreement with the experimental observations. Outstandingly, a QC-TEM mode is recovered in the LOC regime only, at a frequency ($100 kHz) consistent with the experiments.…”

Section: Discussionsupporting

confidence: 90%

“…5 While modifications of fluctuation spectra due to a change of turbulence regime have been reported from different diagnostics in various machines, [6][7][8][9] it was recently established that the ITG-and TEM-dominated regimes could be differentiated from the reflectometry spectra. 10 In the latter work, the experimental observations were supported by the non-linear gyrokinetic simulations, which qualitatively reproduced the shape of the reflectometry spectra in the ITG and TEM regimes. A direct and more quantitative comparison of the gyrokinetic computations with the experimental results requires the use of synthetic diagnostics, the development of which has become widespread in a fusion research.…”

Section: Introductionsupporting

confidence: 55%

“…It is also striking to note that, while a large broadband spectrum is observed in the SOC regime, a QC-TEM mode appears in the spectrum at around 120 kHz in the LOC regime, thereby confirming the experimental findings. 10 The complex form a(t).e ju(t) of the reflectometry signals instead of their phase is often used for spectral analysis, this having the effect to broaden the spectrum and add some harmonics resulting from a combination between the main frequency components. The spectra obtained from the FFT of the complex signals are also displayed (dashed lines) in Fig.…”

Section: B Comparison Between O-mode and X-mode Resultsmentioning

confidence: 99%

“…17 The fluctuation spectra inferred from the reflectometry measurements usually show some distinct features in the ITG-and TEM-dominated regimes. While a broadband spectrum is typically observed in the ITG-dominated regimes, the appearance of quasi-coherent modes in the TEM-dominated regimes has been evidenced in a number of the existing fusion devices: T-10, 18 TEXTOR, 19 Tore Supra, 10,13 JET, 20 ASDEX-Upgrade, 10 etc. The quasi-coherent modes associated with TEM-dominated turbulence (QC-TEM) can be identified in the frequency spectra of the reflectometry signals displaying a carrier frequency on the order of magnitude of 50-150 kHz with a bandwidth of about 10-50 kHz.…”

Section: A Experimental Observations From the Reflectometry Measuremmentioning

confidence: 99%

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Simulation of core turbulence measurement in Tore Supra ohmic regimes

Hacquin¹,

Citrin²,

Arnichand³

et al. 2016

Physics of Plasmas

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This paper reports on a simulation of reflectometry measurement in Tore Supra ohmic discharges, for which the experimental observations as well as gyrokinetic non-linear computations predict a modification of turbulence spectrum between the linear (LOC) and the saturated ohmic confinement (SOC) regimes. Synthetic reflectometry simulations coupling full-wave computations with gyrokinetic data are carried out. This allows a direct comparison between the gyrokinetic non-linear predictions and experimental observations. The synthetic diagnostic results are found in a good agreement with the experimental findings; in particular, they reproduce well the quasi-coherent peak in the fluctuation spectrum of LOC regimes dominated by a trapped electron mode turbulence. It is also shown that such synthetic tools are valuable for (i) an enhanced interpretation of the reflectometry measurement (for instance, through the investigation of the 2D effects) and (ii) a better understanding of the turbulence properties (for instance, via the analysis of its poloidal asymmetry).

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Section: Discussionsupporting

confidence: 90%

Section: Introductionsupporting

confidence: 55%

Section: B Comparison Between O-mode and X-mode Resultsmentioning

confidence: 99%

Section: A Experimental Observations From the Reflectometry Measuremmentioning

confidence: 99%

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Simulation of core turbulence measurement in Tore Supra ohmic regimes

Hacquin¹,

Citrin²,

Arnichand³

et al. 2016

Physics of Plasmas

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“…It is worth noting that there are cases where the LOC/SOC transition is correlated with the changes in dominant turbulence mode from TEM to ITG in gyrokinetic simulations. 30,50,60 This study also suggests that TEM is relatively more important in the LOC discharge compared to the SOC discharge. However, it is also true that both discharges have "mixed mode" and this study results are not fit into the old hypothesis.…”

Section: Discussionmentioning

confidence: 54%

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

et al. 2016

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Long wavelength turbulent electron temperature fluctuations (kyρs < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (kyρs ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].

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