External excitation of a short-wavelength fluctuation in the Alcator C-Mod edge plasma and its relationship to the quasi-coherent mode

Golfinopoulos, T.; LaBombard, B.; Parker, R.; Burke, W.; Davis, E.M.; Granetz, R.; Greenwald, M.; Irby, J.; Leccacorvi, R.; Marmar, E.; Parkin, W.; Porkoláb, M.; Terry, J. L.; Vieira, R.; Wolfe, S.

doi:10.1063/1.4873595

Cited by 10 publications

(21 citation statements)

References 48 publications

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“…Indeed QC modes and low frequency fluctuations can overlap in case of low v E×B . Furthermore, TEM frequency spectrum becomes broadband in gyrokinetic simulations performed at larger R/L Te and R/L ne drives and there exist edge phenomena not attributed to TEM which can have a rather similar QC signature [39][40][41][42][43].…”

Section: Resultsmentioning

confidence: 99%

Identification of trapped electron modes in frequency fluctuation spectra

Arnichand

Citrin

Hacquin

et al. 2015

Plasma Phys. Control. Fusion

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Abstract.Ion temperature gradient (ITG) and trapped electron modes (TEM) are two important micro-instabilities in the plasma core region of fusion devices (r/a ≤ 0.9). They usually coexist in the same range of spatial scale (around 0.1 < k ⊥ ρ i < 1), which makes their discrimination difficult. To investigate them, one can perform gyrokinetic simulations, transport analysis and phase velocity estimations. In Tore Supra, the identification of trapped electron modes (TEM) is made possible due to measured frequency fluctuation spectra. Indeed, turbulent spectra generally expected to be broad-band can become narrow in case of TEM turbulence, inducing "quasi-coherent" (QC) modes named QC-TEM. Therefore the analysis of frequency fluctuation spectra becomes a possible tool to differentiate TEM from ITG. We have found indications that the TEM can have a QC signature by comparing frequency fluctuation spectra from reflectometry measurements, gyrokinetic simulations and synthetic diagnostic results. Then the scope of the analysis of QC-TEM are discussed and an application is shown, namely transitions between TEM turbulence and MHD fluctuations.

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Section: Resultsmentioning

confidence: 99%

Identification of trapped electron modes in frequency fluctuation spectra

Arnichand

Citrin

Hacquin

et al. 2015

Plasma Phys. Control. Fusion

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“…Recent progress in the understanding of the QCM include the identification of the QCM as a LCFS spanning electron drift-wave with interchange and electromagnetic contributions 10 and the excitation of QCM-like fluctuations using a dedicated LFS antenna 15 . The EDA H-mode plasmas studied here are obtained in reversed field, upper single-null configuration, with the ion gradB drift towards the active X-point.…”

Section: Experimental Setup and Diagnosticsmentioning

confidence: 99%

Radial localization of edge modes in Alcator C-Mod pedestals using optical diagnostics

Theiler

Terry

Edlund

et al. 2017

Plasma Phys. Control. Fusion

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Dedicated experiments in ion cyclotron range heated Enhanced D-alpha (EDA) H-mode and I-mode plasmas have been performed on Alcator C-Mod to identify the location of edge fluctuations inside the pedestal and to determine their plasma frame phase velocity. For this purpose, measurements from gas puff imaging (GPI) and gas puff charge exchange recombination spectroscopy (GP-CXRS) have been collected using the same optical views. The data suggest that the EDA H-mode-specific quasi-coherent mode (QCM) is centered near the radial electric field (E r ) well minimum and propagates along the ion diamagnetic drift direction in the plasma frame. The weakly coherent mode (WCM) and the geodesic acoustic mode (GAM) observed in I-mode, on the other hand, are found to be located around the outer shear layer of the E r well. This results in a weak plasma frame phase velocity mostly along the electron diamagnetic drift direction for the WCM. The findings in these EDA H-mode plasmas differ from probe measurements in ohmic EDA H-mode [B. LaBombard et al., Phys. Plasmas 21, 056108 (2014)], where the QCM was identified as an electron drift-wave located several mm outside the E r well minimum in a region of positive E r . To explore if instrumental effects of the optical diagnostics could be the cause of the difference, a synthetic diagnostic for GPI is introduced. This diagnostic reproduces amplitude ratios and relative radial shifts of the mode profiles determined from poloidally and toroidally oriented optics and, if instrumental effects related to GP-CXRS are also included, indicates that the measured location of the QCM and WCM relative to the E r well reported here is only weakly affected by instrumental effects.

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“…Another approach tries to more directly mimic the intrinsic plasma behavior by driving the QCM-or WCM-like fluctuations in the plasma with an external antenna. 195 This so-called "shoe-lace" is essentially an active MHD antenna for short wavelength electromagnetic modes. The antenna is named after the geometry of the antenna winding, which can drive currents in the plasma edge in the relevant k range (see Fig.…”

Section: External Control Of Edge Transportmentioning

confidence: 99%

20 years of research on the Alcator C-Mod tokamak

et al. 2014

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The object of this review is to summarize the achievements of research on the Alcator C-Mod tokamak [Hutchinson et al., Phys. Plasmas 1, 1511 and Marmar, Fusion Sci. Technol. 51, 261 (2007)] and to place that research in the context of the quest for practical fusion energy. C-Mod is a compact, high-field tokamak, whose unique design and operating parameters have produced a wealth of new and important results since it began operation in 1993, contributing data that extends tests of critical physical models into new parameter ranges and into new regimes. Using only highpower radio frequency (RF) waves for heating and current drive with innovative launching structures, C-Mod operates routinely at reactor level power densities and achieves plasma pressures higher than any other toroidal confinement device. C-Mod spearheaded the development of the vertical-target divertor and has always operated with high-Z metal plasma facing componentsapproaches subsequently adopted for ITER. C-Mod has made ground-breaking discoveries in divertor physics and plasma-material interactions at reactor-like power and particle fluxes and elucidated a) Paper AR1 1, Bull. Am. Phys. Soc. 58, 21 (2013). b) Invited speaker.

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External excitation of a short-wavelength fluctuation in the Alcator C-Mod edge plasma and its relationship to the quasi-coherent mode

Cited by 10 publications

References 48 publications

Identification of trapped electron modes in frequency fluctuation spectra

Identification of trapped electron modes in frequency fluctuation spectra

Radial localization of edge modes in Alcator C-Mod pedestals using optical diagnostics

20 years of research on the Alcator C-Mod tokamak

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