Determination of the electron density in the tokamak edge plasma from the time evolution of a laser-induced fluorescence signal from atomic helium

Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.

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Improvements to a laser-induced fluorescence instrument for measuring SO<sub>2</sub> – impact on accuracy and precision

Atmospheric Measurement Techniques ◽

10.5194/amt-14-2429-2021 ◽

2021 ◽

Vol 14 (3) ◽

pp. 2429-2439

Author(s):

Pamela S. Rickly ◽

Lu Xu ◽

John D. Crounse ◽

Paul O. Wennberg ◽

Andrew W. Rollins

Keyword(s):

Limit Of Detection ◽

Laser System ◽

Fluorescence Emission ◽

Laser Induced Fluorescence ◽

Fluorescence Signal ◽

Fluorescence Emission Spectrum ◽

Signal Ratio ◽

Accuracy And Precision ◽

Aromatic Species

Abstract. This work describes key improvements made to the in situ laser-induced fluorescence instrument for measuring sulfur dioxide (SO2) that was originally described by Rollins et al. (2016). Here, we report measurements of the SO2 fluorescence emission spectrum. These measurements allow for the determination of the most appropriate bandpass filters to optimize the fluorescence signal, while reducing the instrumental background. Because many aromatic species fluoresce in the same spectral region as SO2, fluorescence spectra were also measured for naphthalene and anisole to determine if ambient SO2 measurements could be biased in the presence of such species. Improvement in the laser system resulted in better tunability, and a significant reduction in the 216.9 nm laser linewidth. This increases the online/offline signal ratio which, in turn, improves the precision and specificity of the measurement. The effects of these improvements on the instrumental sensitivity were determined by analyzing the signal and background of the instrument, using varying optical bandpass filter ranges and cell pressures and calculating the resulting limit of detection. As a result, we report an improvement to the instrumental sensitivity by as much as 50 %.

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Low-temperature and low-pressure effective fluorescence lifetimes and spectra of gaseous anisole and toluene

Applied Physics B ◽

10.1007/s00340-021-07605-w ◽

2021 ◽

Vol 127 (4) ◽

Author(s):

M. Beuting ◽

T. Dreier ◽

C. Schulz ◽

T. Endres

Keyword(s):

Fluorescence Spectra ◽

Laser Induced Fluorescence ◽

Analytical Determination ◽

Fluorescence Signal ◽

Fluorescence Lifetimes ◽

Pressure Sensing ◽

Applicable Range ◽

Ladder Models ◽

First Time

AbstractFluorescence spectra and lifetimes of anisole and toluene vapor in nitrogen have been measured at conditions below ambient (257–293 K and 100–2000 mbar) upon excitation with 266-nm laser light to expand the applicable range of anisole and toluene laser-induced fluorescence (LIF) for conditions below room temperature that occur in expanding flows and cases with strong evaporative cooling. Anisole fluorescence spectra broaden with decreasing pressure while fluorescence lifetimes decrease simultaneously. This is consistent with a more pronounced effect of internal vibrational redistribution on the overall fluorescence signal and can be explained by significantly reduced collision rates. In the case of toluene, the transition from photo-induced heating to photo-induced cooling was observed for the first time for 266 nm. The data confirm predictions of earlier work and is particularly important for the advancement of the available photo-physical (step-ladder) models: since those transitions mark points where the molecules are already thermalized after excitation (i.e., no vibrational relaxation occurs during deactivation), they are important support points for fitting empirical parameters and allow analytical determination of the ground state energy transferred to the excited state. The data enable temperature and/or pressure sensing, e.g., in accelerating cold flows using laser-induced fluorescence of both tracers.

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Comment on determination of electron temperature from Langmuir probe data in tokamak edge plasma

Czechoslovak Journal of Physics ◽

10.1007/bf01597863 ◽

1990 ◽

Vol 40 (6) ◽

pp. 678-685 ◽

Cited By ~ 1

Author(s):

J. Dvořáček ◽

M. Tichý ◽

L. Kryška ◽

J. Stöckel ◽

F. Žáček ◽

...

Keyword(s):

Electron Temperature ◽

Langmuir Probe ◽

Edge Plasma ◽

Tokamak Edge

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Improvements to a laser-induced fluorescence instrument for measuring SO<sub>2</sub>: impact on accuracy and precision

10.5194/amt-2020-435 ◽

2020 ◽

Author(s):

Pamela S. Rickly ◽

Lu Xu ◽

John D. Crounse ◽

Paul O. Wennberg ◽

Andrew W. Rollins

Keyword(s):

Limit Of Detection ◽

Fluorescence Emission ◽

Laser Induced Fluorescence ◽

Fluorescence Signal ◽

Fluorescence Emission Spectrum ◽

Signal Ratio ◽

Accuracy And Precision ◽

Aromatic Species

Abstract. This work describes improvements made to the in-situ laser induced fluorescence SO2 instrument as originally described in Rollins et al. (2016). We report measurements of the SO2 fluorescence emission spectrum. These measurements allow for the determination of the most appropriate bandpass filters to optimize the fluorescence signal while reducing the instrumental background. Because many aromatic species fluoresce in the same spectral region as SO2, fluorescence spectra were also measured for naphthalene and anisole to determine if ambient SO2 measurements may be biased in the presence of such species. In addition, the 216.9 nm laser linewidth was decreased in order to increase the online/offline signal ratio which in-turn increases the precision of the measurement. The effects of these improvements on the instrumental sensitivity were determined by analyzing the signal and background of the instrument using varying optical bandpass filter ranges and cell pressures and calculating the resulting limit of detection. As a result, we report an improvement to the instrumental sensitivity by as much as 50 %.

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