Relations between light emission and electron density and temperature fluctuations in a helium plasma

Abstract

The relations between three atomic lines, He I 667.8 nm (3 1 D ! 2 1 P), 706.5 nm (3 3 S ! 2 3 P), and 728.1 nm (3 1 S ! 2 1 P), and the underlying fluctuations in a helium plasma are investigated for the quantitative interpretation of optical observations in plasma fluctuation measurements. Frequency dependent fluctuation amplitude ratios and phase delays between the line emission fluctuation and the electron density and temperature fluctuations are calculated based on a quasi-static collisionalradiative model and a linear approximation technique. For frequencies up to the upper limit of practical interest (<1 MHz), the fluctuation amplitude ratios and phase delays are similar to those directly evaluated by the quasi-static model. It is found that the difference between the results from the linear approximation technique and from the quasi-static model is due to the absence of metastable fluctuations. Contributions of the 2 1 S and 2 3 S metastable fluctuations to the three helium line emission fluctuations are analyzed. The linearity between fluctuations in the line emission and in the electron density and temperature is valid for fluctuation levels higher than 10%.

Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

“…Ma et al looked at the response of the helium system over a wide range of frequencies and found that the simple CR model is adequate at MHz and slower frequencies. 136 More complex behavior was found at higher frequencies.…”

Measurements of electron density and temperature in the H-1 heliac plasma by helium line intensity ratios

“…The energy levels, excepting the ground state, are assumed to satisfy the quasi-static approximation. 26 The recombining plasma component is neglected, since the ionizing plasma component is the dominant part for n e < 10 14 cm −3 and T e > 5 eV. 13 The ionizing plasma condition does not require the neutral density to be measured and this simplifies the diagnostic.…”

“…It is planned to use the inferred plasma n e and T e information for characterizing the plasma temperature and density fluctuations. 26 In Sec. II, the tomography approach for reconstructing spectral line radiances and radiance ratios from line-of-sight measurements and the helium line intensity ratio technique based on a CR model are described.…”

A leader‐return‐stroke consistent macroscopic model for calculations of return stroke current and its optical and electromagnetic emissions

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