Abstract
Helium (He) line emissions have been utilized to measure the electron density (ne) and temperature (Te), and validity checks have been conducted in various linear devices. In this study, we performed optical emission spectroscopy (OES) of He line emissions in the linear plasma device Magnum-PSI, where the used density range was 1–8 × 1020 m−3, which was much higher than those used until now. We observed nine line emissions in the wavelength range of 388–728 nm and deduced ne and Te based on comparisons with a collisional radiative model. From the variation of the difference between the experiments and calculations, the joint probability distribution of ne and Te was deduced. We will discuss the effect of radiation trapping, in particular, based on comparisons between OES measurement results and Thomson scattering measurements.
Highlights
Helium (He) line emissions from fusion edge/divertor plasmas provide important information for plasma diagnostics
After describing the experimental setup, we show two typical cases to make a detailed comparison with the collisional radiative (CR) model
It is difficult to see what the best choice for P is, the results show that noept and Teopt can be altered by the neutral density, and it can be an important factor to assess the joint probability distribution
Summary
Helium (He) line emissions from fusion edge/divertor plasmas provide important information for plasma diagnostics. It has been revealed that radiation trapping is an important effect to understand the population distribution of He atoms. The density range used in the linear devices was mainly less than 1019 m−3, which was lower than the actual fusion conditions. We performed optical emission spectroscopy (OES) of He lines in the Magnum-PSI device, where the plasma density can be higher than 1020 m−3. It is shown how the difference in the population distribution between the CR model and OES results alters when changing ne and Te used for the CR model. The joint probability distribution will be deduced from the difference between the CR model and experiments. Using the joint probability distribution, ne and Te from the OES are compared with those measured by laser Thomson scattering (TS) measurements
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