Page 3 - Improved density profile measurements in the C-2U advanced beam-driven Field-Reversed Configuration (FRC) plasmas

11E514-3
D. Osin and T. Schindler
Rev. Sci. Instrum. 87, 11E514 (2016)
FIG. 5. Comparison of plasma parameters measured at t = 1 ms: (a) Te: Circles—Thomson scattering averaged over thirty shots, lines—DWIC sys- tem from three di↵erent shots; (b) ne in shot 49 761: Circles—Inverted CO2, squares—DWIC.
2.5 ms during the shot to have a time history of the measured plasma parameters. Good quality images were successfully acquired during the experiment with exposures as short as 10 μs. In this paper typical Te and ne images obtained at t = 1 ms with exposures of 25 μs are presented merely for demonstration of the diagnostics capability.
In order to determine either Te or ne, the experimentally obtained line ratios are compared with those calculated using atomic collisional-radiative codes, and available in the litera- ture, e.g., Ref. 8. Shown in Fig. 4 are typical Te and ne images observed by the DWIC in SOL plasma at t = 1.0 ms.
Comparison of T measured by the Thomson scattering e
laser diagnostics and the DWIC system, presented in Fig. 5, shows rather good agreement between the two independent diagnostic systems. Values of ne, observed by the DWIC in SOL plasma, agree with those obtained from the inverted line-integrated CO2 measurements within error bars of both diagnostics. The ne data produced by the DWIC have relatively large fluctuations, not seen in the Te images. The nature of these density fluctuations is not clear yet and will be addressed in the future.
V. SUMMARY
A dual wavelength imaging camera was built and installed on C-2U to observe 2D images of Te and ne in the SOL plasma (outside of FRC separatrix). Data obtained with the DWIC agree rather well with the main C-2U diagnostics. The DWIC system provides valuable measurements of plasma parameters, resolved in both space, 0.2 cm, and time, 10 μs, and can be used in the region inaccessible by the main C-2U diagnostics. The future upgrade includes reduction of the focus wavelength dependence, improvement of the light collection e ciency, and implementation of a fast rep- rate camera. A planned upgrade to a large format 1024 ⇥ 1024 pixels, high speed camera with 4 kHz rep-rate, and pixel size of 20 μm will enable us to take snapshots every 250 μs, with a spatial resolution of about 0.5 cm over 15 cm plasma region.
ACKNOWLEDGMENTS
We thank our shareholders for their support and trust, and all fellow TAE sta↵ for their dedication, excellent work, and extra e↵orts.
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