Plasma and Fusion Research
Volume 18, 1402062 (2023)
Regular Articles
- 1)
- Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
- 2)
- National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
- 3)
- The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu 509-5292, Japan
- 4)
- College of Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan
Abstract
A digital phase analysis technique was applied to a 119-µm wavelength far-infrared (FIR) laser interferometer on the Large Helical Device (LHD). High-density plasma measurement without phase jumping was achieved, representing an improvement over measurements made using a conventional analog phase counter. Digital phase analysis became operational at a quarter of the threshold of the analog phase counter. The phase sensitivity was also improved using digital analysis because the noise level was reduced to approximately half that of the conventional analog phase counter. The improved phase sensitivity enabled measurement of small-amplitude fluctuations.
Keywords
plasma, interferometer, far-infrared laser, digital demodulation
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