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Optical Hygrometers
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2018
UV spectral range is also of interest for optical hygrometers development. In this spectral range there are several emission lines, which are of particular significance in the humidity measurement due to their high selectivity to water. These are, for example, the Lyman–alpha line and the line of krypton (123.6 nm). Lyman–alpha radiation λ(Lα) is emitted by hydrogen atoms H(2P–2S) at a narrow line in the far UV portion of the spectrum at λ = 121.56 nm (Figure 3.28). It is produced by an electrical discharge in hydrogen. The wavelength of the Lyman–alpha line coincides with a deep absorption minimum in transmission spectra of air due to the presence of water vapor.
Design of Heat-Resistant in-Vessel Components for Deuterium Beam-Aided Charge Exchange Recombination Spectroscopy in JT-60SA
Published in Fusion Science and Technology, 2022
A. Terakado, Y. Koide, M. Yoshida, T. Nakano, H. Homma, N. Oyama
Figure 4 shows the diagnostic window at the tip of the port plug. The diagnostic window consists of one cover glass, one cover glass frame, one vacuum flange with sapphire glass window, and other frames. The cover glass is made of quartz. Most of the radiation power from the plasma is contributed by vacuum ultraviolet light. For example, the Lyman alpha line of C5+ (wavelength is 3.37 nm) attenuates to 1% at a thickness of 2 μm from the surface of the quartz glass.4 Therefore, the cover glass can work as a heat shield for the sapphire glass. The cover glass is supported by a polybenzimidazole (PBI) plastic frame. PBI has a similar linear expansion coefficient value to the quartz glass, which reduces thermal stress in the cover glass. The vacuum flange with sapphire glass window was selected based on a shock test of 60 G (Ref. 5) and operating in the JT-60U. The sapphire glass is brazed with Ag-Cu to a KOVAR sleeve made of Fe-Ni-Co alloy. The maximum temperature of the vacuum flange with sapphire glass window is limited to 300°C by the KOVAR sleeve.