Analysis of Hydrocarbons in the Exhaust Gas of a Fusion Test Device Using Infrared Absorption Spectroscopy

To investigate the behavior of hydrogen isotopes in a large fusion test device, a new technique using infrared absorption spectroscopy is applied for the monitoring of hydrocarbons in exhaust gas. Fourier transform infrared (FT-IR) spectroscopy combined with a gas cell, which has an optical path length of 16 m, was installed at the plasma exhaust line. In this configuration, the detection limit of CH4, C2H6, C2H4, and CO is at the level of sub-ppm. The exhaust gas observations were conducted during hydrogen glow discharge and during the regeneration operation of cryosorption pumps during the hydrogen plasma phase. As a result, hydrocarbons and carbon monoxide were detected in the exhaust gas, and the exhaust behavior and the ratio of gas components were determined. It is also demonstrated that light and the heavy hydrocarbons can be discriminated by the FTIR system. Our infrared absorption spectroscopy study provides positive prospects for its application to exhaust gas analyses. (C) 2020 The Japan Society of Plasma Science and Nuclear Fusion Research