Study of the ultra-high-vacuum system of the 14-m-long vacuum chamber of the Taiwan Photon Source using the pressure build-up method

The pressure build-up method was suitable for diagnosing and qualifying the vacuum status in the chamber and thus can be applied to determine the maintenance and recovery of a large vacuum system. The thermal outgassing rate and the pumping speed can be estimated using this method. In its electron storage ring, the Taiwan Photon Source (TPS) contains 24 aluminum arc-cells that are 14 m in length. Each cell was baked ex situ to 150 °C for 24 h in the laboratory to achieve ultra-high-vacuum. The cells reached 6.4 × 10−9 Pa on average, under pumping with primarily ion pumps and non-evaporable getter (NEG) pumps. The thermal outgassing rate, the pumping speed, and the residual gas compositions of a typical cell were analyzed. With all ion pumps turned off for more than 80 h, the vacuum pressure rose to approximately 8 × 10−7 Pa. The measured pumping speed was 6.9 × 10−4 m3∙s−1 on average for most of the cells extractor gauges associated with major inert gases in the 14 m-long cells. An experimental analysis of the emitted residual gases indicated that the gas in the aluminum vacuum chamber was primarily CH4 after the ion pumps were deactivated. Moreover, the one-cell vacuum chamber recovered to UHV status on using the pressure build-up method, including calculation of the outgassing rate and the pumping speed.