NSRRC Activity Report 2022

Facility Development and Status 099 NEXTorr Z 200 × 3), as illustrated in Fig. 2 , and implemented this design to construct a vacuum system for an elliptically polarized undulator (EPU). The proposed vacuum design possesses the following features and advantages compared with a previous design: 1. The design includes an extractor ionization gauge located at the center of the EPU chamber; it can accurately measure the pressure inside the chamber. 2. It includes a NEXTorr pump—a small, lumped NEG-ion combination pump—that pumps gases that cannot be absorbed by the NEG alone, including noble gases and methane. 3. It includes a ZAO NEG alloy (Zr–V–Ti–Al) that affords a faster pumping speed, a larger absorption capacity for all active gases, and less outgassing during NEG activation compared with a previously used St707 getter (Zr–V–Fe). 4. It includes two flat wires that are composed of flexible printed circuit boards laminated with Kapton foils on both sides (thickness 1.2 mm) and glued onto the upper and lower surfaces of the EPU chamber; the wires can correct the dynamic multipoles induced by the EPU. To evaluate the performance of the proposed vacuum design, this study constructed and tested two NEG cartridge-type vacuum systems. The tests included measuring the base pressure upon activation of the NEG pumps without baking, conducting a pressure-rise test by turning off the ion pumps (IPs), and measuring the dynamic pressure as a function of accumulated beam dose. The major difference between NEG cartridge-type and NEG strip-type vacuum systems is that NEG cartridge- type vacuum systems comprise three small diode IPs and each ion pump has pumping speeds of 6 and 15 L s −1 for argon and methane, respectively. This study evaluated the effect of the IPs on the vacuum pressure of the EPU chamber by turning off all of the NEXTorr IPs for 18 h and recording the corresponding increase in vacuum pressure, as displayed in Fig. 3 . The vacuum pressure after IP shutdown ( i.e. , pumping with only NEG) increased by approximately 55 times from 3.30 × 10 −11 to 1.83 × 10 −9 mbar (A in Fig. 3 ). Monitoring results obtained using a residual-gas analyzer (B in Fig. 3 ) indicated that the rise in pressure was attributed to the major gaseous species H 2 + (m/z = 2), He + (m/z = 4), CH 4 + (m/z = 16), Ar 2+ (m/z = 20), CO + (m/z = 28), Ar + (m/z = 40), and CO 2 + (m/z = 44), as presented in Fig. 4 . These data indicate that despite their Fig. 4 : Gas compositions inside the NEG cartridge-type vacuum systems, as measured using a residual-gas analyzer after 18 h of shutdown of the ion pumps. [Reproduced from Ref. 2] Fig. 3 : Pressure-rise curve of the NEG cartridge-type vacuum systems. [Reproduced from Ref. 2] modest pumping speed, the small IPs acted as auxiliary pumps to effectively regulate the vacuum pressure of the EPU chamber. The chamber pressure rapidly returned to its original level after the IPs were restarted (C in Fig. 3 ) During a long shutdown in September 2020, the two NEG cartridge-type vacuum systems were installed in the Taiwan Photon Source (TPS) storage ring for two insertion devices, namely EPU66 and EPU168. The vacuum chambers were pumped down to a pressure of < 1 × 10 −6 mbar in 5 h, and the NEG pumps were subsequently activated. After NEG activation, the chamber pressures quickly declined to approximately < 1 × 10 −8 mbar within hours, as illustrated in Fig. 5 (see next page). Notably, many gaseous molecules