Upgrade design for vacuum system of TRISTAN accumulation ring

Abstract

Present operational parameters of TRISTAN accumulation ring (TAR) are 6.5 GeV, 30 mA with 6 hours been lifetime as a synchrotron radiation source and 8 GeV, 20 mA as an injector to the main ring. The accumulation ring has several modes of operation: as a synchrotron radiation source, an injector for the planned B(B‐meson)‐factory and an injector for the TRISTAN main ring. The required maximum beam current and lifetime depend on the application. In order to improve performance for use as a dedicated synchrotron light source, it is desirable to improve the beam current and lifetime. The design goal of the upgrade is 100 mA at 8 GeV. In order to achieve this goal, the effective pumping speed of the Distributed Ion Pump (DIP) was increased by a factor of 3. For the quadrupole magnet chambers, Non‐Evaporable Getter (NEG) cartridges are more suitable. The effective average pumping speed along the ring as a whole will be three times higher than that of the present TAR. On the other hand, the present beam current cannot be raised more than 30 mA at 6.5 GeV because absorbers of ceramic chambers for kicker magnets have poor cooling and radiation power shielding functions. The newly designed ceramic chambers are protected by new water cooled absorbers and offset structure. After installation, it is expected that the improved beam current and lifetime will be obtained quickly once the modification has been made. UHV performance of individual components must be confirmed by preassembling, prebaking, and preconditioning of the DIP, lumped Sputter‐Ion Pump (SIP), Titanium Sublimation pump (TSP), and NEG before installation. All assembly is done in a clean room. The chamber material has been changed from A6063 alloy to high purity 99.99% aluminum.