Operational status of the vacuum system of the 300 m gravitational wave laser interferometer, TAMA300

TAMA300, a laser interferometric detector for gravitational waves, involves two vacuum ducts (300 m long, 400 mm in diameter) and eight vacuum chambers (2 m high, 1.2 m in diameter). All surfaces of the ducts and chambers were finished by electrochemical buffing so as to reduce the outgassing rate. The vacuum system was completed at the beginning of 1998. After 2000 h of pumping, the vacuum pressures in the ducts were 2.5 × 10^-6 Pa without baking, eventually reaching to 3 × 10^-7 Pa after 13000 h of pumping when the ducts were separated from the chamber. By February of 1999, the mirror suspension system was fully installed in the chambers. During the summer of 1999, a test-run of the entire system of TAMA300 was successfully made. The pressures in the ducts and chambers, during interferometer operation, are in the range of 2-3 × 10^-6 Pa, while the pressures in the chambers are kept at 1 × 10^-5 Pa.