The ISR vacuum system

Early in September 1969, a pressure of 5 x10⁻¹¹ torr was achieved in a pilot section (16 m long) of the ISR vacuum system. This was the first section in the ISR tunnel which was baked. Five 'bake-outs' at different temperatures and of different duration had been carried out (150 - 300 °C, 4-20 hours). The main purpose, apart from testing the bake-out equipment, was to find the best bake-out procedure. Before each new bake-out the chamber was exposed to atmosphere. An average pressure of 10⁻⁹ torr had been specified for the ISR, but pressures of 10⁻¹⁰ torr or better could be achieved in uncomplicated sections like this pilot section. The average pressure in the completed rings was to be determined by those sections where something went wrong (such as poor pump performance, contamination or leaks). Up to 17 September, out of a length of near 2000 m of vacuum system, 180 m were installed and 60 m were under vacuum. The installation proceeded at a rate of about 40 m per week.