Operational Characteristics of the Tristan Accumulation Ring Vacuum System

The operational characteristics of the TRISTAN vacuum system is discribed. The vacuum system is made of aluminum alloys using specially extruded aluminum pipes. The best base pressure, on the order of 10 Pa, was obtained without any baking or discharge cleaning. The thermal gas desorption rate of the aluminum chambers was on the order of 10-10 Pa.1/s.cm2. For a time integrated beam current of 13.5 A.h, the pressure rise due to synchrotron radiation was 2.1 × 10-8 Pa/mA and the maximum beam lifetime was about 2 hours at several mA. The pressure rise is approximately inversely proportional to the time integrated beam current and is initially proportional to the beam energy, changing after about 7 A. h, to being proportional to the square root of the beam energy. A pressure independent lifetime of 357 min was observed. The lifetime at higher beam currents is proportional to the time integrated beam current. No thermal problems due to synchrotron radiation were observed. Corrosion due to high energy radiation in the presence of humidity was found in the aluminum windows for X-rays and y-rays. Heating problems due to wall current discontinuities did not occur in the dual flat mirror surface seal type gate valves made of aluminum alloys. They were observed in a current transformer, in the ceramic chambers, and in a normal, Viton sealed gate valve.