Performance of the NBS-LANL RTM injection line vacuum system

A 1000 1/sec cryopump is used to provide the hydrocarbon-free vacuum required for the 100 keV electron beam transport line of the NBS-LANL Racetrack Microtron. The beam line is 3.5 cm in diameter and 4 m long. To overcome the low vacuum conductance of the beam line, it is pumped every 1/2 meter by a 15 cm diameter vacuum manifold which is connected to the cryopump. A single cryopump is used rather than several ion pumps to reduce costs and to provide easier starting. An oil-free roughing pump and sorption pump are used in the initial pumpdown. The vacuum system is all metal sealed. Vacuums of 3 x 10-6 Pa are reached in 8 hours from atmospheric pressure without baking out the system, and ultimate vacuums of 5 x 10-7 Pa are achieved