Cryopumping the Omnitron Ultra-Vacuum System Using "Heat Pipes" and Metallic Conductors

The Omnitron (Fig. 1) is a synchrotron (120 ft. diam) accelerator with a concentric storage ring (130 ft. diam) that will deliver beams of light and/or heavy ions at different energies and currents. Storage of heavy ions in a high-charge state for 25 msec requires that the vacuum be specified more carefully than is common in everyday speech. (Reference to "air" and "pressure" serve well enough, if not taken too literally.) Thus in place of a pressure specificatio a conservatively crude figure of merit, 1014 ?? ??niZ21 is used where: N = 3??107 turns around the acceluator, ni = the concentration of atoms of the ith atomic number Zi. Cryopumping is done by cold fingers inserted in each gap between magnets on both the synchrotron and storage rings (190 pumping stations total - see Fig. 1). Each finger, consisting of an 80??K jacket around a 4??K core, is cooled at one end by metallic attachment to nitrogen and helium distribution rings. Pump-down tests of one full size pumping station (Figs 2 & 3) comprising an alumina beam tube brazed to stainless steel are reported using "heat pipes" (thermal siphons) and metallic heat conductors in the cold finger design. Superior pumping performance is achieved, i.e., pump down requires 7 hrs to the Omnitron figure of merit. A garden variety oil sealed mechanicel pump and an oil (convoil 20) diffusion pump provided with fail safe LN trap-valves are used.