The influence of the initial conditions on the pumping properties of the molecular sieves: P Lukác̆, Department of Experimental Physics, Komenský University, Bratislava, Czechoslovakia

Abstract

The incorporation of a titanium bulk sublimator in combination with a getter ion pump in a small accelerator vacuum system is shown to provide major advantages in pumping performance, reduction of the tritium hazard, and improvement in system reliability. A mode of operation is suggested for the sublimator which can greatly increase sublimator lifetime. Typical operating data for the vacuum system of a 300 kilovolt accelerator equipped with a sublimatorlion pump combination are presented. A proposal for the adaptation of a comparable vacuum system to a standard 150 kilovolt accelerator is made.A combination of a titanium bulk sublimator (TBS) and a getter-ion pump has been applied to the vacuum system of a 300 kilovolt accelerator used for the production of neutrons and offers the following advantages:(1) Routine pumpdown from atmosphere to 10−7 torr in 1 hour.(2) A variable pumping speed of from several litres/sec to over 17,000 litres/sec depending upon pumping requirements for H2, O2, N2, CO and H2O.(3) It is estimated that a 400 gram loading in a TBS should last for 3½ years in a 300 kilovolt machine and over 10 years in a 150 kilovolt vacuum system.(4) System is completely sealed and provides for controlled venting for tritium absorbed during rough pumping.(5) Tritium released from the target is permanently buried in the walls of the sublimator as titanium tritide thus reducing substantially the hazard associated with pump maintenance. Operation of the titanium sublimator in the region where the deuterium gas leak into the vacuum system matches the diffusion of deuterium into the titanium substrate can signifi- cantly extend the life of the TBS. Use of this design criteria should prove extremely valuable when applied to high current low voltage accelerators that use highly loaded tritium targets.