A new distributed ion pump made of aluminum alloy with an aluminum or a titanium cathode in the transposable ring intersecting storage accelerators in Nippon e+e− colliding ring

Abstract

The characteristics of the distributed ion pump (DIP) for TRISTAN (TMR) which has Al cathodes (Al-DIP) are described. The test of the Al-DIP showed a comparable initial pumping curve and pumping speeds (1/2–1/3) to the DIP which has a Ti cathode (Ti-DIP). But the Al-DIP in TMR showed a deteriorated pumping action. The reasons for this action were: (i) The surface of Al cathode was covered with a thicker oxide layer than those of the original cathode and of the tested DIP. (ii) The oxide layer was possibly grown in polyethelene envelopes with no desiccant, while the Al-DIP’s were transported and stocked before DIP assembly. (iii) The residual gases during a test evacuation of the deteriorated DIP in a TMR B chamber were H2 and H2O. (iv) A burst of H2 was observed after the DIP was turned on. An exponential increase of H2 was observed during the operation of DIP alone (before baking). (v) H2 decreased by about two orders after baking. These facts suggest that the H2 decomposed from the water contained in the thicker oxide on the cathode surface brought about the deteriorated action which was aided by the smaller pumping capacity rather than that of the Al-DIP test system.