TiN coating of the PEP-II low-energy aluminum arc vacuum chambers

Abstract

The PEP-II Low-Energy Ring will operate at a nominal energy of 3.1 GeV with a positron beam current of 2.1 A. Design parameters for vacuum components are 3.5 GeV at 3 A. The arc vacuum system is based on an aluminum antechamber concept. It consists of 192 pairs of 2 m long magnet chambers and 5.5 m long pumping chambers. Titanium nitride coating of the entire positron duct is needed in order to suppress beam instabilities caused by multipactoring and the "electron-cloud" effect. An extensive R&D program has been conducted to develop coating parameters that give proper stoichiometry and a suitable thickness of TiN. The total secondary emission yield of TiN-coated aluminum coupons has been measured after the samples were exposed to air and again after electron-beam bombardment. A coating facility has been built to cope with the large quantity of production chambers and the very tight schedule requirements.