Production process of alumina-ceramic vacuum chambers for J-PARC

Abstract

In order to avoid the eddy-current effect due to a rapid-cycling magnetic field in the J-PARC proton synchrotron ring (348 m in circumference), several tens of ceramic chambers (3.5-m long and 500 mm in diameter, at their maximum) are to be installed. The 99.7% alumina ceramic ducts of sub-meter in length, having racetrack and circular cross-sections were sintered and jointed by braze. Several chambers of rectangular and racket-shape cross sections were also produced. A TiN film of 15 nm thick was formed inside the chambers for suppressing secondary electron emission, and electroformed copper stripes were plated outside for lowering the beam-impedance. The course of the production process, including polishing, metallizing and brazing to a titanium flange is reported. Outgassing rates were also measured for a few of the chambers by a conductance-modulation method.