Operation Experience of Tetrode Vacuum Tubes in J-PARC Ring RF System

Abstract

Final stage amplifiers of the J-PARC Ring rf system have almost the same design for both the RCS and MR, and both use the same tetrode vacuum tubes. Operation of the RCS began in 2007, and of the MR in 2008. Total operation time of the RCS is more than 50,000 hours, and more than 40,000 hours for the MR. In 2018, two tubes at the MR reached their end of life; it was the first such case for the J-PARC Ring rf system, with the exception of a few initial failure. It is known that the long life of the tubes can be achieved by the reduced filament voltage compared with the rated value. In this instance, the filament voltage is 7-15 % lower than the rated value in the RCS, and 4-11 % lower in the MR. We observed the difference in voltage reduction exhibited as a difference in the reduction of filament resistance, which serves as an indication of tube lifetime. In this paper, we describe the measurement results of the filament parameters and tendency for reduction of the filament resistance in the RCS and MR.