Characteristics and improved method of vacuum plug brazing for RFQ fabrication

At the Korea Multi-purpose Accelerator Complex (KOMAC), a radiofrequency quadrupole (RFQ)-based compact accelerator with 1 MeV/n output energy is under development, mainly for the test stand for developing accelerator technology and studying beam physics as well as for ion beam applications including semiconductor irradiation and neutron generation. The manufacturing procedure of an RFQ is complex, including two stages of brazing; one for plugging the cooling channel and the other is part assembling. The first brazing step plays the role of annealing process as well to relieve the stress generated during machining. Securing vacuum tightness after brazing is crucial, however, we experienced several failures in the plug brazing during the fabrication of the RFQ. Therefore, we investigated the characteristics of the plug brazing by conducting specimen tests and improved the brazing method based on the test results. This paper explains the successful and reliable approach for the plug brazing of a large structure.