Background: A Radio Frequency Quadruple (RFQ) accelerator was developed for China Spallation Neutron Source (CSNS). Purpose: The aim is to design a 3-MeV

20-mA H? RFQ accelerator. Methods: Lots of careful investigations

analysis

experimental tests were performed to solve the problem that came out in design and machining process. Results: The machining tolerance of RFQ measured by three-Coordinate Measuring Machine (CMM) was less than 20 μm; the unloaded Q value was 7 679

about 80% of the theoretical Q value; the flatness of RF electric field distribution was higher than 2.5% after several time tuning. After several days conditioning

the power feeding into the cavity reached 450 kW and maintained for 12 h without sparking. Negative hydrogen ion beam with energy of 3 MeV and current of 28 mA at the exit of RFQ was gotten in the beam commissioning afterwards. Conclusion: The current commissioning results of RFQ meets the requirement of CSNS

and the beam current can be improved in future. Abstract