The Physics And Experiment Research Of Extremely Low β Superconducting CH Cavity

Accelerator Driven Sub-critical System(ADS) is one of the most effective methods to approach the clean fission energy. At present, most of the labs in the world prefer to use superconducting(SC) cavity after the normal conducting low energy RFQ to accelerate ions. But in the very low beta section, there isn’t any mature design of cavity. Superconducting CH cavity, with the feature of high accelerating gradient and mechanical rigidity, is an ideal option to connect the low energy RFQ and the middle energy superconducting cavity. There are a series of key physical and technological problems need to be solved, such as CH cavity design, manufacture of high purity Nb cavity, welding, cleaning, testing, high power coupling, and so on. The development of superconducting CH cavity will provide a solution to superconducting cavity in the low beta section in ADS.There are two stages in the developing superconducting CH cavity.First the 162.5MHz, beta 0.065 copper model cavity was designed, fabricated and tested. This is a verification of the superconducting cavity design and fabrication process. The electromagnetic field, tuning, coupling and field flatness of CH cavity were researched during the copper model cavity, and corresponding solutions were given.Then the optimization design of superconducting CH cavity, construction and surface treatment was completed. At a low temperature of 4K the CH cavity was tested. The accelerating gradient and quality factor of the CH cavity was far exceeding the requirements of technical specifications of ADS accelerator.During the CH cavity design, the structure was optimized to reduce the maximum surface magnetic field, which greatly improves the performance and potential of the cavity. The mechanical and high-frequency coupling analysis was performed to determine the final reinforcement. The niobium CH cavity was completed by stamping, machining and vacuum electron beam welding and other processing. To improve the performance of superconducting cavities CH, we successful do the ultrasonic cleaning, heavy chemical polishing BCP, 800 degree vacuum annealing furnace exclude the hydrogen, the light chemical polishing, ultra-high pressure water raising HPR, 120-degree low-temperature baking and installation of magnetic shielding barrels. The maximum peak electric field was reached 61 MV / m for the cavity, and quality factor Q0 was better than 1.5 × 109. Corresponding to the acceleration gradient was 11 MV / m, an acceleration voltage of 4.1MV.