Development and study of superconducting SHF resonators for electron accelerators

The objective of the work is to reveal the most important conditions determining the fabrication of superconducting SHF resonators with high limiting parameters. Investigations are carried out with resonators with a knock-down design fabricated of niobium with a resistance ratio of 170, 200 and 400 operating on Hsub(001) wave at a frequency of 9.5 GHz. It is established that mechanical treatment plays a dominant role and may simlify essentially the requirements to the electrochemical polishing process. To produce the resonator operating surface with a roughness of 0.3-0.7 μm with the minimum damage of a current carrier layer, removal of the latter up to the operating surface of a metal layer 1 mm thick is accomplished by steps not more than 0.03 mm. Resonators with a Q-factor about109-1010 are to have shifts of face covers not higherthan 10 μm per 5 cm. To provide high operating surface purity and reliability of cooling it is necessary to use a suspension units with lower location of fixing elements and direct resonator contact with liquid helium. A conclusion is drawn that for investigated resonators values of Q-factor about an order of 109-1010 and values of HF field amplitude about 0.1 T (20-25 MV/m) may be attained without the process ofhigh-vacuum high-temperature annealing. The systems with throttle joint may be used as accelerating structures of electron linear accelerators