Niobium sputtered quarter wave resonators

At LNL a research program on niobium sputtered copper quarter wave resonators is reaching its final stage. With respect to traditional superconducting QWRs (lead electroplated, bulk niobium and explosively bonded Nb/Cu cavities), higher performances and lower costs are expected for niobium sputtered copper QWRs. By obtaining high quality superconducting niobium films with good thickness uniformity inside the resonator it is demonstrated that, contrary to common belief, the tricky shape of QWRs is not an obstacle to the application of sputtering technology. The first prototypes realized up to now show, test after test, fast and progressive improvement. Each prototype provides more and more information about the variables that influence the final rf performance.