Progress on Coating of Superconductor MgB$_{2}$ on Cu RF Cavities

With a higher critical field$H_{c}$and critical temperature$T_{c}$than Nb and numerous Nb compounds and alloys, MgB$_{2}$is a promising material for superconducting radio frequency (SRF) cavities working at 10$\sim$20 K. We present our ongoing efforts towards the development of MgB$_{2}$-coated SRF cavities. MgB$_{2}$films, up to 4$\mu m$in thickness, were deposited onto 1.3GHz Tesla-type mock-up Cu RF cavities using a hybrid physical-chemical vapor deposition (HPCVD) process. A pair of clamshell resistive heaters was employed for heating the cavity through conduction. MgB$_{2}$films grown on 1 cm × 1 cm copper substrates attached to various positions on the inner wall of the cavities exhibited critical temperature ($T_{c}$) of up to 37.6K, determined by AC susceptibility measurements. Uniform MgB$_{2}$film coatings were achieved by moving the Mg and B sources in tandem with computerized control of deposition parameters. The MgB$_{2}$films were also characterized at RF frequencies using a dielectric resonator, which showed the same$T_{c}$as obtained from the AC susceptibility measurements.