Studies on superconducting thin films for SRF applications

In order to overcome the fundamental limit of Nb's critical magnetic field ({approx} 200 mT) that corresponds to E{sub acc} {approx}50 MV/m, an idea of coating several thin layers of a superconductor has been proposed. MgB{sub 2}, a superconductor that has a T{sub c} of {approx}39 K, has been studied to explore the effect of coating in terms of DC and RF critical magnetic fields, and RF surface losses. MgB{sub 2} has shown an excellent behavior, although there is some discrepancy between DC and RF measurements.