| Multilayer films on the interior of a superconducting radio frequency (SRF) accelerating cavity have the potential to increase the lower critical magnetic field Hc1 of the bulk cavity material [A. Gurevich, Appl. Phys. Lett. 88, 012511 (2006)]. A cavity with enhanced Hc1 can tolerate higher accelerating gradients, allowing for the construction of SRF particle accelerators with lower capital costs, and more stable beams and cryogenic systems. Multilayer films are composed of alternating layers of insulator and superconductor, each of which layer is thinner than the Loudon penetration depth of the superconductor. This dissertation presents an experimental program for the evaluation of multilayer thin films for SRF, as well as the first evaluation of such films in the RF regime. A stripline disk resonator operating at 2.8 GHz supplies field to a small, flat multilayer sample, in which the superconducting film is (Nb, Ti)N and the insulating film is Al 2O3. By measuring the Q of the resonator, Hc1 may be measured and compared with equivalent bulk superconducting samples. |
