Evaluating the multi-layer thin-film superconductor using the third harmonic voltage method

In recent years, it is pointed out that the maximum accelerating gradient of the superconducting cavities can be increased more by coating inner surfaces with multilayer-thin film superconductor. In the method, critical magnetic field, Hc1, is a principal parameter to achieve the sufficient performance. We therefore constructed a system to measure critical magnetic field of superconductive material using the third harmonic voltage method. In this paper, we will report on the current status of the system and preliminary results. (author)