Design of niobium-based mushroom-shaped cavity for critical magnetic field evaluation of superconducting multilayer thin films toward achieving higher accelerating gradient cavity

We designed a niobium-based mushroom-shaped cavity for evaluating the critical magnetic field of superconducting multilayer thin films. The distribution of the magnetic field strength at a radio frequency (RF) of 5.2 GHz was calculated in a sample region, and the maximum magnetic field strength at 1 W RF power in the cavity was calculated to be 60.0 kA m(-1) (75.4 mT). Subsequently, we tested the production of a miniature hemisphere cavity to confirm the accuracy of its curvature radius. We measured the slope profile of the hemisphere using a three-dimensional shape measurement system and evaluated the accuracy of fabrication. (C) 2019 The Japan Society of Applied Physics