Superconducting Nb3Sn cavities with high microwave qualities

As the lower critical flux density B
c1
apparently presents no limit for microwave superconductivity, Type II superconductors with a high transition temperature offer advantages over niobium, the material normally used for superconducting cavities. We have developed Nb
3
Sn cavities by exposing a Nb structure to a saturated tin vapour atmosphere at about 1000 °C. A report is given on the preparation of smooth and homogeneous Nb
3
Sn layers and on measurements on X-band cavities. At 4.2 K, Q-values up to 2.7 × 10
⁹
have been measured which are higher by a factor of seventy than for Nb resonators at the same temperature. Critical flux densities of 89 mT at 4.2 K and 106 mT at 1.5 K have been reached. With Nb
3
Sn cavities of this kind it would for the first time appear to be possible to operate superconducting cavities for technical applications at a temperature of 4.2 K. This would offer Considerable advantages.