Superconducting Nb3Sn-cavities

Microwave critical magnetic flux densities B
c
^ac
up to 160 mT and higher than B
c1
were obtained with niobium-cavities by special surface treatments. Breakdown in this flux density region occurs by a thermal breakdown mechanism in which no superconducting critical flux density is involved. Considerable increase in B
c
^ac
may be expected with high-T
c
-superconductors such as Nb
3
Sn. Nb
3
Sn-layers were produced on niobium structures by exposing them to a saturated Sn-vapour at 1000 °C. B
c
^ac
-values up to 40 mT and surface resistances smaller than 10
^-6
Ω were measured with TE
011
-cavities at 9.5 GHz.