IMPROVEMENTS OF SUPERCONDUCTING CAVITY PERFORMANCES AT HIGH ACCELERATING GRADIENTS

A moderate heating (170°C 70 hours), under vacuum, modifies the Niobium cavity features: · at 4.2 K the BCS resistance is reduced by 46%, · at 1.5 K the high field Qo(Eacc) slope is smoothed off with an unchanged residual resistance value. This is a very attractive effect for the high gradient quest. These modifications are induced by the electron mean free path shortening, due to an oxygen diffusion into the superconducting material. In agreement with these results we develop a hypothesis about the Qo(Eacc) slope that take into account the NbO x superconducting layer and the magnetic field dependence on the energy gap.