IMPROVEMENTS OF SUPERCONDUCTING CAVITY PERFORMANCES
AT HIGH ACCELERATING GRADIENTS
B. Visentin, J.P. Charrier, B. Coadou, CEA, Saclay, France
( paper presented at the Poster Session TUP07B - EPAC'98 - 22/26 June 1998 - Stockholm )
Abstract
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 NbOx superconducting layer and the magnetic field dependence on the energy gap.
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