Kugeler, Oliver; Vogt, Julia; Knobloch, Jens: Influence of the Couldown at the Transition Temperature on the SRF Cavity Quality Factor. In: Claire Antoine ... [Ed.] : SRF2013: Proceedings of the 16th International Conference on RF Superconductivity : September 23th to 27th 2013 in Cité Internationale Universitaire, Paris, FranceJACOW, 2014. - ISBN 978-3-95450-143-4, p. TUIOA01 / 370-373
http://accelconf.web.cern.ch/AccelConf/SRF2013/papers/tuioa01.pdf
Open Access Version
Abstract:
A significant improvement of the quality factor Q0 from values of 1.5×1010 to values around 3×1010 at 1.8 K has been repeatedly achieved in a fully dressed and horizontally operated TESLA type SRF cavity by limited thermal cycling, i.e. heating the cavity briefly above the 9.2 K transition temperature of niobium and subsequent cooling. Conceivable explanations for this effect include (a) changes in shielding efficacy of the magnetic shielding to (b) thermal currents to (c) hydrogen diffusion and hydride formation. Our experiments are inconsistent with (a) and (c) being the responsible mechanism. It appears that the generation of additional magnetic flux due to the thermoelectric effect and the flux dynamics near the transition temperature are responsible for the observed effect.