On the field dependent surface resistance of niobium on copper cavities

Abstract

The surface resistance Rs of superconducting cavities prepared by sputter coating a thin niobium film on a copper substrate increases significantly stronger with the applied RF field compared to cavities of bulk material. A possible cause is that due to the thermal boundary resistance between the copper substrate and the niobium film Rs is enhanced due to global heating of the inner cavity wall. Introducing helium gas in the cavity and measuring its pressure as a function of applied field allowed to conclude that the inner surface of the cavity is heated up by only 60+/-60 mK when Rs increases with Eacc by 100 nOhm. This is more than one order of magnitude less than what one would expect from global heating. Additionally the effect of cooldown speed and low temperature baking have been investigated in the framework of these experiments. It is shown that for current state of the art niobium on copper cavities there is only a detrimental effect of low temperature baking. A fast cooldown results in a lowered Rs.

7 pages, 8 figures

References in corpus (1)

• Dependence of the residual surface resistance of superconducting RF cavities on the cooling dynamics around $T_{\mathrm{c}}$

Cited by in corpus (4)

• Two different origins of the Q-slope problem in superconducting niobium film cavities for a heavy ion accelerator at CERN
• A low energy muon spin rotation and point contact tunneling study of niobium films prepared for superconducting cavities
• Determination of the magnetic field dependence of the surface resistance of superconductors from cavity tests
• A model for hot spots and Q-slope in granular Niobium thin film superconducting RF cavities