Two different origins of the Q-slope problem in superconducting niobium film cavities for a heavy ion accelerator at CERN

A. Miyazaki; W. Venturini Delsolaro

doi:10.1103/PhysRevAccelBeams.22.073101

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Two different origins of the Q-slope problem in superconducting niobium film cavities for a heavy ion accelerator at CERN

A. Miyazaki, W. Venturini Delsolaro

DOI 10.1103/PhysRevAccelBeams.22.073101 · Physical Review Accelerators and Beams

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Abstract

Superconducting niobium film cavities deposited on copper substrates (Nb/Cu) have suffered from strong field-dependent surface resistance, often referred to as the Q-slope problem, since their invention. We argue that the Q-slope may not be an intrinsic problem, but rather originates from a combination of factors which can be revealed in appropriate environmental conditions. In this study, extrinsic effects were carefully minimized in a series of experiments on a seamless cavity. The origin of the Q-slope in low frequency cavities is traced back to two contributions with different temperature and magnetic field dependences. The first component of Q-slope, affecting the residual resistance, is caused by trapped magnetic flux which is normally suppressed by a magnetic shield for bulk niobium cavities. The second, temperature dependent component of Q-slope, is similar to the medium-field Q-slope which is well known in bulk niobium cavities. These results are compared with theoretical models and possible future studies are proposed.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	9.5	Pressure not reported	unknown