The effect of vacancies on the microwave surface resistance of niobium revealed by positron annihilation spectroscopy

作者：Alexander Romanenko, C J Edwardson, P. G. Coleman, P. J. Simpson · 发表于：Applied Physics Letters · 年份：2013 · DOI：10.1063/1.4811090 · 被引用次数：31 · 研究领域：Superconducting and THz Device Technology、Particle accelerators and beam dynamics、Gyrotron and Vacuum Electronics Research

Using variable-energy positron annihilation spectroscopy, we demonstrate that a different near-surface vacancy concentration accompanies drastic differences in surface resistance of superconducting niobium cavities for particle acceleration. Our data suggest that vacuum baking at 120 °C leads to the doping of a near-surface layer with vacancy-hydrogen complexes, and that higher vacancy-type defect concentration distinguishes electropolished from chemically etched cavities. Our findings may help to explain a strong dependence of cavity performance on heat and chemical treatments, and may be of interest to other physics fields including cavity quantum electrodynamics (QED), microresonators, and single photon detectors.