Effect of Low Temperature Baking in Nitrogen on the Performance of a Niobium Superconducting Radio Frequency Cavity

TL;DR

This study investigates how low temperature nitrogen baking affects the performance of niobium superconducting RF cavities, showing increased quality factors and specific surface chemistry changes without degrading superconducting properties.

Contribution

It demonstrates that low temperature nitrogen baking at 120-140°C enhances cavity quality factor similarly to high temperature doping, with detailed surface analysis and no adverse effects on superconductivity.

Findings

Increased quality factor observed after nitrogen baking at 120-140°C.

Surface analysis revealed complex Nb oxides and nitrides formation.

No significant change in bulk superconducting properties.

Abstract

We report the rf performance of a single-cell superconducting radiofrequency cavity after low temperature baking in a nitrogen environment. A significant increase in quality factor has been observed when the cavity was heat treated in the temperature range of 120-160 {\deg}C with a nitrogen partial pressure of ~25 mTorr. This increase in quality factor as well as the Q-rise phenomenon (anti-Q-slope) is similar to those previously obtained with high temperature nitrogen doping as well as titanium doping. In this study, a cavity N2-treated at 120 {\deg}C and at140 {\deg}C, showed no degradation in accelerating gradient, however the accelerating gradient was degraded by 25 with a 160 {\deg}C N2 treatment. Sample coupons treated in the same conditions as the cavity were analyzed by scanning electron microscope, x-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a complex surface composition of Nb_2O5, NbO and NbN(1-x)Ox within the rf penetration depth. Furthermore, magnetization measurements showed no significant change on bulk superconducting properties.