Plasma cleaning: A new possible treatment for niobium superconducting cavity after nitrogen doping

TL;DR

This study explores plasma cleaning with argon and oxygen gases as a novel method to remove surface contaminants from niobium superconducting cavities post-nitrogen doping, potentially improving performance without hydrogen reintroduction.

Contribution

The paper introduces plasma cleaning as a new treatment for niobium cavities after nitrogen doping, effectively reducing impurities without hydrogen contamination.

Findings

Plasma cleaning reduces impurity elements in niobium surface by about 30 nm depth.

It does not introduce hydrogen, unlike electropolishing.

Optimal conditions are around 20Pa and 100W power.

Abstract

Nitrogen doping treatment with the subsequent electropolishing (EP) of the niobium superconducting cavity can significantly increase the cavity's quality factor up to a factor of 3. But the process of the EP removal may reintroduce hydrogen in the cavity surface, which may influence the cavity's radio frequency performance. Plasma cleaning study on niobium samples with gas mixtures of argon and oxgen intended to remove contaminations (hydrocarbons and micronicdust particles) from cavity surface to avoid field emission, was performed in Peking University. The niobium samples have been analyzed using the time of flight secondary ion mass spectrometry (TOF-SIMS) to measure the depth profiles of H, C, O, F, P and Nb. The measuring results show that the plasma cleaning with gas mixtures of argon and oxgen and conditions of about 20Pa and 100W can remarkably reduce the contents of impurity elements in the depth of about 30 nm without introducing hydrogen in the cavity surface. So plasma cleaning has been proposed to be a new possible treatment for niobium superconducting cavity after nitrogen doping.