Improving the performance of mid-T baked niobium cavities through post-bake surface treatment

TL;DR

This study improves niobium superconducting RF cavities by applying a surface treatment after medium-temperature baking, which enhances their quench field and quality factor by removing surface contaminants.

Contribution

It demonstrates that post-bake ultralight chemical surface removal significantly improves cavity performance by eliminating bake-induced surface residues.

Findings

Enhanced quench field after surface treatment

Increased quality factor (Q0) post-treatment

Evidence of surface contaminants affecting performance

Abstract

The Medium temperature (mid-T) baking of niobium superconducting radio-frequency cavities at 300 350  C in a vacuum furnace is known to enhance the quality factor (Q₀). However, despite this improvement, cavities treated with this process often exhibit premature quench at relatively low accelerating fields. This limitation is suspected to arise from the formation of surface contaminants, such as niobium carbides, during the furnace bake at 350 C for 3 h. To investigate the influence of potential surface contamination, this study applied an ultralight chemical removal to 1.3 GHz and 650 MHz single-cell cavities that had undergone medium-temperature baking. The removal of the top RF surface layer led to a notable improvement in the quench field and Q₀, indicating a beneficial effect of eliminating possible surface residues introduced during the bake.