Excellent performance of 650 MHz single-cell niobium cavity after electropolishing

TL;DR

This study demonstrates that optimized electropolishing significantly enhances the performance of 650 MHz single-cell niobium cavities, achieving the highest gradient for this cavity type.

Contribution

The paper reports the first achievement of a 53.3 MV/m gradient in a 650 MHz single-cell niobium cavity using optimized electropolishing techniques.

Findings

Achieved a maximum gradient of 53.3 MV/m at 2 K.

Cavities showed smooth surfaces and good baseline performance.

Electropolishing modifications improved cavity performance.

Abstract

Electropolishing process and cathodes have undergone modification and optimization for both low- and high-beta 650 MHz five-cell niobium cavities for PIP-II. Cavities treated with these modified electropolishing conditions exhibited smooth surfaces and good performance in baseline tests. Nonetheless, due to administrative constraints on project cavities, maximum gradient performance testing was not conducted. This paper presents a study conducted on a single-cell 650 MHz cavity utilizing the optimized electropolishing conditions, highlighting the maximum performance attained for this specific cavity. The cavity tested at 2 K in a vertical cryostat reached a superior accelerating field gradient of 53.3 MV/m at Q0 of 1.6x1010, which is the highest gradient attained for this type of large-sized cavities.