Nitrogen and argon doping of niobium for superconducting radio frequency cavities: a pathway to highly efficient accelerating structures

TL;DR

This paper introduces a novel surface treatment involving nitrogen and argon doping of niobium, significantly enhancing the efficiency and reducing the cryogenic load of superconducting RF cavities beyond traditional limits.

Contribution

It demonstrates a new doping and electropolishing process that surpasses existing surface treatments, leading to unprecedented low microwave surface resistance in niobium cavities.

Findings

Surface resistance reduced beyond expected limits

Efficiency of accelerating structures improved up to 3 times

Reversal of field dependence of surface resistance

Abstract

We report a surface treatment that systematically improves the quality factor of niobium radio frequency cavities beyond the expected limit for niobium. A combination of annealing in a partial pressure of nitrogen or argon gas and subsequent electropolishing of the niobium cavity surface leads to unprecedented low values of the microwave surface resistance, and an improvement in the efficiency of the accelerating structures up to a factor of 3, reducing the cryogenic load of superconducting cavities for both pulsed and continuous duty cycles. The field dependence of the surface resistance is reversed compared to standardly treated niobium.