Temperature, RF Field, and Frequency Dependence Performance Evaluation of Superconducting Niobium Half-Wave Cavity

TL;DR

This study investigates how temperature, RF field, and frequency affect the performance of superconducting niobium half-wave cavities, focusing on surface resistance and quality factor improvements through impurity doping and surface treatments.

Contribution

It provides experimental RF measurements of niobium cavities across various frequencies, temperatures, and fields, enhancing understanding of surface resistance dependencies.

Findings

Surface resistance decreases with impurity doping and surface treatment.

Quality factor increases with higher accelerating gradients.

Surface resistance varies with frequency, temperature, and RF field.

Abstract

Recent advancement in superconducting radio frequency cavity processing techniques, with diffusion of impurities within the RF penetration depth, resulted in high quality factor with increase in quality factor with increasing accelerating gradient. The increase in quality factor is the result of a decrease in the surface resistance as a result of nonmagnetic impurities doping and change in electronic density of states. The fundamental understanding of the dependence of surface resistance on frequency and surface preparation is still an active area of research. Here, we present the result of RF measurements of the TEM modes in a coaxial half wave niobium cavity resonating at frequencies between 0.3-1.3 GHz. The temperature dependence of the surface resistance was measured between 4.2 K and 1.6 K. The field dependence of the surface resistance was measured at 2.0 K. The baseline measurements were made after standard surface preparation by buffered chemical polishing.