Flux Expulsion and Material Properties of Niobium Explored in 644-650 MHz Cavities

TL;DR

This study investigates how different niobium materials and heat treatments affect magnetic flux expulsion in 644-650 MHz cavities, aiming to improve high-Q cavity performance for future projects.

Contribution

It compares flux expulsion efficiency of niobium from two vendors and links material properties to flux expulsion, enabling better prediction and optimization of cavity treatments.

Findings

High-temperature annealing and fast-cooldowns improve flux expulsion.

Material properties vary between vendors, affecting flux expulsion.

Potential to predict flux expulsion based on material analysis.

Abstract

Upcoming projects requiring high-Q ~650 MHz medium-to-high-${\beta}$ elliptical cavities drive a need to understand magnetic RF loss mechanisms and mitigations in greater detail. High-temperature annealing and fast-cooldowns have proven effective techniques for promoting magnetic flux expulsion in cavities, however the extent of their effectiveness has been observed to vary between niobium material lot and vendor. We explore the fast-cooldown method, and high-temperature annealing (900{\deg}C) in 644-650 MHz cavities fabricated from two different niobium vendors: Tokyo-Denkai, and Ningxia. which promote flux-expulsion efficiency. Using EBSD and PPMS methods, we aim to trace cavity flux expulsion efficiency to specific, measurable properties of the bulk niobium material, which, if identified, can lead to methods by which the flux expulsion properties of Nb material can be predicted prior to cavity fabrication, and can enable fine-tuning of cavity temperature treatments.