Evaluation of flux expulsion and flux trapping sensitivity of srf cavities fabricated from cold work Nb sheet with successive heat treatment

TL;DR

This study investigates how high-temperature heat treatments affect flux expulsion and trapping sensitivity in superconducting RF cavities made from cold-worked niobium, comparing their performance to standard fine-grain niobium cavities.

Contribution

It demonstrates that cold-worked niobium cavities exhibit improved flux expulsion after specific heat treatments, providing insights into optimizing superconducting cavity fabrication.

Findings

Cold-worked Nb cavities show better flux expulsion after 800°C/3h treatment.

Flux trapping sensitivity remains similar for higher temperature treatments.

RF performance correlates with flux expulsion and trapping behavior.

Abstract

The main source of RF losses leading to lower quality factor of superconducting radio-frequency cavities is due to the residual magnetic flux trapped during cool-down. The loss due to flux trapping is more pronounced for cavities subjected to impurities doping. The flux trapping and its sensitivity to rf losses are related to several intrinsic and extrinsic phenomena. To elucidate the effect of re-crystallization by high temperature heat treatment on the flux trapping sensitivity, we have fabricated two 1.3 GHz single cell cavities from cold-worked Nb sheets and compared with cavities made from standard fine-grain Nb. Flux expulsion ratio and flux trapping sensitivity were measured after successive high temperature heat treatments. The cavity made from cold worked Nb showed better flux expulsion after 800 C/3h heat treatments and similar behavior when heat treated with additional 900 C/3h and 1000 C/3h. In this contribution, we present the summary of flux expulsion, trapping sensitivity, and RF results.