Impact of medium temperature heat treatment on flux trapping sensitivity in SRF cavities

TL;DR

This study investigates how mid-temperature heat treatments (150-400°C) affect flux trapping sensitivity in 1.3 GHz SRF cavities, revealing increased sensitivity at higher treatment temperatures and their impact on cavity performance.

Contribution

It provides new insights into the relationship between heat treatment temperature and flux trapping sensitivity in SRF cavities, which was not thoroughly characterized before.

Findings

Sensitivity increases with heat treatment temperatures between 200-325°C.

Higher treatment temperatures correlate with changes in electromagnetic response.

Variations in penetration depth and quasi-particle density influence cavity performance.

Abstract

The effect of mid-T heat treatment on flux trapping sensitivity was measured on several 1.3 GHz single cell cavities subjected to vacuum annealing at temperature of 150 - 400 $^\circ$C for a duration of 3 hours. The cavity was cooldown with residual magnetic field $\sim$0 and $\sim$20 mG in the Dewar with cooldown condition of full flux trapping. The quality factor as a function of accelerating gradient was measured. The results show the correlation between the treatment temperature, quality factor, and sensitivity to flux trapping. Sensitivity increases with increasing heat treatment temperatures within the range of (200 - 325 $^\circ$C/3h). Moreover, variations in the effective penetration depth of the magnetic field and the density of quasi-particles can occur, influencing alterations in the cavity's electromagnetic response and resonance frequency.