FCC Week 2016

Trapped Flux Dissipation in SRF Cavities

13 Apr 2016, 17:30

2h

Italy

Poster Superconducting RF Poster session

Speaker

Martina Martinello (Fermilab - IIT)

Description

Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. Indeed, one of the main contribution at the surface resistance of SRF cavities is the trapped flux surface resistance. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of flux trapped, depends on the cavity surface treatments, i.e. on the mean free path. A variety of 1.3 GHz cavities with different surface treatments (EP, BCP, 120C bake and different level of N-doping) were studied in order to cover the largest range of mean free path nowadays achievable, from few to thousands of nanometers. A bell shaped trend appears for the range of mean free path studied. Over doped cavities falls at the maximum of trapped flux sensitivity, while lighter doped cavities show sensitivity closer to EP cavity. It was also found that the trapped flux sensitivity has a field dependence which also depends on the surface treatment. EP cavities seems to have the larger field dependence leading to values of sensitivity comparable of N-doped cavities at high field.