Abstract
In order to minimize the surface resistance in superconducting cavities, a deeper understanding of residual resistance due to trapped magnetic flux is necessary. For that purpose, a combined temperature and magnetic field mapping system is employed to map magnetic flux trapped in a superconducting cavity, and the related increase in surface resistance. By cooling down a 1.3 GHz TESLA single cell cavity several times with externally applied static magnetic fields with different orientations with respect to the cavity, a statement can be made about how the angle between the applied magnetic field and the cavity's surface affects flux trapping, and surface resistance. For example, a significantly higher increase in surface resistance is observed when the applied magnetic field is perpendicular to the cavity's surface compared to when it is parallel.
Highlights
When operating superconducting cavities, power is dissipated within the cavity wall
A combined temperature and magnetic field mapping system is employed to map magnetic flux trapped in a superconducting cavity, and the related increase in surface resistance
The magnetic flux mapping, and the temperature mapping measurements where a top bottom asymmetry is observed, show that the flux trapping mechanism cannot be fully explained by a simple static model
Summary
Power is dissipated within the cavity wall. Since the cavities are operated at a temperature of around 2 K the wall plug power needed for 1 W of dissipated power is close to 1 kW [1]. The BCS surface resistance, RBCS, follows from the microscopic theory of superconductors as formulated by Bardeen, Cooper, and Schrieffer [2] It depends on the material used, its treatment as well as the operating temperature, and the frequency of the rf field. The second part of the surface resistance, residual resistance Rres, is not explained by BCS theory This resistance is temperature independent, and is mainly caused by trapped magnetic flux [3,4]. Materials contain defects, which pin flux lines, and prevent their expulsion from the superconductor In rf fields, these flux lines oscillate causing power to dissipate within the cavity wall which in turn increases the residual resistance [5,6]. We observe the largest increase in surface resistance where the trapped flux is perpendicular to the cavity’s surface
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
