Ac losses in field-cooled type I superconducting cavities

Abstract

As superconductors are cooled below their critical temperature, stray magnetic flux can become trapped in regions that remain normal. The presence of trapped flux facilitates dissipation of ac current in a superconductor, leading to losses in superconducting elements of microwave devices. In type II superconductors, dissipation is well-understood in terms of the dynamics of vortices hosting a single flux quantum. In contrast, the ac response of type I superconductors with trapped flux has not received much attention. Building on Andreev's early work [Sov. Phys. JETP 24, 1019 (1967)], here we show theoretically that the dominant dissipation mechanism is the absorption of the ac field at the exposed surfaces of the normal regions, while the deformation of the superconducting/normal interfaces is unimportant. We use the developed theory to estimate the degradation of the quality factors in field-cooled cavities, and we satisfactorily compare these theoretical estimates to the measured field dependence of the quality factors of two aluminum cavities.

9 pages, 3 figures

References in corpus (4)

• Ultra-high quality factors in superconducting niobium cavities in ambient magnetic fields up to 190 mG
• Microwave response of thin niobium films under perpendicular static magnetic fields
• Theoretical estimates of maximum fields in superconducting resonant radio frequency cavities: Stability theory, disorder, and laminates
• Strong reduction of field-dependent microwave surface resistance in YBa${}_2$Cu${}_3$O${}_{7-\delta }$ with sub-micrometric BaZrO${}_3$ inclusions

Cited by in corpus (1)

• Tuning microwave losses in superconducting resonators