Institute Science and Technology of Accelerating Systems

TraMaFlu

Characterization of flux trapping in superconductors

The TraMaFlu cryostat with Helmholtz coils to generate an arbitrary magnetic field in 3D.

When SRF cavities are cooled to the superconducting state, a fraction of the ambient magnetic field (e.g., the earth's magnetic field) may be trapped in the superconductor. This trapped flux can significantly increase the power dissipation of the SRF cavities. To understand the underlying mechanism of how magnetic flux is trapped and what treatments and operating conditions can reduce the flux-trapping efficiency BE-IAS operates MagFlux. It enables a systemic investigation of flux trapping by providing independent control of cooldown conditions which might have an influence on flux trapping: temperature gradient across the superconductor during cooldown, cooldown rate, and ambient magnetic field. MagFlux is unique in enabling quick thermal cycling, permitting up the analysis of up to 300 superconducting transitions in one day. 

Capabilities

• Sample size: 10 x 5 cm²

• Measure 3D trapped flux with better than 100 nT at 15 locations simultaneously

• Full control of the temperature gradient during the superconducting transition

• Full control of the cooldown rate through the superconducting transition

• Full control of the applied external 3D magnetic field up to 200 µT.

• Rapid cycling through Tc for multiple trapped-flux measurements

Measurement of trapped flux versus temperature gradient in niobium.

Schematic of TraMaFlu in the cryostat.