WP 6 Task 6 1 SQUID scanning W

WP 6 Task 6. 1 SQUID scanning W. Singer

We are in time in all positions

Task: Creating in cooperation with WSK a SQUID scanning system for Nb sheets of 265 x 265 mm (prototype for XFEL) Specification for SQUID scanning system should include: • XY table (aim rotating table) • high signal/noise ratio • compensation of lift off effect • rather fast scanning (5 -10 min/sheet) • vacuum holder of the sheet, keeping it flat

SQUID-based scanning system developed at company WSK

Eddy current principle

Principle of SQUID magnetometer o SQUID gradiometer system

An excitation coil produces eddy currents in the sample, whose magnetic field is detected by the SQUID. A compensation coil close to the SQUID cancels the excitation field at the SQUID.

DC SQUID Quantization of the flux in the SQUID

SQUID for the Nb sheet scanner

Cryostat with the SQUID amplifying electronics

Lock-in amplifier and eddy current generator

3 -axis scanning table with cryostat and control device

Suppressing of the Lift-Off effect Without Lift-Off correction The same after Lift-Off correction

Nb test sheet wit Ta inclusions NAA Neutron activation analysis image of the Nb test sheet Eddy current image of the Nb test sheet

Penetration depth, mm Frequency , k. Hz Penetration depth/frequency dependence for niobium

SQUID scanning of Nb test sheets

3 D image of Nb test sheet with artificial Ta defects by SQUID scanning

The End