Nonlinear Near-Field Microwave Microscope For RF Defect Localization in Superconductors

TL;DR

This paper introduces a nonlinear near-field microwave microscope using magnetic write head technology to identify localized defects in superconducting Nb surfaces, aiming to improve RF defect localization for accelerator applications.

Contribution

It presents a novel microwave microscopy technique employing magnetic write head technology to induce nonlinear effects for defect detection in superconductors.

Findings

Successfully induced nonlinear Meissner effect in superconductors

Achieved high RF magnetic fields (~200 mT) on submicron scales

Potential for high-resolution defect localization in Nb surfaces

Abstract

Niobium-based Superconducting Radio Frequency (SRF) cavity performance is sensitive to localized defects that give rise to quenches at high accelerating gradients. In order to identify these material defects on bulk Nb surfaces at their operating frequency and temperature, it is important to develop a new kind of wide bandwidth microwave microscopy with localized and strong RF magnetic fields. By taking advantage of write head technology widely used in the magnetic recording industry, one can obtain ~200 mT RF magnetic fields, which is on the order of the thermodynamic critical field of Nb, on submicron length scales on the surface of the superconductor. We have successfully induced the nonlinear Meissner effect via this magnetic write head probe on a variety of superconductors. This design should have a high spatial resolution and is a promising candidate to find localized defects on bulk Nb surfaces and thin film coatings of interest for accelerator applications.