Design and preliminary results from a high temperature superconducting SQUID milliscope used for non-destructive evaluation

We present the design and preliminary results from a SQUID \´milliscope\´. The device was designed for nondestructive evaluation (NDE) as part of the Enhanced Surveillance Program at Los Alamos National Laboratory. A high temperature superconducting (RTS) SQUID sensor is used to map magnetic fields induced in the sample. Eddy currents are induced in the conducting sample by a wire coil designed to produce minimal magnetic field at the SQUID when no sample is present. The features of interest are characterized by anomalies in the induced magnetic field. The goal of the instrument is sensitivity to small features generally buried under several intervening layers (/spl sim/1-20 mm) of conducting and/or nonconducting materials and robustness of design (i.e. the ability to operate in a noisy, unshielded environment). The device has primarily focussed on specific NDE problems such as the ability to detect buried "seams" in conducting materials and quantify the width of these seams. We present the design of the instrument, and some data to demonstrate its capabilities.