Development of SQUID microscope for localization and imaging of material defects (NDE)

Dramatic progress was made in FY1997, the first full year of implementing a new technique for detecting and imaging material defects in nuclear weapon components. Design, fabrication, and initial tests of a ``SQUID Microscope`` has been completed utilizing the extraordinary sensitivity of High-Critical-Temperature (HTC) Superconducting QUantum Interference Device (SQUID) technology. SQUIDs, the most sensitive magnetic field detectors known, are used to sense magnetic anomalies caused by the perturbation of an induction field by defects in the material under examination. Time variation of the amplitude (A) and angle ({theta}) of an induction field with unique spatial distribution allows examination of material defects as a function of depth and orientation within the sample. Variation of the frequency of amplitude variation, {Omega}(A), enables depth selection in a given sample. Scanning the sample in physical, A, and {theta} space enables detection and localization of defects to high precision. A few examples of the material defects anticipated for study include cracks, stress fractures, corrosion, separation between layers, and material inclusions. Design and fabrication of a prototype SQUID Microscope has been completed during FY97. Extensive testing of the physical, thermal, precision mechanical, and vacuum performance of the SQUID microscope were performed. First preliminary tests of the integrated system have been performed and initial results were obtained in the first week of September 1997, more than 3 months ahead of schedule