Digital SQUID Magnetometers for Read-out of Detectors and Magnetic Particles

Detectors utilized in high energy and nuclear physics research, have, historically, been instrumented with FET amplifiers operated in the cryogenic environment. These amplifiers require heated operation and suffer from large 1/f noise, are very sensitive to microphonic pickup, and dissipate high power. More recently, analog SQUIDs (Superconducting QUantum Interference Devices) have replaced FETs and have solved all of the problems associated with FETs. However, analog SQUIDs are extremely sensitive to magnetic fields and in their present configuration are not suitable when large fields are present. In certain cases, such as measurements of atomic and nuclear collisions reaction dynamics, quantum computation applications, and nuclei polarization for certain medical imaging, should be performed in unshielded environments and/or in presence of a field. The objective of this program is to develop multiplexed ultra-low noise digital SQUID magnetometers for detecting magnetization of polarized nuclei in a magnetic field as well as read-out of detectors in unshielded environments. The proposed SQUID magnetometer integrates a SQUID with a superconducting antenna, which consists of two highly balanced loops rejecting large uniform fields. One of the loops is utilized to couple to detectors or to magnetically polarized beams. The pickup loops are fabricated on the same cryogenic chip as the SQUID to allow highly balanced loops. Alternatively, superconducting wires can be utilized to fabricate large pickup loops if such loops cannot be accommodated on substrates using thin film technology. The novel SQUID magnetometer chips will be inexpensive, ultra-low noise, and can be easily instrumented with simple electronics. In addition, since superconductive devices are radiation-resistant, the SQUIDs are well-suited for applications in particle accelerator environments. Commercial Applications and Other Benefits: The availability of a low-cost multi-channel SQUID system would result in their wide-spread use in high-resolution x-ray spectroscopy, detector array imaging, particle identification systems, electron microscope systems for material surface characterization studies, medical imaging, and non-destructive evaluation.