Analog SQUID magnetometers with additional positive feedback for magnetic beam measurement

The magnetization of polarized nuclei can be determined by using analog DC SQUID (Superconducting QUantum Interference Device) magnetometers. When a large number of channels (>10) are needed for imaging, multiplexed digital SQUIDs that integrate analog SQUIDs with on-chip digital processing circuits, can be utilized and then instrumented with simple peripheral electronics facilitating data acquisition. However, applications requiring few read-out channels are better served with analog SQUIDs. In order to utilize a conventional analog DC SQUID, its voltage is amplified by a step-up transformer and its transfer characteristics is linearized so it could be instrumented with room temperature electronics. The amplification and linearization limits the system bandwidth and require extensive peripheral electronics. A novel analog SQUID is proposed to be developed, which completely eliminates the extensive peripheral electronics and will integrate the SQUID with a superconducting pick- up coil for single-channel systems. An Additional Positive Feedback (APF) coil is incorporated on chip with the analog SQUID, which increases the gain of the device substantially, and as a result no step-up transformer and linearization electronics are required for read out. This additional positive feedback enhances the output voltage gain of the SQUID and enables the use of a direct read-out, circumventing the conventional modulation scheme and increasing the bandwidth more than one order of magnitude to 1 MHz. The objective of the proposed research is to develop high-sensitivity, thin-film low-temperature superconductive SQUID magnetometers with additional positive feedback and integrated pick-up loops in a highly sophisticated cryostat system. The magnetometer will be optimized for measurement of the magnetization of polarized nuclei in a magnetic field for measuring beam currents at the scale of 50 m to 1 mm. Hypres will design an APF SQUID with the goal of getting a SQUID magnetometer with adequate gain so it can be instrumented with simple peripheral electronics without the need for step-up transformer and lock-in amplification. The proposed work will develop a SQUID magnetometer with optimum field sensitivity for specific applications such as nuclear physics instrumentation and general applications, which require higher-sensitivity SQUID magnetometers and gradiometers but lower spatial resolution. SQUIDs are extremely sensitive magnetometers, which can be adapted for many applications such high energy and nuclear physics applications as well as sensors for biomedical applications and corrosion and cracks in metals. The proposed magnetometer system is compact and cost-effective facilitating its use in many research centers and laboratories. Commercial Applications and Other Benefits: The magnetometer system with the new advanced APF SQUID allows Hypres to extend its capabilities and establish the instrumentation techniques required for a rapid-cycle commercial capability to design, fabricate, and characterize custom, low-noise, integrated thin film SQUID magnetometers and gradiometers for high energy and nuclear physics instrumentation. Upon completion of this program, the instruments will be capable of making measurements impossible with any other technique. In addition, the new instrument as a biomagnetometer should lead to new insights into cellular biology and electro- and magnetophysiology. As they are developed, these SQUID chips will be incorporated immediately into the instrument for research and will be made available to others. The instrument will be sufficiently compact and inexpensive for investigators.