cOperation of a High-T SQUID Gradiometer by Use of a Pulse Tube Refrigerator

Publisher Summary To test the applicability of a pulse tube refrigerator (PTR) for low-noise cooling, this chapter constructs a coaxial doubleinlet PTR designed for operation of a high-T c SQUID gradiometer which consists of two YBCO RF-SQUIDs. It is designed for cooling a YBCO RF-SQUID gradiometer. Reduction of interference signals from the pressure-wave generating rotary valve is accomplished by connecting the refrigerator inlets and the rotary valve via a long flexible tube. The cooler has been successfully employed to operate the gradiometer without any magnetic shielding. As a remaining source of weak periodic interference signals at the cold head, pressure-wave induced vibrations of the sensors in an ambient magnetic field can be identified. Corresponding improvements of the cooler are shown to give a still better performance of the SQUID gradiometer.