A fully portable, cryocooler-based HTS SQUID NDE instrument
We have recently introduced a novel cryocooler-based HTS SQUID NDE instrument. The system incorporates a closed-cycle cooler that is connected to the inner and outer copper thermal batteries which then allows simultaneous cooling of both masses. Once the inner has been cooled to a temperature of approximately 40 K and the outer to a slightly higher temperature of around 70 K, the connecting "coldfinger" is retracted through a gate valve and the thermal batteries are then maintained in a sealed, vacuum-tight chamber. At this point, the cryocooler can be switched off and fully disconnected from the cryobattery. A sapphire rod is attached to one end of the inner copper thermal mass and this holds the HTS SQUID gradiometer mount. Here we report on the cooldown times for the system and discuss SQUID electrical characteristics at these lower temperatures. Finally we propose a design for the next generation of instrument.