Large Format X-Ray Magnetic Calorimeters with Multiplexed SQUID Readouts

An innovative large format cryogenic x-ray detector is described that is based on an array of magnetic microcalorimeters and fast, multiplexed SQUID readouts. The proposed microcalorimeter design consists of a thick-film x-ray absorber deposited on top of a paramagnetic alloy that is coupled to a sensitive dc SQUID. The energy deposited by incident radiation causes a temperature increase and subsequent change of the alloy magnetization, which is precisely measured by the SQUID. Owing to the unsurpassed flux sensitivity, high intrinsic bandwidth and low power dissipation of dc SQUIDs, these devices are ideally suited to read out magnetic calorimeters. A novel sequential readout scheme is used to multiplex the outputs, which greatly reduces the thermal heat load of the SQUIDs and the number of wires to the room-temperature electronics. The innovative magnetic microcalorimeter and multiplexed SQUID readout designs to be completed during Phase I and fabricated during Phase II will offer improved performance over current generation designs. These detectors will especially be useful for applications requiring large format arrays of x-ray calorimeters, such for NASA missions and astrophysics research as well as commercial microanalysis systems.