Development of sensor SQUID and Zappe interferometer switch for HUBS

Hot Universe Baryon Surveyor ( HUBS) is a proposed Chinese space mission to search for the so-called "missing baryons". HUBS will focus on soft X-ray detection. The central part of the HUBS telescope is a soft X-ray spectrometer that uses a large transition-edge sensors array to detect the photon emission from a warm-hot intergalactic medium. The detector array comprises more than 3600 pixels. To read such a large number of pixels, a multiplexed readout technique is obligatory. We aim to develop a time-division multiplexed (TDM) readout system for HUBS. We choose TDM because it is the most mature and common one among various multiplexed readout techniques. We started by developing a proto-type TDM system that uses a single-stage SQUID readout. The basic multiplexing unit is composed of a SQUID series array (SSA) in parallel with a SQUID-based superconducting/normal conducting switch (SN switch). The SSA is composed of 16 individual SQUID cell that adopts a 1st order serial gradiometer design. The switch is also made of SQUID cells connected in series. The SQUID cell for a switch can comprise two Josephson junctions (JJs) like a usual DC-SQUID. It can also take the form of a Zappe interferometer that consists of four JJs. We will present the design and the simulation results of the sensor SQUID array and the SN switches.