Thermal design and control of Athena Wide Field Imager (WFI) camera head

The Wide Field Imager (WFI) is one of two instruments on the ATHENA (Advanced Telescope for High-ENergy Astrophysics) X-ray space telescope. The WFI features a camera head comprising a large detector array with a readout time of less than 5 ms and a fast detector with a readout time of 80 μs. The large detector array consists of four quadrants and each quadrant houses a sensor with a matrix of 512 × 512 pixels of Depleted P-channel Field Effect Transistors (DEPFET) with a pixel size of 130 μm. The fast detector comprises a sensor with 64×64 pixels, using the same technology and pixel size as the large detector. Both sensors are controlled and read out by the frontend electronics (FEE), which consists of two types of application specific integrated circuits (ASIC) mounted close to the DEPFET sensors.

The DEPFET sensors operate at temperatures between 193 K and 213 K, dissipating less than 1 W per LD. In contrast, the frontend electronics operate at a higher temperature, requiring approximately 10 W per large detector. The proximity of the ASICs and the DEPFET sensor for electrical performance necessitates a complex thermal design, decoupling the cooling chains for the DEPFET and the FEE.