Progress in the Development of Frequency‑Domain Multiplexing for the X‑ray Integral Field Unit on Board the Athena Mission

Abstract

Frequency-domain multiplexing (FDM) is the baseline readout system for the X-ray Integral Field Unit on board the Athena mission. Under the FDM scheme, TESs are coupled to a passive LC flter and biased with alternating current (AC bias) at MHz frequencies. Using high-quality-factor LC flters and room-temperature electronics developed at SRON and low-noise two-stage SQUID amplifers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. We have achieved a performance requested for the demonstration model with the single-pixel AC bias (ΔE = 1.8 eV) and nine-pixel multiplexing (ΔE = 2.6 eV) modes. We have also demonstrated 14-pixel multiplexing with an average energy resolution of 3.3 eV, which is limited by nonfundamental issues related to FDM readout in our laboratory setup.