The FDM readout system for the TES bolometers of the SWIPE instrument on the balloon-borne LSPE experiment

We present the design and first tests of a prototype readout for the SWIPE instrument onboard the LSPE balloon-borne experiment. LSPE aims at measuring the linear polarization of the Cosmic Microwave Background (CMB) at large angular scales, to find the imprint of inflation on the B-mode CMB polarization. The SWIPE instrument hosts two focal planes hosting 163 TES Au/Mo spiderweb bolometers each, cooled at 0.3 K for the detection of microwave frequencies of 140, 220 and 240 GHz. To read all the detectors, a 16 channel frequency domain multiplexing readout system has been devised, consisting of LC resonators composed of custom Nb superconducting inductors and commercial SMD capacitors. A set-up consisting of 14 LC resonators shows that we can accommodate 16 channels in the frequency range between 200 kHz and 1.6 MHz, since the necessary line-widths can be achieved. A preliminary firmware for the generation and read-out of the biasing frequency comb is also discussed.