The Simons Observatory: Magnetic Sensitivity Measurements of Microwave SQUID Multiplexers

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which observe from the Atacama Desert in Chile. In total, SO field ~70,000 transition-edge sensor (TES) bolometers six spectral bands centered between 27 280 GHz order to achieve sensitivity necessary measure or constrain numerous cosmological quantities. Universal Focal Plane Modules (UFMs) each contain 150 mm diameter TES detector array, horn lenslet optical coupling, cold readout components, magnetic shielding. use SQUID multiplexing (?MUX) at an initial factor of ~1000; (100 mK) components are packaged ?MUX module, is part UFM, can also characterized independently. 100 mK stage bolometer arrays SQUIDs sensitive fields, their measured response vary degree they magnetically shielded. We present measurements pickup test multiplexers as study various shielding configurations for Observatory. discuss how these motivated material choice design UFM