Design and operation of ACTPol, a millimeter-wavelength, polarization-sensitive receiver for the Atacama Cosmology Telescope

Séminaire IPAG de Benjamin Schmitt (University of Pennsylvania), jeudi 19 septembre 2013 à 11h00, IPAG seminar room

We discuss considerations for the design and characterization of ACTPol, a new millimeter-wavelength, polarization-sensitive receiver for the Atacama Cosmology Telescope (ACT). ACT is a six-meter telescope located in northern Chile, dedicated to enhancing our understanding of the structure and evolution of the universe through observations of the Cosmic Microwave Background (CMB) with arcminute resolution. We describe the design of the ACTPol focal plane at full deployment, consisting of dual 150 GHz array package modules and a multichroic array with simultaneous 90 GHz and 150 GHz sensitivity. Each of these detector array packages reside behind high-purity silicon reimaging optics with a novel anti-reflective coating geometry. Each array module consists of 1000 transition-edge sensor (TES) bolometers used to measure the response of 500 feedhorn-coupled polarimeters, enabling characterization of two orthogonal linear polarizations of the incident CMB radiation. The polarimeters are mechanically coupled to an octakaidecagonal, monolithic corrugated silicon feedhorn array and read-out via time-division SQUID multiplexing. The receiver is cooled using a custom-designed dilution refrigerator, providing a 100 mK bath temperature to the detectors, which have a target Tc of 150 mK. With first light achieved in July 2013, details of the ACTPol receiver deployment and early field testing will be highlighted.