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HEPL / KIPAC Seminar

Thursday, December 4, 2014

Benjamin Schmitt

University of Pennsylvania

Design, integration, and first-season operation of ACTPol: A millimeter-wavelength, polarization-sensitive receiver for the Atacama Cosmology Telescope

Abstract:  We highlight considerations for the design and operation of ACTPol, a new receiver for the Atacama Cosmology Telescope (ACT), capable of making polarization-sensitive, millimeter-wavelength observations of the Cosmic Microwave Background (CMB) at arcminute angular scales.

ACT is a six-meter telescope located in northern Chile, dedicated to enhancing our understanding of the structure and evolution of the early Universe by direct measurement of the CMB. We describe the design of the ACTPol focal plane at fulldeployment, consisting of dual 150 GHz array package modules and a multichroic array package with simultaneous 90 GHz and 150 GHz sensitivity. Each of these detector array packages reside behind a set of custom-designed, high-purity silicon reimaging optics with a novel anti-reflective coating geometry, the characteristics of which will be detailed.

Each array package module consists of ~1000 transition-edge sensor (TES) bolometers used to measure the response of ~500 feedhorn-coupled polarimeters, enabling characterization of the linear orthogonal polarization of incident CMB radiation. The polarimeters are arranged in three hexagonal and three semi-hexagonal silicon wafer stacks, mechanically coupled to an octakaidecagonal, monolithic corrugated silicon feedhorn array (~140 mm diameter). Readout of the TES polarimeters is achieved using time-division SQUID multiplexing. Each array package is cooled using a custom-designed dilution refrigerator providing a sub-100 mK bath temperature to the detectors, which have a target Tc of 150 mK.

Given the unique cryomechanical constraints associated with this large-scale monolithic superconducting focal plane, we address the design considerations necessary for integration with the optical and cryogenic elements of the ACTPol receiver. With first light achieved in July 2013 with the first of three polarimeter arrays, and second season operations underway (operating with two 150GHz polarimeter arrays), details of the ACTPol receiver deployment and early polarization results will be highlighted, as well as the outlook for full-deployment operations, projected to begin in early-2015.

Finally, consideration will be given to allied-field applications of the distributed portfolio of ACTPol receiver technologies, as well as work underway toward the realization of Advanced ACTPol, a nextgeneration receiver for ACT, with the enhanced capability to measure large-angular-scale regimes to probe inflationary cosmology.

Time: 4:00 – 5:00pm

Location: Physics/Astrophysics Bldg., Kistler Conference Rooms 102/103 (Map)

(Light refreshments available 4:00pm; Presentation begis 4:15pm)

Open to All