Daniel Schwan, Peter A. R. Ade, Kaustuv Basu, Amy N. Bender, Frank Bertoldi, Hsaio-Mei Cho, Guyong. Chon, John Clarke, Matt Dobbs, Daniel Ferrusca, Rolfe Gusten, Nils W. Halverson, William L. Holzapfel, Cathy Horellou, Daniel Johansson, Bradley R. Johnson, James Kennedy, Zigmund Kermish, Ruediger Kneissl, Trevor Lanting, Adrian T. Lee, Martin Lueker, Jared Mehl, Karl M. Menten, Dirk Muders, Florian Pacaud, Thomas Plagge, Christian L. Reichardt, Paul L. Richards, Rienhold Schaaf, Peter Schilke, Martin W. Sommer, Helmuth Spieler, Carole Tucker, Axel Weiss, Benjamin Westbrook, Oliver Zahn
The Atacama pathfinder experiment Sunyaev-Zel'dovich (APEX-SZ) instrument is a millimeter-wave cryogenic receiver designed to observe galaxy clusters via the Sunyaev-Zel'dovich effect from the 12 m APEX telescope on the Atacama plateau in Chile. The receiver contains a focal plane of 280 superconducting transition-edge sensor (TES) bolometers instrumented with a frequency-domain multiplexed readout system. The bolometers are cooled to 280 mK via a three-stage helium sorption refrigerator and a mechanical pulse-tube cooler. Three warm mirrors, two 4 K lenses, and a horn array couple the TES bolometers to the telescope. APEX-SZ observes in a single frequency band at 150 GHz with 1' angular resolution and a 22' field-of-view, all well suited for cluster mapping. The APEX-SZ receiver has played a key role in the introduction of several new technologies including TES bolometers, the frequency-domain multiplexed readout, and the use of a pulse-tube cooler with bolometers. As a result of these new technologies, the instrument has a higher instantaneous sensitivity and covers a larger field-of-view than earlier generations of Sunyaev-Zel'dovich instruments. The TES bolometers have a median sensitivity of 890 uKcmb-sqrt(s) (NEy of 3.5e-4 sqrt(s)). We have also demonstrated upgraded detectors with improved sensitivity of 530 uKcmb-sqrt(s) (NEy of 2.2e-4 sqrt(s)). Since its commissioning in April 2007, APEX-SZ has been used to map 48 clusters. We describe the design of the receiver and its performance when installed on the APEX telescope.
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http://arxiv.org/abs/1008.0342
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