In Situ Time Constant and Optical Efficiency Measurements of TRUCE Pixels in the Atacama B-Mode Search

The Atacama B-mode Search (ABS) instrument, which began observation in February of 2012, is a crossed-Dragone telescope located at an elevation of 5,100 m in the Atacama Desert in Chile. The primary scientific goal of ABS is to measure the B-mode polarization spectrum of the Cosmic Microwave Background from multipole moments of about ≈ 50 to ≈ 500 (angular scales from ∼0.4◦ to ∼4◦), a range that includes the primordial B-mode peak from inflationary gravitational waves. The ABS focal plane array consists of 240 pixels designed for observation at 145 GHz by the TRUCE collaboration. Each pixel has its own individual, single-moded feedhorn and contains two transition-edge S. M. Simon (B) · A. Kusaka · L. A. Page · L. P. Parker · J. L. Sievers · S. T. Staggs · K. Visnjic Department of Physics, Princeton University, Princeton, NJ 08544, USA e-mail: [email protected] J. W. Appel · T. Essinger-Hileman Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA H. M. Cho · K. D. Irwin National Institute of Standards and Technology, Boulder, CO 80305, USA K. D. Irwin Department of Physics, Stanford University, Stanford, CA 94305, USA M. D. Niemack Department of Physics, Cornell University, Ithaca, NY 14853, USA M. R. Nolta The Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada S. Raghunathan Department of Astronomy, Universidad de Chile, Santiago, Chile