EBEX was a long-duration balloon-borne experiment to measure the polarization of the cosmic microwave background. The experiment had three frequency bands centered at 150, 250, and 410 GHz and was the first to use a kilopixel array of transition edge sensor bolometers aboard a balloon platform. We describe the design and characterization of the array and the readout system. From the lowest to highest frequency, the median measured detectors' average thermal conductances were 39, 53, and 63 pW/K, the medians of transition temperatures were 0.45, 0.48, and 0.47 K, and the medians of normal resistances were 1.9, 1.5, and 1.4 Ω; we also give the measured distributions. With the exception of the thermal conductance at 150 GHz, all measured values are within 30% of their design. We measure median low-loop-gain time constants τ 0 = 88, 46, and 57 ms. Two measurements of bolometer absorption efficiency gave results consistent within 10% and showing high (∼0.9) efficiency at 150 GHz and medium (∼0.35 and ∼0.25) efficiency at the two higher bands. We measure a median total optical power absorbed of 3.6, 5.3, and 5.0 pW. EBEX pioneered the use of the digital version of the frequency domain multiplexing system. We multiplexed the bias and readout of 16 bolometers onto two wires. The median per-detector noise-equivalent temperatures are 400, 920, and 14,500 . We compare these values to our preflight predictions and to a previous balloon payload. We discuss the sources of excess noise and the path for a future payload to make full use of the balloon environment.
Bibliographical noteFunding Information:
Support for the development and flight of the EBEX instrument was provided by NASA grants NNX12AD50G, NNX13AE49G, NNX08AG40G, and NNG05GE62G and by NSF grants AST-0705134 and ANT-0944513. We acknowledge support from the Italian INFN INDARK Initiative. P.A. and G.S.T. acknowledge the Science & Technology Facilities Council for its continued support of the underpinning technology for filter and wave plate development. We also acknowledge support by the Canada Space Agency, the Canada Research Chairs Program, the Natural Sciences and Engineering Research Council of Canada, the Canadian Institute for Advanced Research, the Minnesota Supercomputing Institute, the National Energy Research Scientific Computing Center, the Minnesota and Rhode Island Space Grant Consortia, our collaborating institutions, and Sigma Xi, The Scientific Research Society. Research described in this paper used facilities of the Midwest Nano Infrastructure Corridor (MINIC), a part of the National Nanotechnology Coordinated Infrastructure (NNCI) program of the National Science Foundation. C.B. acknowledges support from the RADIO-FOREGROUNDS grant of the European Unionʼs Horizon 2020 research and innovation program (COMPET-05-2015, grant agreement no. 687312). J.D. acknowledges a NASA NESSF fellowship NNX11AL15H. B.R.-K. acknowledges an NSF Post-Doctoral Fellowship AST-1102774 and a NASA Graduate Student Research Fellowship. K.R. and K.Z. acknowledge support by the Minnesota Space Grant Consortium. The Flatiron Institute is supported by the Simons Foundation. S.M.F. was partially supported by the UK Science and Technology Facilities Council (STFC). We very much thank Danny Ball and his colleagues at the Columbia Scientific Balloon Facility for their dedicated support of the EBEX program. We thank Darcy Baron and Kaori Hattori for inputs on the stray inductance of the microstrips and an anonymous referee for his/her careful and thoughtful review.
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- cosmic background radiation
- cosmology: observations
- instrumentation: detectors
- instrumentation: polarimeters