Alexander Cluff with John Ruhl
Creating an “on-sky” test environment for CMB detector arrays
Measuring Cosmic Microwave Background Radiation polarization anisotropies requires that detectors be held at extremely low temperatures (~.3K) in order to prevent noise. Cooling detectors to such temperatures in the laboratory is not a difficult task, but in order to perform “on-sky” tests of detectors we need to recreate the photon loading of the fairly transparent atmosphere through which the detectors look. My project is to design and create a blackbody load to be held at 5-10K that will be held above the detector arrays in a lab cryostat, recreating proper detector conditions. One limiting factor in such testing is the time it takes to cool this test chamber, which is on the order of a week. To test both “on-sky” conditions (with the blackbody above the detectors) and polarization properties and light spectra (with the blackbody out of the way) thus requires two lengthy cool-downs in two configurations. The goal of the second portion of my project is to design a system that allows both sets of tests to be performed in one cool-down. I will do so by creating a mechanical frame capable of holding and rotating the blackbody load away from the detectors. If there is time near the end of the project, this load will test detectors intended for South Pole Telescope 3g operations.