title: A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument.
abstract: We describe the cryogenic half-wave plate rotation mechanisms built for and used in Spider, a polarization-sensitive balloon-borne telescope array that observed the cosmic microwave background at 95 GHz and 150 GHz during a stratospheric balloon flight from Antarctica in January 2015. The mechanisms operate at liquid helium temperature in flight. A three-point contact design keeps the mechanical bearings relatively small but allows for a large (305 mm) diameter clear aperture. A worm gear driven by a cryogenic stepper motor allows for precise positioning and prevents undesired rotation when the motors are depowered. A custom-built optical encoder system monitors the bearing angle to an absolute accuracy of ±0.1(∘). The system performed well in Spider during its successful 16 day flight.
authors.affiliation: School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, USA.
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authors.affiliation: Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Department of Physics and CERCA, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
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authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
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authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
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authors.affiliation: Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia V6T 1Z1, Canada.
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authors.affiliation: Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, California 91125, USA.
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authors.affiliation: Department of Physics and CERCA, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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authors.affiliation: Department of Physics and CERCA, Case Western Reserve University, Cleveland, Ohio 44106, USA.
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