A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument

Sean Bryan , Peter Ade , Mandana Amiri , Steven Benton , Richard Bihary , James Bock , J. Richard Bond , H. Cynthia Chiang

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Carlo Contaldi Brendan Crill Olivier Dore Benjamin Elder Jeffrey Filippini Aurelien Fraisse Anne Gambrel Natalie Gandilo Jon Gudmundsson Matthew Hasselfield Mark Halpern Gene Hilton Warren Holmes Viktor Hristov Kent Irwin William Jones Zigmund Kermish Craig Lawrie Carrie MacTavish Peter Mason Krikor Megerian Lorenzo Moncelsi Thomas Montroy Tracy Morford Johanna Nagy C. Barth Netterfield Ivan Padilla Alexandra S. Rahlin Carl Reintsema Daniel C. Riley John Ruhl Marcus Runyan Benjamin Saliwanchik Jamil Shariff Juan Soler Amy Trangsrud Carole Tucker Rebecca Tucker Anthony Turner Shyang Wen Donald Wiebe Edward Young

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classification 🌌 astro-ph.IM astro-ph.CO

keywords cryogenicflightrotationspiderallowsapertureclearduring

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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 degrees. The system performed well in Spider during its successful 16 day flight.

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A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument

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