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

• Published in: Review of Scientific Instruments
• Main Authors: Bryan, Sean, Ade, Peter, Amiri, Mandana, Benton, Steven, Bihary, Richard, Bock, James, Bond, J. Richard, Chiang, H. Cynthia, Contaldi, Carlo, Crill, Brendan, Dore, Olivier, Elder, Benjamin, Filippini, Jeffrey, Fraisse, Aurelien, Gambrel, Anne, Gandilo, Natalie, Gudmundsson, Jon, Hasselfield, Matthew, Halpern, Mark, Hilton, Gene, Holmes, Warren, Hristov, Viktor, Irwin, Kent, Jones, William, Kermish, Zigmund, Lawrie, Craig, MacTavish, Carrie, Mason, Peter, Megerian, Krikor, Moncelsi, Lorenzo, Montroy, Thomas, Morford, Tracy, Nagy, Johanna, Netterfield, C. Barth, Padilla, Ivan, Rahlin, Alexandra S., Reintsema, Carl, Riley, Daniel C., Ruhl, John, Runyan, Marcus, Saliwanchik, Benjamin, Shariff, Jamil, Soler, Juan, Trangsrud, Amy, Tucker, Carole, Tucker, Rebecca, Turner, Anthony, Wen, Shyang, Wiebe, Donald, Young, Edward
• Other Authors: National Science Foundation, National Aeronautics and Space Administration
• Format: Article in Journal/Newspaper
• Language: English
• Published: AIP Publishing 2016
• Subjects: Instrumentation; Antarc*; Antarctica
• Online Access: http://dx.doi.org/10.1063/1.4939435; https://pubs.aip.org/aip/rsi/article-pdf/doi/10.1063/1.4939435/13910245/014501_1_online.pdf

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.