A cryogenic rotation stage with a large clear aperture for the half-wave plates in the Spider instrument
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.
Review of Scientific Instruments
- Pub Date:
- January 2016
- Astrophysics - Instrumentation and Methods for Astrophysics;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- 11 pages, 7 figures, Published in Review of Scientific Instruments. v2 includes reviewer changes and longer literature review