Resonant cryogenic chopper

We describe the design, construction, and performance of a resonant cryogenic chopper that operates at 4.2 K. The chopper is mechanically and thermally robust; it can occult a 2.54-cm aperture at 4.5 Hz while dissipating approximately 1 mW. Both the stator and rotor magnetic fields are controllable to allow for performance optimization and to help in measuring any possible interference effects. Data on long-term amplitude stability are presented.