Development of a cold chopper for TAO/MIMIZUKU: onboard test on MIMIZUKU

MIMIZUKU, the mid-infrared instrument for the 6.5-m telescope at the University of Tokyo Atacama Observatory (TAO), employs a cold chopper to perform chopping, which tilts the mirror placed at a temperature of about 20 K. The mirror rotates around two orthogonal axes, and its tilt angle is controlled by the balance between the restoring force of the flexural pivots and the magnetic force driven by the coils in the system. In this study, we developed a final-product model of the chopper and tested its on-board performance in MIMIZUKU. This experiment showed that the mirror could be operated with a stability of 3.34 × 10-4 and 3.24 × 10-4 degrees, and a transition time of 31.5 and 31.2 milliseconds for each rotation, when both rotations were driven at 5 Hz with an amplitude of 0.58 degrees, satisfying the performance requirements.