Simons Observatory: on-sky performance of radio-transparent multi-layer insulation using Styroace-II styrofoam.

Area of Science:

• Astrophysical instrumentation
• Cryogenic engineering
• Thermal management

Background:

• Bolometric detector arrays require extreme cooling (sub-100 mK) for sensitive measurements.
• Ambient thermal radiation poses a significant challenge to achieving and maintaining these low temperatures.
• Effective thermal shielding is crucial for the performance of cryogenic instruments.

Purpose of the Study:

• To evaluate the on-sky performance of a radio-transparent multi-layer insulation filter (RT-MLI).
• To quantify the rejection efficiency of ambient thermal radiation by the RT-MLI filter.
• To assess the thermal loading and millimeter-wave transmission characteristics of the filter.

Main Methods:

• Implementation of a novel RT-MLI filter utilizing Styroace-II styrofoam.
• Integration of the filter with a 0.42 m diameter aperture feeding a sub-100 mK bolometric detector array.
• Performance evaluation under operational (on-sky) conditions using a dilution refrigerator.

Main Results:

• The RT-MLI filter achieved greater than 90% rejection of expected incident infrared radiation.
• Measured transmitted power was less than 12 W, indicating high thermal insulation effectiveness.
• Transmitted power within the detector passbands was consistent with a lower bound of 95% rejection.

Conclusions:

• The RT-MLI filter demonstrates high performance in rejecting ambient thermal radiation for cryogenic detectors.
• The filter design and placement are effective in minimizing thermal loading.
• The RT-MLI is a viable solution for thermal shielding in sensitive millimeter-wave astronomical instruments.