The Simons Observatory: On-sky performance of radio-transparent multi-layer insulation (RT-MLI) using Styroace-II Styrofoam

TL;DR

This paper evaluates the on-sky performance of a radio-transparent multi-layer insulation filter made from Styroace-II styrofoam, demonstrating high IR radiation rejection and low transmitted power for bolometric detectors in a cryogenic observatory.

Contribution

It introduces and tests a novel RT-MLI filter using Styroace-II styrofoam, showing effective IR rejection and suitability for cryogenic radio astronomy applications.

Findings

>90% IR radiation rejection

<12 W transmitted power measured

>95% transmission in detector passbands

Abstract

We present the on-sky performance of a Radio-Transparent Multi-Layer Insulation filter (RT-MLI) that uses Styroace-II styrofoam to reject ambient thermal radiation from entering a 0.42 m diameter aperture to a sub-100 mK bolometric detector array cooled by a dilution-refrigerator. We find that greater than 90% of the expected incident infra-red (IR) radiation is rejected, resulting in $<$12 W of measured transmitted power. Transmitted power in the detector passbands is consistent with a lower bound of 95%. We address filter design and placement, thermal loading, and mm-wave transmission.