The Simons Observatory: Improved Cryogenic Struts for use in the Large Aperture Telescope Receiver

TL;DR

This paper presents a novel glue joint design for cryogenic struts in the Simons Observatory's Large Aperture Telescope Receiver, enhancing strength and durability for maintaining detector temperatures.

Contribution

The paper introduces a new glue joint profile with increased strength and safety margin, proven through design, simulation, and three years of operational testing.

Findings

Cohesive failure mode with 10% higher yield strength

Ultimate strength increased by 33% over smooth-walled design

Struts have endured thermal cycles for three years without damage

Abstract

The Simons Observatory Large Aperture Telescope Receiver (SO LATR) is a next generation Cosmic Microwave Background camera equipped with > 60, 000 detectors operating at 100 mK. Maintaining these detectors at the correct temperatures and locations requires stiff, cryogenically insulating struts. In this paper we report the design and performance of a novel glue joint in a strut used in the SO LATR to achieve the required performance. We use a tapped hole and set screw to create a profile on the exterior and interior wall of the glue joint, respectively, which greatly increases the strength of that joint by changing the failure mode from adhesive to cohesive. The failure mode of the resulting glue joint is cohesive with a yield strength 10% higher than a comparable smooth-walled design, and an ultimate strength 33% higher. Comparisons of the measured yield strength to the predicted axial load on the strut from simulations results in a factor of safety for the strut of 7. These struts have been installed in the SO LATR for three years and have undergone numerous thermal cycles from 300 K to 100 mK with no evidence of damage to the glue joint.