The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module

The Simons Observatory (SO) includes four telescopes that will measure the temperature and polarization of the cosmic microwave background using over 60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES bolometers are read out by a microwave RF SQUID multiplexing system with a multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to magnetic field pickup and that it is hard to predict how they will respond to such fields, it is important to characterize the magnetic response of these systems empirically. This information can then be used to limit spurious signals by informing magnetic shielding designs for the detectors and readout. This paper focuses on measurements of magnetic pickup with different magnetic shielding configurations for the SO universal multiplexing module (UMM), which contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic pickup of a prototype UMM was tested under three shielding configurations: no shielding (copper packaging), aluminum packaging for the UMM, and a tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold stage. We also present measurements of the pickup in the UMM when aluminum feedhorns are installed. The measurements show that the aluminum packaging outperforms the copper packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K shield further increases the relative shielding factor in the aluminum configuration by 1-2 orders of magnitude. The addition of feedhorns provides a factor of 30 improvement when the tin/lead shield is not installed and a factor of 5 improvement when it is.

This work was supported in part by a grant from the Simons Foundation (Award #457687, B.K.). ZBH acknowledges support from a NASA Space Technology Graduate Research Opportunities Award. SKC acknowledges support from NSF award AST-2001866. ZX is supported by the Gordon and Betty Moore Foundation through grant GBMF5215 to the Massachusetts Institute of Technology.

Authors and Affiliations

1. Department of Physics, Cornell University, Ithaca, NY, 14853, USA

   Zachary B. Huber, Yaqiong Li, Eve M. Vavagiakis, Steve K. Choi, Cody J. Duell, Ben Keller & Michael D. Niemack

2. Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, NY, 14853, USA

   Yaqiong Li & Michael D. Niemack

3. Department of Astronomy, Cornell University, Ithaca, NY, 14853, USA

   Steve K. Choi & Michael D. Niemack

4. Quantum Sensors Group, NIST, 325 Broadway, Boulder, CO, 80305, USA

   Jake Connors & Johannes Hubmayr

5. Department of Physics, University of Colorado Boulder, Boulder, Colorado, 80309, USA

   Jake Connors

6. NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA

   Nicholas F. Cothard

7. Department of Physics, University of California San Diego, La Jolla, CA, 92093, USA

   Nicholas Galitzki

8. Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ, 08544, USA

   Erin Healy, Heather McCarrick, Yuhan Wang & Kaiwen Zheng

9. Department of Astronomy, University of Virginia, Charlottesville, VA, 22904, USA

   Bradley R. Johnson

10. MIT Kavli Institute, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA, 02139, USA

    Zhilei Xu

Corresponding author

Correspondence to Zachary B. Huber.

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