The Simons Observatory: Magnetic Sensitivity Measurements of Microwave SQUID Multiplexers

Abstract

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field $\sim$70,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities. The SO Universal Focal Plane Modules (UFMs) each contain a 150 mm diameter TES detector array, horn or lenslet optical coupling, cold readout components, and magnetic shielding. SO will use a microwave SQUID multiplexing ($\mu$MUX) readout at an initial multiplexing factor of $\sim$1000; the cold (100 mK) readout components are packaged in a $\mu$MUX readout module, which is part of the UFM, and can also be characterized independently. The 100 mK stage TES bolometer arrays and microwave SQUIDs are sensitive to magnetic fields, and their measured response will vary with the degree to which they are magnetically shielded. We present measurements of the magnetic pickup of test microwave SQUID multiplexers as a study of various shielding configurations for the Simons Observatory. We discuss how these measurements motivated the material choice and design of the UFM magnetic shielding.

arXiv comment5 pages, 6 figures, conference proceedings submitted to IEEE Transactions on Applied Superconductivity

References in corpus (8)

• Optical Design of the Atacama Cosmology Telescope and the Millimeter Bolometric Array Camera
• Longitudinal Proximity Effects in Superconducting Transition-Edge Sensors
• The Cosmology Large Angular Scale Surveyor
• Microwave SQUID Multiplexer demonstration for Cosmic Microwave Background Imagers
• The bolometric focal plane array of the Polarbear CMB experiment
• Simons Observatory Microwave SQUID Multiplexing Readout -- Cryogenic RF Amplifier and Coaxial Chain Design
• Magnetic Sensitivity of AlMn TESes and Shielding Considerations for Next-Generation CMB Surveys
• Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors

Cited by in corpus (4)

• Mitigation of the Magnetic Field Susceptibility of Transition Edge Sensors using a Superconducting Groundplane
• Assembly development for the Simons Observatory focal plane readout module
• Demonstration of a 1820 channel multiplexer for transition-edge sensor bolometers
• The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module