With photon-noise dominated detectors, CMB experiments become more sensitive only by increasing detector count. Current experiments have on the order of 10,000 detectors, and future experiments propose 5-50x that figure. Reading out these large focal planes requires superconducting multiplexing technology. One concern with this technology is its potential to inject false signal into data via magnetic fields. We investigate magnetic field effects and potential shielding solutions within the context of readout electronics made for the South Pole Telescope's SPT-3G camera.

We explore two magnetic shielding technologies: high-μ metals and superconducting shielding. The high-μ shield is a box made of Amuneal A4K, an alloy designed for high permeability at cryogenic temperatures. The box geometry is a half cylinder to allow for simultaneous testing of shielded and unshielded readout electronics. The superconducting shielding is a NbN-coated cover installed around a superconducting filter network. We saw no attenuation of coupling to the applied external field with the A4K box, and the NbN shield amplifies this coupling in its current implementation. We found the A4K box is effective at isolating some coupling to magnetic fields inherent to the readout electronics. Further testing is needed to differentiate neighboring-SQUID effects from other intermodule coupling before evaluating the NbN shield's crosstalk isolation capability.

Date Published: 9 July 2018
PDF: 9 pages
Proc. SPIE 10708, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, 1070846 (9 July 2018); doi: 10.1117/12.2314188

Published in SPIE Proceedings Vol. 10708:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX
Jonas Zmuidzinas; Jian-Rong Gao, Editor(s)