The Atacama Cosmology Telescope: The polarization-sensitive ACTPol instrument

TL;DR

The paper introduces ACTPol, an upgraded polarization-sensitive receiver for the Atacama Cosmology Telescope, designed to enhance measurements of CMB anisotropies, polarization, and related cosmological signals with high sensitivity and resolution.

Contribution

It presents the design, implementation, and initial performance of ACTPol, a new instrument with polarization-sensitive detectors and multi-frequency arrays for advanced CMB observations.

Findings

Successfully commissioned and operated the first full season of ACTPol.

Achieved high sensitivity and resolution in polarization measurements.

Demonstrated capability to measure CMB anisotropies and related signals.

Abstract

The Atacama Cosmology Telescope (ACT) is designed to make high angular resolution measurements of anisotropies in the Cosmic Microwave Background (CMB) at millimeter wavelengths. We describe ACTPol, an upgraded receiver for ACT, which uses feedhorn-coupled, polarization-sensitive detector arrays, a 3 degree field of view, 100 mK cryogenics with continuous cooling, and meta material anti-reflection coatings. ACTPol comprises three arrays with separate cryogenic optics: two arrays at a central frequency of 148 GHz and one array operating simultaneously at both 97 GHz and 148 GHz. The combined instrument sensitivity, angular resolution, and sky coverage are optimized for measuring angular power spectra, clusters via the thermal Sunyaev-Zel'dovich and kinetic Sunyaev-Zel'dovich signals, and CMB lensing due to large scale structure. The receiver was commissioned with its first 148 GHz array in 2013, observed with both 148 GHz arrays in 2014, and has recently completed its first full season of operations with the full suite of three arrays. This paper provides an overview of the design and initial performance of the receiver and related systems.