Characterization of transition edge sensors for the Millimeter Bolometer Array Camera on the Atacama Cosmology Telescope.

The Atacama Cosmology Telescope (ACT) aims to measure the Cosmic Microwave Background (CMB) temperature anisotropies on arcminute scales. The primary receiver for ACT is the Millimeter Bolometer Array Camera (MBAC). The MBAC is comprised of three 32×32 transition edge sensor (TES) bolometer arrays, each observing the sky with an independent set of band-defining filters. The MBAC arrays will be the largest pop-up detector arrays fielded, and among the largest TES arrays built. Prior to its assembly into an array and installation into the MBAC, a column of 32 bolometers is tested at ~ 0.4 K in a quick-turn-around dip probe. In this paper we describe the properties of the ACT bolometers as revealed by data from those tests, emphasizing a characterization that accounts for both the complex impedance and the noise as a function of frequency.