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TolTEC is an upcoming millimeter-wave imaging polarimeter designed to fill the focal plane of the 50-m-diameter Large Millimeter Telescope (LMT). Combined with the LMT, TolTEC will offer high-angular-resolution (5–10 ) simultaneous, polarization-sensitive observations in three wavelength bands: 1.1, 1.4, and 2.0 mm. Additionally, TolTEC will feature mapping speeds greater than 2 deg2∕mJy2∕h , thus enabling wider surveys of large-scale structure, galaxy evolution, and star formation. These improvements are only possible through the integration of approximately 7000 low-noise, high-responsivity superconducting Lumped Element Kinetic Inductance Detectors. Utilizing three focal planes of detector arrays requires the design, fabrication, and characterization of a unique, large-scale cryogenic system. Based on thermal models and expected photon loading, the focal planes must have a base operational temperature below 150 mK. To achieve this base temperature, TolTEC utilizes two cryocoolers, a Cryomech pulse tube cooler and an Oxford Instruments dilution refrigerator, to establish four thermal stages: 45 K, 4 K, 1 K, and 100 mK. During the design phase, we developed an object-oriented Python code to model the heat loading on each stage as well as the thermal gradients throughout the system. This model has allowed us to improve thermal gradients in the system as well as locate areas of poor thermal conductivity prior to ending a cooldown. The results of our model versus measurements from our cooldowns will be presented along with a detailed overview of TolTEC’s cryogenic system. We anticipate TolTEC to be commissioned at the LMT by Spring 2020. 

The design and characterization of a low noise amplifier optimized for the readout of microwave kinetic inductance detectors is described. The work is first motivated through a description of microwave kinetic inductance detectors and a discussion of the requirements for the low-noise amplifiers employed for readout of these devices. Next, the design of a two-stage silicon germanium cryogenic integrated circuit low noise amplifier is presented. The small-signal and large-signal characteristics of the fabricated amplifier are then measured. It is shown that, at a physical temperature of 16 K, the amplifier achieves a gain of greater than 30 dB and an average noise temperature of 3.3 K over the 0.4–1.2 GHz frequency band while dissipating less than 7 mW. Moreover, the wideband compression characteristics are measured it is found that the linearity of the amplifier is sufficient to support frequency domain multiplexed readout of more than 500 detectors. 

TolTEC is a new camera being built for the 50-meter Large Millimeter-wave Telescope (LMT) in Puebla, Mexico to survey distant galaxies and star-forming regions in the Milky Way. The optical design simultaneously couples the field of view onto focal planes at 150, 220, and 280 GHz. The optical design and detector properties, as well as a data-driven model of the atmospheric emission of the LMT site, inform the sensitivity model of the integrated instrument. This model is used to optimize the instrument design, and to calculate the mapping speed as an early forecast of the science reach of the instrument.