Achieving 100mK: the Cyrogenic Systems of TolTEC

TolTEC is a next generation millimeter camera for the Large Millimeter Telescope (LMT). It utilizes Lumped Element Kinetic Inductance Detectors (LEKIDs) operated at cryogenic temperatures of approximately 100 mK. TolTEC has three arrays of LEKIDs at wavelengths of 1.1 mm, 1.4 mm and 2.0 mm, each featuring a few thousand detectors. TolTEC's focal planes and optics bench require a unique large-scale cryostat with multiple nested temperature stages. To cool the system, we rely on two cryogenic systems; an Auxiliary Pulse Tube Cooler which extracts the heat at the 45K and 4K stages, and a Dilution Refrigerator which extracts the heat at the 1K and 100 mK stages. Here we describe the design, modeling and characterization of each stage including both the thermal and mechanical challenges of working with meter-scale cryostats. We are currently transitioning from the design phase to assembly and testing and expect TolTEC to be commissioned at the LMT between Spring to Summer 2019.