  The MUSCAT instrument is a large-format camera planned for installation on
the Large Millimeter Telescope (LMT) in 2018. MUSCAT requires continuous
cooling of several large-volume stages to sub-Kelvin temperatures, with the
focal plane cooled to 100 mK. Through the use of continuous sorption coolers
and a miniature dilution refrigerator, the MUSCAT project can fulfil its
cryogenic requirements at a fraction of the cost and space required for
conventional dilution systems. Our design is a helium-light system, using a
total of only 9 litres of helium-3 across several continuous cooling systems,
cooling from 4 K to 100 mK. Here we describe the operation of both the
continuous sorption and the miniature dilution refrigerator systems used in
this system, along with the overall thermal design and budgeting of MUSCAT.
MUSCAT will represent the first deployment of these new technologies in a
science-grade instrument and will prove the concept as a viable option for
future large-scale experiments such as CMB-S4.
