MARCO (Multi-purpose Apparatus for Research on CO2 cooling) is a CO2 cooling unit based on the 2PACL concept (developed for the LHCb-Velo CO2 cooling system).

The capacity of MARCO is in the order of 1kW and the operational temperature range is from room temperature down to -40°C.

MARCO is designed to support CO2 cooling development in general. It has been designed and built in 2012 in collaboration between MPI (Germany), NIKHEF (Netherlands) and CERN. The commissioning was done at CERN by PH/DT during winter 2012/2013 and since summer 2013, MARCO is running at DESY (Germany) on a test beam setup. It will come back to CERN around summer 2014 and will be used as a test setup for detector CO2 cooling developments.

The design of MARCO served as a base for future CO2 cooling plants for experiments. The CO2 cooling for Atlas-IBL and KEKb-Belle 2 is directly derived from the MARCO design. The common design approach is named IBBeLle cooling plant as both IBL and Belle-2 have the same cooling requirements.