In 1955 C.R. Meissner revealed his in-chamber water vapor pumping concept, based on the early work of Dewar. Meissner employed both boiling liquid and heated gaseous nitrogen to rapidly temperature cycle a coil of tubing between cryogenic and above-ambient temperatures. Several vacuum system manufacturers incorporated advanced versions of the nitrogen cooled and heated "Meissner Coil" in their apparatus starting in the late 1960s. Although effective, it proved wasteful of nitrogen and difficult to control. Early closed loop mechanical refrigeration systems had reliability and low temperature limitations and were not widely used. Also they used a flammable refrigerant in the lower stage of a two-compressor cascade cycle. This was not always acceptable. In the mid-1980s a reliable single-compressor auto-refrigerating cascade (ARC) system with fast cycling capabilities between high and cryogenic low temperatures was developed. Its water vapor cryopumping proved more economical and operated with far lower power inputs than previous pumping methods. A mixture of Freons and an inert gas (argon or nitrogen) served as the refrigerant. The Freons were replaced in the 1990s by environmentally benign materials. Rapid temperature cycling of a cryopumping surface mounted directly within the vacuum space has proven its merits because of its high speed, reliability and energy efficiency.