Cryogenic refrigeration apparatus

A system for producing a cold environment comprising fluid compression means for supplying fluid under pressure;

• a plurality of successive operating stages having variable displacement volumes;
• volume-changing means for varying the volumes of said displacement volumes;
• input channel means for permitting flow of fluid to and from said successive displacement volumes;
• first means for permitting input fluid to be introduced under pressure from said fluid compression means into said input channel means for flow therein to said successive displacement volumes;
• second means for permitting fluid in said input channel means to flow to said fluid compression means;
• third means for permitting fluid at reduced pressure to flow from the final one of said displacement volumes into an output channel means, said output channel means permitting flow of output fluid to said fluid compression means;
• whereby input fluid flowing from said fluid compression means under pressure in said input channel means to said first set of displacement volumes is pre-cooled by regenerative heat exchange with a portion of the structure of said input channel and by counterflow heat exchange with fluid flowing in said output channel means, and input fluid flowing in said input channel means to said final one of said displacement volumes is pre-cooled primarily by counterflow heat exchange with fluid flowing in said output channel;
• and
• means for thermally decoupling the volume changing means of at least one of said successive operating stages from said input and said output channel means.