6. A process for optimizing the capacity of a cryogenic refrigerator within a given temperature range that includes the steps of: providing a regenerator which is operatively associated with a single-stage cold head: creating adjacent layers of different material within said regenerator so that a working fluid flows in series through the layers from a warm side of the regenerator toward a cold side of the regenerator; and selecting the material in each adjacent layer to provide the refrigerator with an optimum capacity between 15 K and 80 K providing a first layer of about 200 mesh copper-bronze material adjacent the warm side of the regenerator, a second layer of about 120 mesh copper-bronze material adjacent the first layer, and a third layer of lead spheres adjacent the second layer and sizing the length of the third layer so that it is about one half of the length of the first and second layers.
6. A process for optimizing the capacity of a cryogenic refrigerator within a given temperature range that includes the steps of: providing a regenerator which is operatively associated with a single-stage cold head: creating adjacent layers of different material within said regenerator so that a working fluid flows in series through the layers from a warm side of the regenerator toward a cold side of the regenerator; and selecting the material in each adjacent layer to provide the refrigerator with an optimum capacity between 15 K and 80 K providing a first layer of about 200 mesh copper-bronze material adjacent the warm side of the regenerator, a second layer of about 120 mesh copper-bronze material adjacent the first layer, and a third layer of lead spheres adjacent the second layer and sizing the length of the third layer so that it is about one half of the length of the first and second layers. 14. The process of claim 6 that includes the further step of providing a cryogenic pump having a pumping surface, cooling the pumping surface with said cold head, and selecting the regenerator layer material to optimize the cold head temperature within the desired temperature range of the pumping surface.