An improved method of supplying pressurized cold gas consistently of predominately N2 and He at low flow rate (typically under 1 g/s) with a desired N2 liquid fraction to an instrument requiring such is disclosed. Pressurized ultra-dry nitrogen gas of a controlled mass-flow rate is cooled inside fine coils bathed in liquid nitrogen to condense it to a vapor fraction less than about 20% and typically under 3%. A second gas stream consisting of predominately nitrogen plus helium, supplied from a controlled pressure, is cooled in a separate set of coils to an exit mean temperature significantly above the temperature of saturated nitrogen vapor in this mixture. The fluid from the first (condensed) mixture is injected into the cooled gas from the second mixture and transferred through a thermally insulated line to the input of the instrument needing a supply of cold gas of a target vapor fraction.