The system operates basically as follows; two-phase flow of LN2 enters the phase separator. The gas is vented to atmosphere outside the lab leaving a volume of pure, gas-free LN2 at –320° F. The liquid is gravity fed to the cryoshroud though a triaxial feed line. The LN2 is slightly sub-cooled at the lower end of the piping due to the hydrostatic head of liquid. As the liquid enters the cryoshroud and picks up heat, the density changes, and the lighter LN2 is returned to above the liquid level in the phase separator. Gas is vented off, and the liquid is re-used.