A method of generating a pressurized, sub-cooled mixed-phase cryogen is disclosed, including providing a cryogenic system including a reservoir containing a liquid cryogen; and a heat exchange coil immersed in the liquid cryogen, the heat exchange coil having an input end and an output end not immersed in the liquid cryogen; introducing a pressurized gas cryogen to the input end of the heat exchange coil; cooling the pressurized gas cryogen within the heat exchange coil; and collecting the pressurized gas cryogen at an output end of the heat exchange coil.