Transient heat transfer in helium II due to a sudden vacuum break

To ensure future cryogenic devices meet safety and operational specifications, significant value is gained from a developed understanding of the transient heat fluxes that result from failure of an insulating vacuum jacket around a helium II (He II)-cooled device. A novel, one-dimensional experiment is successfully performed examining the phenomena immediately following a vacuum rupture onto a cryosurface. In the experiment, a fast-opening (∼10 ms) valve isolates a rigid container of ultra high purity nitrogen (⁠$N2$⁠) gas kept at room temperature and adjustable pressure from a vertically oriented, highly evacuated (∼10⁻³ Pa) tube roughly 1 m in length. The bottom of the evacuated tube is sealed via a 2.54 mm thick copper disk, whose bottom surface is in intimate contact with an open column of He II (∼1.8 K). The evacuated tube, disk, and He II column share a diameter of 24 mm. Opening the valve results in a vacuum rupture. $N2$ gas is immediately drawn into the evacuated space and cryopumped onto the disk as a growing layer of solid cryodeposit. Various coupled transient heat transfer processes proceed as the internal energy of the warm gas is transferred through the growing layer of solid $N2$⁠, through the copper disk, and into the He II column. This work examines the qualitative nature of these transient phenomena and the magnitude of the heat fluxes present through each of the series of thermal resistances.