The design and testing of a liquid helium cooled tube system for simulating sudden vacuum loss in particle accelerators

摘要

Loss of vacuum in particle accelerators and other cryogenic systems can lead to substantial equipment damage and possible personnel injuries. Systematic laboratory studies of the relevant heat and mass transfer processes are strongly desired to help mitigate these concerns. In our early experiments on sudden vacuum break in a liquid helium cooled tube, an exponential slowing down of the propagating condensing gas was observed. This slowing down appeared to be much stronger in the experiments with superfluid helium (He II) than with normal helium (He I). However, further analysis suggested that this apparent stronger slowing down in the He II experiment was likely caused by the gas condensation in the cold section of the tube above the liquid helium bath. In this paper, we discuss modifications to our vacuum tube system to control the starting point of gas condensation. System improvements included vacuum insulation, multi-layer insulation, heating and additional sensors. Testing of the improved system reveals that the starting point of the gas condensation can be well controlled in both He I and He II experiments. The slightly stronger slowing effect in He II observed with the new tube system can now be more affirmatively attributed to the heat transfer difference between He I (i.e., convection) and He II (i.e., thermal counterflow).