Modern linear particle accelerators (LINAC) for high energy physics research use superconducting radio frequency (SRF) technology with liquid helium (LHe) cooling. The SRF beam-line or the ‘cavity string’ of such a LINAC is essentially a long high vacuum channel immersed in LHe with interconnects near the atmosphere. Accidental loss of the beam-line vacuum to the atmosphere, say due to a rupture, is perceived to be catastrophic as the rupture will expose the LHe enclosed vacuum space to the warm atmospheric air. The air rapidly flowing in from the local rupture will propagate down the vacuum space, and on condensation on the cold beam-line, will transfer large heat fluxes to the LHe. Our research on this subject has mainly focused on understanding how in the presence of condensation, the in-flowing air will propagate down the vacuum space. The scenario is studied by venting near-atmospheric nitrogen gas (a substitute for air) to a vacuum tube immersed in a LHe bath and then measuring the gas front propagation speed along the vacuum tube.
So far we have experimented with and have characterized the gas propagation in a straight long 1.5 inch outer diameter tube, 1.5 meter long and immersed in 4.2 K liquid helium. Future activities include development of apparatus and detailed parametric experiments with 2 K superfluid helium (He II) coolant.
- Sudden Loss of Vacuum apparatus Sudden Loss of Vacuum apparatus
- Sudden loss of vacuum schematic Sudden loss of vacuum schematic