There is a better article on the subject here [0] - it's indeed a long tube with lots of temperature sensors (48) to measure temperatures at different depths in

There is a better article on the subject here [0] - it's indeed a long tube with lots of temperature sensors (48) to measure temperatures at different depths in the liquid argon volume. The data can be used to check whether the cooling and filtration system is working correctly and correlate that with contamination of the liquid argon by other material (e.g. outgassing from building material). These detectors aren't described (but mentioned) in the original DUNE design report [1], but it's an extremely interesting 'read' if you want to get a feel for which parts work together in the detectors. [0] https://phys.org/news/2018-08-temperature-protodune.html https://phys.org/news/2018-08-temperature-protodune.html [1] https://arxiv.org/abs/1601.02984 https://arxiv.org/abs/1601.02984