Repairing the vacuum system with pure nitrogen
On October 22 and 23, 2019, the GEO600 team together with a vacuum welding company closed the leak in the GEO600 north arm. After it had occured on August 1, 2017, when it was closed temporarily with vacuum glue. Another application of glue was need in mid December 2018. Now, the north arm was sealed off from the rest of the detector and filled with high-purity dry nitrogen. This allowed welding the leak and closing it permanently.
Read more about how the GEO600 team effort lead to a smooth repair operation and a running detector soon after in the LIGO Magazine.