Commissioning of the LEGEND experiment
at the Gran Sasso Laboratory

Despite objective difficulties, DLNP JINR scientists took a decisive part in the installation of the first 60 kg of detectors of enriched Ge-76 in the LEGEND setup located at the Gran Sasso National Laboratory (Italy). In addition to the direct assembling of detector strings, our specialists fabricated high-purity nylon mini-shrouds used to reduce the radioactive background of the experiment and for the first time performed the installation of the complete liquid argon instrumentation, developed and created by a joint team of scientists from JINR and the Technical University of Munich.

After a rather long preparatory phase, the LEGEND experiment moved on to the final stage - the installation of the first batch of detectors and a liquid argon instrumentation. The collaboration decided first to assemble 4 of 12 planned strings of detectors (the total mass of Ge-76 is about 60 kg) in order to test all components of the experimental setup. Note that final materials were used during the installation. This will allow, after collecting data for several months, assessing the real background level. It should also be emphasized that even now the mass of detectors exceeds the total mass of detectors in the predecessor GERDA experiment by more than 50%. At the end of this stage, we plan to assemble all available detectors.
 

To ensure an ultra-low background level of the setup, we had to make special nylon mini-shrouds which would surround the detector strings. The design of the mini-shrouds and their production are among areas of responsibility of the JINR group in LEGEND. Initially, we planned to manufacture all mini-shrouds in the clean room at JINR and then send them to Gran Sasso in special hermetic containers also developed by us. However, at present, the delivery of such containers to Gran Sasso has become practically impossible. In this regard, we decided to create all the mini-shrouds needed for the experiment in the clean room at the Technical University of Munich, with which we have long-term beneficial cooperation within the LEGEND and MONUMENT projects. Then we would deliver them to Italy and install in the setup. Everything planned was successfully completed in May 2022 during our business trip to Germany/Italy.

In parallel with the mini-shroud production, the second group of scientists from Dubna carried out an experimental work at Gran Sasso. They mounted and bonded germanium detectors in special low-background holders, and also performed a test assembly of two detector strings.

During the last week of our stay, 60 kg of germanium detectors were successfully assembled into 4 strings with our direct participation. We put on them the nylon mini-shrouds brought from Munich and installed the liquid argon instrumentation. Now it is time to collect the first experimental data, and then, in the fall of 2022, we plan to return to Gran Sasso to complete the installation of all available detectors and launch the full-scale LEGEND experiment.

Konstantin Gusev, Alexey Lubashevskiy, Nadezda Rumyantseva,
Egor Shevchik, Daniya Zinatulina,
photo by Enrico Sacchetti, Brady Bos