Progress on the 3x1x1 detector
Jennifer Toes, 20/10/2017
The inside of the ProtoDUNE, the next step after the 3x1x1 detector (Image: CERN)
Following the installation of the WA105 3x1x1 detector at CERN in 2016, the cryostat was filled with liquid argon (LAr) in early 2017 and began taking data in June.
Researchers involved in the AIDA-2020 project’s Work Package 8 (WP8) have been involved in the installation and commissioning of the detector, and continue to develop technology and analyse its test data.
The 3x1x1 detector (named for its dimensions in meters) is a prototype of Dual-Phase Liquid Argon Time Projection Chamber (DP LAr TPC) technology, which aims to demonstrate its feasibility for much larger experiments in the future. Researchers will be able to understand how well dual phase technology would scale up for use in the Deep Underground Neutrino Experiment (DUNE), which will make definitive measurements of neutrino properties.
As the name suggests, DP LAr TPC technology uses argon in both its liquid and gaseous state. Ionising particles, produced as the decay products of neutrinos) cross the liquid argon and produce electrons and light. The charge is then drifted upwards and the electrons are extracted into the gas region by means of an extraction grid.
Above the grid, circuit board-like large electron multipliers (LEMs), amplify the signal. LEMs contain many tiny holes, spaced a fraction of a millimetre apart. As the electrons move across the holes, they experience a very high electric field and produce secondary electrons, amplifying the charge signal. The latter combined with the light signal may be used to make a 3D reconstruction of the particles’ track.
Whilst previous prototypes have used three litres and 250 litres of liquid argon (active volume), the 3x1x1 prototype is the first to use 4.2 tonnes, which offers a significant increase up to ton scale experiments. Following this increase, the next step will jump to a 300 ton prototype called Dual-Phase ProtoDUNE, also to be built at CERN. As the 3x1x1 features many of the same technical challenges of the Dual-Phase ProtoDUNE, it serves as a test bench for the detector to come in 2018.
The installation of the WA105 cryostat (Image: Maximilien Brice/CERN)
Laura Molina Bueno (ETH Zurich), one of the Operation Coordinators of the WA105 experiment, details the motivation for the experiment: “The 3x1x1 prototype will open the path to future detectors by measuring the extraction of electron signals and their amplification at a scale never tested before. We couldn’t take for granted everything would work on a larger scale.”
As of October 2017, the WA105 Collaboration continues to take data from the detector and have begun simultaneous data analysis.
Laura Manenti (University College London), also an Operation Coordinator of the experiment, explains the future avenues open to the collaboration: “Many of the components of the 3x1x1 are similar to the Dual-Phase ProtoDUNE. So, it is very important to have a good feedback before moving to the future detector.”
Once the data has confirmed the reliability of the design and materials for large-scale neutrino studies, the 3x1x1 detector will be dismantled, and researchers will be entirely focussed on the commissioning of the Dual-Phase ProtoDUNE, which will bring them one-step closer to DUNE.