ProtoDUNE

The photovoltaic sensors and APAs inside the ProtoDUNE-VD.

The ProtoDUNE experiment is a prototype for DUNE in development by CERN, which will measure neutrino collisions. DUNE will use a liquid-argon time projection chamber to detect neutrinos, also known as a LArTPC. Neutrino collisions knock electrons off of atoms and release light energy, both of which can be measured by ProtoDUNE. Scientists use a negatively-charged anode plane array (APA) to attract and record the path of the electrons, thereby recording information about the collision itself. The ProtoDUNE detector is around the size of a three-story house, and the DUNE project will use modules twenty times the size of ProtoDUNE. ProtoDUNE was successfully tested in 2018; as of 2023 it is the largest LArTPC ever constructed. Two detectors have been built at the neutrino platform, each containing around 800 metric tons of liquid argon. A cryostat is used to insulate the detector, which needs to be kept at temperatures of -184°C (-300°F) for the argon to remain liquid.

Construction

It took two years to build the first ProtoDUNE detector, and another eight weeks to fill it with 800 tons of liquid argon. Originally, one detector was built to be single-phase (ProtoDUNE-SP), using only liquid argon, while the other was built to be dual-phase (ProtoDUNE-DP), using both liquid and gaseous argon. The goal of the prototypes is to solve any engineering problems that DUNE might face before construction begins. A group led by Bob Paulos in the University of Wisconsin–Madison Physical Sciences Lab designed the APA for the single-phase detector, and the APAs were built by the UW–Madison group and the Science and Technology Facilities Council’s Daresbury Laboratory. In addition, CERN designed a cathode plane that would repel electrons. The dual-phase detector operated similarly, but with a slightly different array configuration. Although DUNE's neutrinos will be provided by the Long-Baseline Neutrino Facility, CERN expanded their existing network to use a particle beam to test the detectors. The beam window system that allowed researchers to test ProtoDUNE was designed, fabricated, and installed by the Department of Energy's Lawrence Berkeley National Laboratory.

Testing

In 2018, ProtoDUNE recorded its first particle tracks. In 2020, researchers published a paper regarding the testing of the ProtoDUNE-SP detector. They used an 800-GeV beam of protons and electrons from CERN's SPS accelerator to test the capabilities of the ProtoDUNE-SP detector. In the test, the results from ProtoDUNE-SP were cross-checked with those from particle detectors located just before the detector. ProtoDUNE uses reconstruction software to differentiate an actual interaction from noise. This test revealed that the detector had a signal-to-noise ratio of fifty to one and that over 99% of the detector channels were working properly. As of 2023, CERN is building ProtoDUNE II, which will include a vertical drift detector (ProtoDUNE-VD). ProtoDUNE II will contain four APAs and light sensors.