The Largest Liquid Argon Neutrino Detector in the World: ProtoDUNE

Title: “ProtoDUNE and a Dual-Phase LArTPC

Author: Andrea Scarpelli on behalf of the DUNE Collaboration

Reference: arXiv:1902.04780

ProtoDUNE is helping lead the way for the next generation of long-baseline neutrino experiments, and is exceeding expectations.

DUNE, the Deep Underground Neutrino Experiment, will deploy four massive Liquid Argon Time Projection Chambers (LArTPCs) totaling 40 kilotons of liquid argon to study neutrinos, one of the universe’s most elusive particles. Time Projection Chambers use sensitive volumes of gas or liquid exposed to electric and magnetic fields to reconstruct 3D particle trajectories and interactions. Liquid argon is advantageous for several reasons. It’s relatively inexpensive, produces light when energetic charged particles pass by (scintillates), and won’t absorb electrons produced by ionizing radiation before they reach the detector arrays (since it’s a noble element). It is also very dense, increasing the chances of a particle interacting in the detectors compared to other materials.

The 1100 scientists involved with DUNE plan to use two detectors and the world’s most intense neutrino beam. A smaller detector, located at the Fermi National Accelerator Laboratory in Batavia, Illinois, will record particle interactions near the neutrino beam source. The largest detector, buried more than a kilometer underground, will be located at the Sanford Underground Research Laboratory in Lead, South Dakota. This is 1,300 kilometers away from the neutrino source, known as the “baseline” of the long-baseline neutrino experiments. This distance allows the neutrinos time to oscillate, or change their flavor as they travel, before being detected in the large LArTPC. Scientists can then learn more about neutrinos by using the physics of neutrino oscillation. DUNE aims to measure the neutrino oscillation parameters, determine the neutrino mass hierarchy and search for CP violation in the leptonic sector of the Standard Model.

DUNE will consist of two detectors: one located at Fermilab in Batavia, IL, and one 1,300 km downstream of the neutrino beam source, at the Sanford Underground Research Laboratory in Lead, South Dakota. Source:

Before DUNE can get started, characterizing the detector response and proving the feasibility of the DUNE technology at the kiloton scale is crucial. That’s where ProtoDUNE comes in.

In LArTPCs, 3D images of particle events are formed by collecting electrons produced during Argon ionization and drifting them onto detectors using an applied field. The most common setup for these detectors is a Single-Phase (SP) LArTPC, where electrons are drifted horizontally onto a readout. However, because in this setup the drift length cannot exceed 3-4 meters, using this technology for DUNE requires a complicated design with several TPCs within the volume of argon. An alternative approach is a Dual-Phase (DP) setup, where the electrons are drifted vertically and amplified by a strong field applied inside a thin layer of argon gas just before the readout. This amplification is used to compensate for electron losses or noise caused by the larger drift length differences.

Left: Model of ProtoDUNE-SP (Single-Phase). Right: Model of ProtoDUNE-DP (Dual-Phase). Source: arXiv:1902.04780

The ProtoDUNE experiment, located at CERN, is designed to test both the SP and DP setups for the DUNE far detector. Using a total Ar mass of 0.7 kilotons, ProtoDUNE will also test the detector response and calibration with both a charged particle beam and using cosmic rays. Testing the designs of the DUNE components at a 1:1 scale wherever possible will demonstrate the technology and allow DUNE to move forward.

Scientists inside of ProtoDUNE-DP’s field cage, which use high voltages to drift particles towards the readouts using an electric field. Source: Symmetry magazine

In the fall of 2018, ProtoDUNE came alive, and measured neater tracks with less noise from electronics than had been expected. While DUNE will be much larger, this first prototype detector, ProtoDUNE-SP, is now the largest LArTPC ever to be constructed, and to have it functioning well is a key step towards realizing DUNE. However, there is certainly a lot more work to do before DUNE’s two detectors come alive in 2026. Stay tuned!


Further Reading:

  1. DUNE website:
  2. “Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 1: The LBNF and DUNE Projects”:
  3. “Understanding the energy resolution of liquid argon neutrino detectors”: