The Deep Underground Neutrino Experiment (DUNE) is a neutrino experiment under construction, with a near detector at Fermilab and a far detector at the Sanford Underground Research Facility that will observe neutrinos produced at Fermilab. An intense beam of trillions of neutrinos from the production facility at Fermilab (in Illinois) will be sent over a distance of 1,300 kilometers (810 mi) with the goal of understanding the role of neutrinos in the universe. More than 1,000 collaborators work on the project. The experiment is designed for a 20-year period of data collection. The primary science objectives of DUNE are The science goals are so compelling that the 2014 Particle Physics Project Prioritization Panel (P5) ranked this as "the highest priority project in its timeframe" (recommendation 13). The importance of these goals has led to proposals for competing projects in other countries, particularly the Hyper-Kamiokande experiment in Japan, scheduled to begin data-taking in 2027. The DUNE project, overseen by Fermilab, has suffered delays to its schedule and growth of cost from less than $2B to $3B, leading to articles in the journals Science and Scientific American described the project as "troubled." As of 2022, the DUNE experiment has a neutrino-beam start-date in the early-2030's, and the project is now phased.
The beamline for DUNE is called the "Long Baseline Neutrino Facility" (LBNF). The final design calls for a 2.4 MW proton beam from the Main Injector accelerator to be targeted in the LBNF beamline to produce pions and kaons that are magnetically focused into a decay pipe via a magnetic horn where they decay to neutrinos. The neutrinos will travel in a straight line through the Earth, reaching about 30 kilometers (19 mi) underground near the mid-point, to arrive at the underground laboratory in Lead, South Dakota.
To point the neutrinos toward the underground laboratory, the beam must be directed into the earth at a steep angle. LBNF construction will include a 58-foot-high hill made of compacted soil, connecting to a 680-foot-long tunnel that will contain a 635-foot-long particle decay pipe. The hill is integral to the "improved tritium management [that is] a major focus on the design of this new, higher beam power facility." Tritium produced by beamlines at can enter the surface ground water, however rates at Fermilab are maintained at a level well below that allowed by regulations.
The DUNE far detector design is based on state-of-the-art Liquid Argon Time Projection Chamber (LArTPC) technology. The far detector will consist of a total volume of 70-kilotons of liquid argon located deep underground, 1.5 kilometers (4,850 ft) under the surface. The current design divides the liquid argon between four LArTPC modules with a "fiducial volume" (the volume usable for physics analysis, which is smaller than the total volume to avoid interactions near detector edges) of 10 kilotons each. About 800,000 tons of rock will be excavated to create the caverns for the far detectors.
Since LArTPCs are relatively new technology, extensive R&D and prototyping have been required. Prototype detectors are being constructed and tested at CERN. The first of the two prototypes, the single-phase ProtoDUNE (CERN experiment NP04), recorded its first particle tracks in September 2018. CERN's participation in DUNE marked a new direction in CERN’s neutrino’s research  and the experiments are referred to as part of the Neutrino Platform in the laboratory's research programme.
The MicroBooNE experiment and ICARUS experiment detectors are a pair of 100-ton-scale LArTPCs in the Fermilab program that also act as R&D platforms for DUNE detector development. These experiments have provided important input, but are more than 20 times smaller than the DUNE modules. MicroBooNE is the longest continuously-running LArTPC detector, having taken data from 2015 to 2021--a considerably shorter than time-period than the 20 years required for DUNE.
The DUNE near detector will be located on Fermilab site, downstream of LBNF, about 600 meters from where the neutrinos are produced. The DUNE near detector comprises three subdetectors that will sit side by side. The primary purpose is to monitor and characterize the beam as the neutrinos are created in the LBNF line, so as to make accurate predictions for interaction rates at the DUNE far detector.
The project was originally started as a US-only project called the Long Baseline Neutrino Experiment (LBNE); in around 2012–2014 a descope was considered with a near-surface detector to reduce cost. However, the Particle Physics Project Prioritization Panel (P5) concluded in its 2014 report that the research activity being pursued by LBNE "should be reformulated under the auspices of a new international collaboration, as an internationally coordinated and internationally funded program, with Fermilab as host". The LBNE collaboration was officially dissolved on January 30, 2015, shortly after the new collaboration recommended by P5 was formed on January 22, 2015. The new collaboration selected the name Deep Underground Neutrino Experiment (DUNE).
In response to the P5 call for more international involvement, as of 2022, scientists from over 30 countries are involved in the construction of LBNF and DUNE.  In 2017, the UK's Science and Technology Facilities Council (STFC) announced a £65M investment in DUNE and LBNF. By 2022, the international partners providing in-kind contributions also included CERN, Brazil, Switzerland and Poland and the total foreign contribution to the $3B project was $570M, or about 20%.
The 2016 Conceptual Design Report called for the first two far detector modules to be completed in 2024, the beam to be operational in 2026, and the final modules to be operational in 2027.
In November 2021, Department of Energy (DOE) Office of Science officials reported  to the High Energy Physics Advisory Panel that although DUNE had secured $570M in international funding, the total cost of the project had risen substantially from the original cost estimate of less than $2B. It was reported that DOE reviews held in January and June 2021 concluded that even a descoped version of the project consisting of only two far detectors and a near detector would exceed the DOE upper allowed range of total project cost growth of $2.75B. This triggered a DOE review to "reaffirm" the project and establish an improved cost range and schedule, planned for mid-2022. Due to a history of lower-than-requested congressional appropriations for the project, at the same November 2021 meeting, DOE presented a "conservative profile [for funding] that the Office of Science can support."
In March, 2022, DOE announced that the project would be completed in two phases. The plan for phasing was announced during the Snowmass Process, an exercise periodically organized by the Division of Particles and Fields (DPF) of the American Physical Society to plan the future of particle physics. Phase I would consist of the first two far detector modules, a subset of the near detector system, and the 1.2 MW beamline, to be completed by 2032 for the estimated $3B cost. Phase II would complete the full scope by adding the additional two far modules, completing the suite of subdetectors are the near site and upgrading the beam power to 2.4 MW. Phase II represents cost beyond the $3B estimate for phase I.
Physicists have expressed concern that the two phase plan may lead to DUNE falling far behind its primary competition, the Hyper-Kamiokande experiment, and that phase II may not ever be constructed.
In order to provide 1.2 MW of protons to LBNF, the second phase of the Proton Improvement Project ("PIP II"), which will increase proton delivery from the Fermilab accelerator chain by 60%, must be completed. The cost of this Fermilab upgrade as of 2022 is $1.28B. Thus, the PIP II and DUNE Phase I combined costs exceed $4B. The PIP II project received approval to begin construction in April 2022 and is expected to be completed by 2028.
The Sanford Underground Research Facility makes use of, and is extending, the facilities of the Homestake Mine (South Dakota), which ceased operations at the end of 2001, to accommodate the far detector modules. Excavation of the DUNE far detector cavities began on July 21, 2017. Rock removed from underground is deposited in the Open Cut in the center of the city of Lead, South Dakota. Project management for the construction is overseen by Fermilab.
In June 2021, plumes of dust rising from the Open Cut due to DUNE construction led to complaints from businesses, homeowners, and users of a nearby park. Complaints continued through spring 2022 without adequate response from Fermilab management, resulting in the South Dakota Science and Technology Authority shutting down excavation on March 31, 2022. An investigation ensued in which the Fermilab management team admitted to failures in protocols, and instigated new measures to prevent black dust from leaving the Open Cut.  With these assurances in place, Fermilab was allowed to resume rock dumping on April 8, 2022.