Gold mines don’t usually get a second act. When the ore runs out, the pumps shut down, the shafts flood, and the town next door pivots to selling T-shirts. Homestake, in Lead, South Dakota, ran longer than almost any of them: 125 years of continuous digging, more than 40 million ounces of gold, and workings that eventually reached 8,000 feet below town, the deepest mine in the Western Hemisphere by the time it closed in 2001.<\/p>\n
It was also the operation that made George Hearst rich after he bought the claim in 1877, money that later helped bankroll his son William Randolph’s newspaper empire. The company’s stock sat on the New York Stock Exchange longer than any listing in the exchange’s history.<\/p>\n
So the mine has been a lot of things. What it has never been is a place where steel goes down instead of gold coming up. This summer, crews in Lead are lowering 10 million pounds of structural steel into the old workings, one elevator load at a time, to build the frames for two of the largest cryogenic tanks ever attempted, 4,850 feet below the surface.<\/p>\n
The steel belongs to the Deep Underground Neutrino Experiment<\/a>, or DUNE, hosted by Fermilab in Illinois. Fermilab calls it the largest scientific project supported by the Department of Energy’s Office of Science, and the largest in the United States. The physicists get the caverns in a few years. Right now, the place belongs to ironworkers and hoist operators.<\/p>\n On May 7, Fermilab and the Sanford Underground Research Facility, the lab that now occupies the old mine, held a ceremony in Lead marking the start of the move. Senior Department of Energy officials, members of Congress and CERN leadership all turned up, and everyone got to sign one of the beams before it heads underground for good. Fermilab Director Norbert Holtkamp called the moment “the start of a pivotal phase for DUNE.”<\/p>\n The steel itself came from CERN, the European lab best known for the Large Hadron Collider, as an in-kind contribution. According to Fermilab, it’s the first time CERN has invested in infrastructure for an experiment outside Europe. The arrangement runs both ways, since American national labs are building superconducting magnets for CERN’s upgraded collider in return.<\/p>\n The full 10 million pounds is scheduled to be underground and prepped for installation over the course of this summer. Which sounds simple enough until you look at the route.<\/p>\n There are no trucks driving down to the 4,850-foot level. Every piece of DUNE’s support structure travels through the Ross Shaft, one of the mine’s two main shafts, which crews spent years rehabilitating for exactly this job. If a component doesn’t fit in the shaft, it doesn’t exist as far as this project is concerned.<\/p>\n Last fall, SURF installed a purpose-built conveyance for the beams: a cage with a floor measuring 4.5 by 5 feet and sides 60 feet high, fitted with an internal hoist that lifts each beam vertical and locks it in place. The beams make the trip standing upright.<\/p>\n In April, crews ran the first full test<\/a>. A 43-foot beam weighing more than 15,890 pounds rolled into the Ross Headframe on rails, got rigged to the winch inside the cage and was lifted into position. The whole operation took about 18 minutes.<\/p>\n SURF says that beam is one of roughly 2,100 structural components making the same trip, and Fermilab’s far detector project manager expects crews to repeat lifts like it hundreds of times. At 18 minutes a lift, you can do the math on how a summer disappears.<\/p>\n The structures those beams form will each measure 216 feet long, 62 feet wide and 60 feet high, which Fermilab describes as roughly the size of a five-story building. Inside each one goes a cryostat, a giant thermos built to hold 17,000 tons of liquid argon at about minus 300 degrees Fahrenheit.<\/p>\n Nobody sells tanks like that off a shelf. So CERN contracted GTT, the company that designs containment systems for ships carrying liquefied natural gas, and the DUNE cryostats use the same membrane technology<\/a> that keeps LNG liquid on a tanker crossing an ocean. GTT has been designing smaller cryostats for CERN since 2007.<\/p>\n The design details are where it gets fun. The innermost layer is a corrugated stainless steel membrane, and the corrugations are not decoration. When the tank cools from room temperature down to argon temperature, a drop of roughly 375 degrees Fahrenheit, a smooth liner would shrink by about 20 inches along its length and rip its own welds apart. The corrugations flex instead, and the welds hold.<\/p>\n The inner portions of each cryostat alone require more than 5,000 individual pieces, every one of them sized for the shaft. “It’s the first time we will do something this big,” said Llu\u00eds Miralles Verge, who leads the cryostat project at CERN. Each finished tank encloses nearly 500,000 cubic feet, about the volume of five Olympic swimming pools.<\/p>\n Then comes the argon itself, a liquid 1.4 times denser than water. Filling the tanks means about five 18-ton tanker deliveries per day at the site, with the argon piped down as gas and recondensed into liquid at the bottom. If hauling delicate cargo at brutal temperatures sounds like a familiar genre, it’s the same obsession that got Europe’s Antarctic ice cores across the equator at minus 58 degrees<\/a> without thawing a single air bubble.<\/p>\n The reason for all the depth is straightforward. Neutrinos barely interact with anything, which is why physicists call them ghost particles. Cosmic rays hammer the surface constantly and would bury the faint signals the experiment is after. A mile of Black Hills rock filters out the noise.<\/p>\n Homestake learned that lesson before almost anyone. In 1965, a Brookhaven chemist named Ray Davis talked the mining company into excavating a cavern on the same 4,850-foot level, then installed a 100,000-gallon tank of perchloroethylene<\/a>, ordinary dry-cleaning fluid, to catch neutrinos streaming out of the sun.<\/p>\n Davis found them, but only about a third as many as theory predicted. That mismatch, known as the solar neutrino problem, hung over physics for decades until it turned out the neutrinos were changing type mid-flight. Davis had been right all along, and in 2002 he shared the Nobel Prize in Physics for it.<\/p>\n The mine shut down around that same era, the National Science Foundation picked it as the site for a national underground lab in 2007, and between 2021 and 2024 crews blasted out 800,000 tons of rock to carve two seven-story caverns plus a third for utilities. America has a habit of keeping its most interesting machines out of sight. The country’s only fully digital nuclear reactor runs in a basement at Purdue<\/a>.<\/p>\n There’s a reason nobody is improvising any of this. Once the detectors are assembled inside the cryostats, filled with argon and sealed, Fermilab says scientists won’t have access to the submerged components for decades. Whatever goes in has to work on the first try, unattended, for a very long time.<\/p>\n So while the steel goes down in South Dakota, a 770-ton prototype called ProtoDUNE is being deliberately stressed at CERN<\/a>. Since May 22, the team has been holding the detector’s newest design at full operating voltage to see what gives, a test scheduled to run into the fall. “We are taking that same concept and scaling it up to 300,000 volts,” said Steve Kettell, one of DUNE’s technical coordinators, comparing the electric field to what a 1.5-volt household battery does on a much smaller scale.<\/p>\n That newer design swaps the traditional wire-plane detectors, which required wrapping wire 3,000 times around a frame, for channels of copper printed on circuit boards, the same basic technology inside a computer keyboard. Fermilab reported on July 27 that the prototype ran smoothly through commissioning and is now being pushed hard on purpose.<\/p>\n The Illinois end is moving too. On July 9, Fermilab crews placed the first beamline component of PIP-II, the new linear accelerator that will eventually generate the neutrino beam, into its tunnel outside Chicago.<\/p>\n Fermilab’s stated priority is to deliver the first neutrino beam to DUNE by 2031, fired 800 miles through solid earth from Illinois to South Dakota. No tunnel is required, because neutrinos pass through the planet as if it were barely there. Two more detector modules may follow from international partners after the first pair.<\/p>\n The honest caveat is that this project’s schedule has moved before. Construction setbacks pushed earlier timelines back, and the Department of Energy split the megaproject into two phases<\/a>, as Scientific American has chronicled. So 2031 is a target with a lot of steel between here and there, and the physics starts when the beam does.<\/p>\n The steel is on a tighter deadline. It has an elevator to catch, all summer long.<\/p>\n","protected":false},"excerpt":{"rendered":" Gold mines don’t usually get a second act. When the ore runs out, the pumps shut down, the shafts flood, … <\/p>\nThe steel started moving in May<\/h2>\n
Everything rides one elevator<\/h2>\n
The tanks are borrowed from LNG shipping<\/h2>\n
This mine has caught neutrinos before<\/h2>\n
A prototype in Europe is holding 300,000 volts right now<\/h2>\n
What 2031 actually means<\/h2>\n