DOE Weighs Its Options for Underground Lab

By Michael Lucibella

A now defunct gold and silver mine in South Dakota was all set to host a next generation underground science lab until the National Science Foundation backed out. The Department of Energy is working to save the biggest physics experiments, but because of the uncertain nature of future budgets, it is unclear how much will ultimately be built.

The DOE and the NSF had planned to jointly build and operate the expansive underground lab in the Homestake mine in Lead, South Dakota. In December, following a directive from its oversight body, the National Science Board, the NSF unexpectedly pulled out of the project, citing concerns over the cost and their broad role in running the lab. This halted the project, and the Department of Energy had to go back to the drawing board and rethink its plans for the site.

The original plan for the Deep Underground Science and Engineering Laboratory, known as DUSEL, featured a massive multidisciplinary lab at multiple levels in the mine. In addition to physics, the lab would have had facilities for biological, geological and structural engineering experiments. That comprehensive vision is essentially dead. The DOE is mulling over how to move forward and build the three biggest physics experiments planned for the mine.

The biggest hurdle facing the facility, now officially known as Sanford Underground Research Facility at Homestake, is that of funding. According to a recent report by the Department of Energy that reviewed the proposed experiments, the total cost for the facility would likely come to around two billion dollars.

The three experiments the DOE is still considering would probe some of the most fundamental questions about the makeup of the universe. The experiments would look to directly detect dark matter through a third-generation dark matter detector, attempt to determine if a neutrino is its own antiparticle by looking for neutrinoless double beta decays, and hunt for evidence of CP violations in neutrino oscillations.

The DOE report looked at multiple construction options for the deployment of these experiments. Possible plans ranged from locating all of the experiments as deep as 7,400 feet underground, 4,850 feet or as shallow as 800 feet, installing different experiments at different levels, or building some of them in existing labs in other parts of the world.

“We were asked to evaluate what it would take if the DOE wanted to do the three experiments at what would be DUSEL,” said study chair Jay Marx of Caltech and executive director of LIGO. He added that they were charged “just to gather information and evaluate the cost, the time scale and the technical risks.”

The report concluded that if the experiments were to be located in the South Dakota mine, bundling the experiments on the same underground level would save a lot of money because they could share infrastructure such as electricity, utilities and mine shafts. It also found that while dollar for dollar it would likely be cheapest to locate the dark matter experiment or double beta decay experiments in Ontario’s SNOLAB, there are other less tangible benefits for basing the experiments in the United States.

“Locating the facility in the US would help to promote US leadership in these fields for the foreseeable future,” the report read.

The Long Baseline Neutrino Experiment is the focus of much scrutiny. While the dark matter and double beta decay experiments could conceivably be located at a different facility, the neutrino experiment is bound to Homestake because it relies on a stream of neutrinos from Fermilab.

The design of the neutrino detector is still up in the air. The two competing designs would use either a water Cherenkov detector or a liquid argon-based detector. Water detectors are a long established technology for detecting neutrinos, while liquid argon is much newer and unproven. The report was largely critical of the proposed liquid argon detectors. If the liquid argon technology did prove to work, the report said it would still take a substantial amount of funding until at least 2015 to complete the necessary research and development to create the detectors.

The DOE report is complemented by a second study, done by the National Research Council (NRC), that came out at about the same time. “In our view, the LBNE, the long baseline neutrino experiment, is somewhat special,” said Andrew Lankford of the University of California, Irvine, who chaired the NRC study. “It’s not saying that it’s more important than the others, but it’s made special because there’s an intense neutrino source at Fermilab.”

The NRC’s report found that the three proposed experiments were a “top priority” and recommended that the experiments be pursued.

“Our first conclusion was that there were three extremely important experiments that we thought were of the utmost importance,” Lankford said. He added also that the NRC report and the DOE reports looked at different aspects of the planning of the lab. “They’re very complementary. Ours is to focus on the science assessments and the other issues that I call programmatic, while theirs focuses primarily on cost and technical issues.”

William Brinkman, the head of the DOE’s Office of Science, has said that he wants to go forward with the proposed experiments. However, what final form they may take is up in the air because of continued budget uncertainties. Whatever final budget is passed for the department will determine how the facility will ultimately be built.

“I am optimistic about things coming together,” said Kevin Lesko of the University of California Berkeley and DUSEL principal investigator. “I’m optimistic we have all the elements on hand to help the DOE decide how they want to go forward with the facility.”

Lesko added that despite the unexpected handoff, having the Department of Energy take over the operations of the facility wasn’t a bad thing because it has considerable experience running large national labs. “It’s a more natural role for the DOE to run such a facility.”

The Homestake Mine in Lead South Dakota is a sprawling web of underground chambers and tunnels at depths up to 8,000 feet. When the mine shut down in 2002, it was the largest and deepest mine in the country. After the shut down, water began flooding the lowest levels. Congress appropriated $15 million in funding to keep pumps running to keep upper levels dry and viable for any future science experiments.

“The science is absolutely first rate. The idea of putting things in the same place to share infrastructure and share intellectual excitement makes sense. It might not make sense for the biological or geological sciences because they have an interest in variability,” said Marvin Marshak of University of Minnesota, who founded the underground laboratory at the Soudan mine in Minnesota. “For the physics, which is really more interested in the experiments than characterizing the site, it makes a lot of sense.”

APS News reported on the NSF pullout in the January issue, and featured a Back Page on DUSEL/SURF by Kevin Lesko in the July issue.