Particle searches depend on UW-Madison engineers
A 30-minute film about IceCube, Chasing the Ghost Particle: From the South Pole to the Edge of the Universe, will screen Wednesday, January 22 at 7 p.m. at the Marquee in Union South.
Before the cosmic neutrinos came, there were smaller discoveries: A particular brand of tape (fiberglass, with silicon adhesive) that holds up well in the harsh conditions at the South Pole. The best kinds of kind of cables to use when lowering neutrino-detection modules deep into Antarctic ice. The most efficient ways to heat water.
Terry Benson and his fellow engineers learned these and other “little tricks,” as Benson calls them, during their years of drilling for the IceCube Neutrino Observatory. The UW-Madison-operated particle-physics project made a major breakthrough in 2013, making its first observation of neutrinos from outside our solar system.
But even before that, IceCube gave engineers a body of knowledge that will greatly aid other projects seeking answers about neutrinos and dark matter. "We had a proof of concept to build off of, but this was a new level of engineering,” Benson says. “There is never a textbook way of building these things.”
Benson currently works as a staff engineer at the UW-Madison Physical Sciences Laboratory near Stoughton. He was earning his bachelor’s degree in mechanical engineering in 2003 when he signed up to help assemble the IceCube hot-water drill. The drill essentially blasts hot water into the ice, forming a hole about 2 feet across and a mile and a half deep. Then, crews lower into the hole a string of 60 digital optical modules, or DOMs, designed to detect neutrinos. The water in the hole freezes the DOMs into place, and the crew moves on to the next hole.
As a graduate student under Mechanical Engineering Professor John Moskwa, Benson used advanced modeling to develop water boilers that ran at about 95 percent efficiency. He also contributed to a sophisticated computer model of the entire drill system.
After earning his master’s degree, Benson became a full-time IceCube engineer, then eventually took his current job at PSL. Over the years, he has made eight trips to Antarctica to support IceCube and its companion neutrino project, the Askaryan Radio Array (ARA).
In his role at PSL, Benson—alongside colleagues Jeff Cherwinka, Darrell Hamilton and several others—continues to provide engineering and fabrication support for IceCube and other particle-physics projects.
Recently, he developed a different hot-water drill for the ARA. The ARA radio detectors aren’t meant to be frozen into place like the IceCube DOMs, so the ARA drilling system had to remove water from the holes before it could freeze back. Benson and his colleagues responded to this new hurdle by developing a drill that shoots water in and pumps it out simultaneously. The pump actually travels down into the hole along with the drill head, to a depth of about 650 feet.
Before IceCube, there wasn’t much precedent to draw on for this kind of work. But 86 very deep holes and seven working seasons later, there’s finally a wealth of data, trial-and-error, computer simulation, and workarounds for the many problems that afflict machines in brutally cold temperatures. Benson even gave a talk titled “Innovations in hot water drilling at the South Pole” during the annual Polar Technology Conference in 2013.
Just as importantly, there’s a bit more working experience in the world for such projects: Benson proudly notes that IceCube produced 30 of the world’s best hot-water drillers.
Neither the IceCube nor the ARA drill looks like a model of efficiency. Each comprises a chain of large sleds, carrying generators, water heaters, fuel tanks, a computer-control system, great lengths of hose, and the drill nozzle itself. (The massive hose reel for IceCube is one of the largest things ever built in the PSL shop, and an engineering feat in its own right.)
But the design teams have focused on fuel efficiency throughout, because it’s expensive to ship jet fuel to the South Pole. “We had to build a drilling strategy model to drill a hole that was big enough to allow time to get the equipment into the ice, but not too big, because that wastes fuel,” Benson says. “We need to continue looking at ways to increase energy efficiency so that fuel requirements stay low, and turning to more renewable forms of energy to power the experiments.“
The roughly 10 years of drilling at the South Pole will pay off in far less remote locations. Current PSL projects include engineering support for the LUX-ZEPLIN Dark Matter Search Experiment. For the project, researchers plan to use a huge chamber of liquid xenon a mile underground near Lead, South Dakota, to search for weakly interacting massive particles, or WIMPs.
“For me, personally, this project is one of the most interesting because it is exposing me to new engineering skills, such as cryogenics and extreme purity requirements,” Benson says. “Using xenon is a challenge in and of itself, because xenon is such a rare gas.”
Other particle-physics projects PSL is working on include the Fermilab Long Baseline Neutrino Experiment (LBNE), the Daya Bay Reactor Neutrino Experiment in China’s Guangdong Province, and the Compact Muon Solenoid, site of the historic Higgs boson discovery.
Even as engineers learn more and more about what works on these projects, each one presents its own formidable set of unknowns. “Part of what makes this line of work exciting for us is that it’s hard to know what new challenges will be coming our way,” Benson says.
At least one challenge is clear. Researchers need to help these projects become more and more efficient so that they can thrive in the long run. “Physicists and engineers always need to find new ways to deliver new science while staying within the confines of what is actually supportable and will be funded,” he says. “New drills need to be smaller, lighter and more mobile.”
By tackling these technical uncertainties, engineers like Benson help physicists explore even greater unknowns about the makeup of the universe.