DUNE will require a large number of neutrinos, which will be created using extreme versions of two common ingredients: magnets and pencil lead.
What do you need to create the world’s most powerful neutrino beam? Only a few magnets and some pencil lead are required. But not ordinary household items. Because this is the world’s most powerful high-energy neutrino beam, we’re dealing with colossal components like park bench magnets and ultrapure graphite rods the size of Danny DeVito.
Experiments in physics that push the boundaries of human understanding tend to work at extremes: the largest and tiniest scales, the highest intensities. The international Deep Underground Neutrino Experiment, hosted by the Department of Energy’s Fermilab, meets all three criteria. The experiment brings together over 1000 people from more than 30 nations to address issues that have kept many people awake at night: Why is there matter in the cosmos but no antimatter or no matter at all? Do protons, one of the atoms’ (and our) building blocks, ever decay? What causes black holes to form? And did I forget to turn off the stove?
Perhaps not the last
DUNE will investigate mysterious subatomic particles known as neutrinos, which are neutral, wispy wraiths that rarely interact with matter. Scientists will develop massive particle detectors to collect and analyze neutrinos since they are so antisocial. More matter inside the DUNE detectors implies more opportunities for neutrinos to interact, and these massive neutrino traps will hold 70,000 tons of liquid argon. They’ll be insulated from interfering cosmic rays at the Sanford Underground Research Facility in South Dakota, where they’ll be 1.5 kilometers below the surface—though neutrinos will have no issue traveling past that buffer and striking their target. The detectors can capture interactions from a precisely focused beam of neutrinos and pick up neutrinos from exploding stars that may grow into black holes.
Neutrinos (and their antimatter cousins, antineutrinos) are created as other particles decay, transporting little quantities of energy away to keep the cosmic ledger balanced. They come in large quantities from stars like our sun, the inside of Earth, and even the potassium in bananas. However, throwing fruit toward South Dakota would be difficult if you wanted to create trillions of high-energy neutrinos every second and transport them to a particle detector deep down.
The particle accelerator facility at Fermilab plays a role in this
Particles are sent through a succession of accelerators at Fermilab, each of which adds a burst of speed and energy. The complex is undergoing an update, which will feature a new linear accelerator at the start of the journey: PIP-II. This is the first accelerator project in the United States to receive significant international support, and it will accelerate particles to 84 percent the speed of light while traveling the length of two football fields. Particles then proceed to the Booster Ring for another… well, boost, before arriving at Fermilab’s most powerful accelerator, the Main Injector.
What’s the catch? The particle accelerators at Fermilab produce protons, which are valuable particles but not the ones that neutrino physicists are interested in studying.
So, how are scientists planning to convert Fermilab’s initial megawatt beam of protons into the billions of high-energy neutrinos needed for DUNE every second? This necessitates some additional infrastructure: The LBNF stands for Long-Baseline Neutrino Facility. Long baseline implies LBNF’s neutrinos will travel a long distance—1300 kilometers from Fermilab to Sanford Lab—and neutrino facility means… let’s produce some neutrinos.
Step 1: Take a handful of protons
The first stage is to suck particles from the Main Injector, as the circular accelerator would otherwise behave like a merry-go-round. A new beamline will need to be built and connected by engineers. With all the utilities, other beamlines, and Main Injector magnets in the way, that’s no easy task.
Elaine McCluskey, the LBNF project manager at Fermilab, says it’s in one of the most trafficked regions of the Fermilab accelerator complex. Some utilities will be moved out of the way during site preparation work at Fermilab, which will begin in 2019. When it comes time to build the LBNF beamline, the accelerator complex will be turned off momentarily.
Crews will safely relocate part of the Main Injector magnets and punch through the accelerator’s casing. They’ll build a new extraction region and beam containment, then replace the Main Injector magnets with Fermilab-built kicker magnets to modify the beam’s trajectory. They’ll also construct the new LBNF beamline, which will have 24 dipole and 17 quadrupole magnets, the majority of which will be produced by India’s Bhabha Atomic Research Centre.
Step 2: Set a goal
Neutrinos are a perplexing particle. They can’t be directed by magnetic fields the way charged particles (like protons) can because they’re neutral. When a neutrino is born, it continues in the same direction it was travelling before, like a child on the world’s longest Slip ‘N Slide. This feature makes neutrinos excellent cosmic messengers, but it also implies that Earthbound engineers must take an extra step: targeting.
Crews will drape the LBNF beamline over the contour of an 18-meter-high hill as they construct it. The protons will be directed toward the DUNE detectors in South Dakota as they descend the slope. Once the neutrinos have been formed, they will proceed in the same direction without the need for a tunnel.
Accelerator operators will be able to steer protons along the new beamline, similar to switching a train on a track, once all of the magnets are in place and everything is locked up tight. Instead of pulling into a station, the particles will slam into a target at full speed.
Step 3: Squash everything
The goal is a critical engineering component. It’ll most likely be a 1.5-meter-long rod of pure graphite—imagine your pencil lead on steroids—while it’s still being designed.
It will be housed inside the target hall, a sealed room filled with gaseous nitrogen, along with some other equipment. DUNE will begin with a proton beam capable of producing more than 1 megawatt of power, with ambitions to increase this to 2.4 megawatts in the future. Almost everything being built for LBNF is made to resist the increased beam intensity.
Because of the unprecedented beam power, manipulating anything inside the sealed hall will almost certainly necessitate the assistance of some robot pals operating from outside the thick walls. Engineers at KEK, Japan’s high-energy accelerator research group, are developing prototypes for parts of the sealed LBNF target hall.
The high-powered stream of protons will enter the target hall and smash into the graphite, depositing their energy and releasing a spray of new particles, chiefly pions and kaons, like bowling balls hitting pins.
“These targets have a very hard life,” says Chris Densham, group leader for high-power targets at STFC’s Rutherford Appleton Laboratory in the UK, which is in charge of the one-megawatt beam’s target design and manufacture. “In a few microseconds, each proton pulse causes the temperature to rise by a few hundred degrees.”
In a Goldilocks scenario, the LBNF target will operate at roughly 500 degrees Celsius. Engineers will need to remove excess heat since graphite functions better when it is hot, but not too hot. They can’t, however, let it get too chilly. Water, which is already utilized in some target designs, would provide too much cooling, thus RAL scientists are working on a new technique. The present proposed architecture circulates gaseous helium, which by the time it exits the system will be flying at around 720 kilometers per hour—the speed of a cruising airliner.
Step 4: Concentrate on the debris
Devices known as focusing horns take over as protons strike the target and produce pions and kaons. The pions and kaons are electrically charged, and the spray is directed back into a focussed beam by these massive magnets. The particle pathways will be corrected and aimed at the detectors at Sanford Lab using a series of three horns that will be designed and fabricated at Fermilab.
The target—a cylindrical tube—must sit inside the first horn, cantilevered into place from the upstream side, for the design to operate. This poses some challenging technical problems. It all comes down to striking a balance between what physicists want (a longer target that can last longer) and what engineers can produce. The target is only a few centimeters in diameter, and every incremental centimeter of length increases the chances of it drooping under the assault of protons and the gravitational pull of Earth.
Physicists don’t want the target to touch the sides of the horn, much like in a game of Operation.
The metallic horns receive a 300,000-amp electromagnetic pulse around once per second to form the concentrating field, which delivers more charge than a violent lightning bolt. If you were standing next to it, you’d want to put your fingers in your ears to block out the noise—and nothing, including graphite, should get close to touching the horns. Engineers may support the target from both sides, but this would complicate the inevitable removal and replacement.
Densham advises, “The simpler you can make it, the better.” “The temptation is always to design something clever and convoluted, but we want to make it as simple as possible so there are less things that might go wrong.”
Step 5: Physics takes place
The pions and kaons exit the target hall and pass through a 200-meter-long tunnel filled with helium after being focused into a beam. They decay as they do so, giving birth to neutrinos and other particles. The horns can also be switched to focus particles with the opposite charge, which decay into antineutrinos. Shielding at the tunnel’s end absorbs the extra particles, allowing the neutrinos or antineutrinos to continue on unaffected through soil and rock to their destination in South Dakota.
“LBNF is a complicated project with a lot of moving parts,” explains Jonathan Lewis, project manager for the LBNF Beamline. “It’s the lab’s future, the field’s future in the United States, and an intriguing and hard project,” she says. The prospect of discovering neutrino properties is thrilling science.”
Now is the time for science.
DUNE scientists will analyze the neutrino beam shortly after it is produced at Fermilab, using a powerful particle detector stationed exactly in the beam’s path. The majority of neutrinos, like all stuff, will flow right past the detector. However, a small percentage will collide with atoms inside the DUNE near-site detector, providing useful information on the neutrino beam’s composition as well as high-energy neutrino interactions with matter.
Then it’s time to bid the other neutrinos goodnight. Be quick—their 1300-kilometer trip at near-light speed will take four milliseconds, less than the time it takes to blink your eye. The job for DUNE scientists, on the other hand, will just begin now.Step 3: Squash everything
The goal is a critical engineering component. It’ll most likely be a 1.5-meter-long rod of pure graphite—imagine your pencil lead on steroids—while it’s still being designed.
It will be housed inside the target hall, a sealed room filled with gaseous nitrogen, along with some other equipment. DUNE will begin with a proton beam capable of producing more than 1 megawatt of power, with ambitions to increase this to 2.4 megawatts in the future. Almost everything being built for LBNF is made to resist the increased beam intensity.
Because of the unprecedented beam power, manipulating anything inside the sealed hall will almost certainly necessitate the assistance of some robot pals operating from outside the thick walls. Engineers at KEK, Japan’s high-energy accelerator research group, are developing prototypes for parts of the sealed LBNF target hall.
The high-powered stream of protons will enter the target hall and smash into the graphite, depositing their energy and releasing a spray of new particles, chiefly pions and kaons, like bowling balls hitting pins.
“These targets have a very hard life,” says Chris Densham, group leader for high-power targets at STFC’s Rutherford Appleton Laboratory in the UK, which is in charge of the one-megawatt beam’s target design and manufacture. “In a few microseconds, each proton pulse causes the temperature to rise by a few hundred degrees.”
In a Goldilocks scenario, the LBNF target will operate at roughly 500 degrees Celsius. Engineers will need to remove excess heat since graphite functions better when it is hot, but not too hot. They can’t, however, let it get too chilly. Water, which is already utilized in some target designs, would provide too much cooling, thus RAL scientists are working on a new technique. The present proposed architecture circulates gaseous helium, which by the time it exits the system will be flying at around 720 kilometers per hour—the speed of a cruising airliner.
Step 6: Concentrate on the debris
Devices known as focusing horns take over as protons strike the target and produce pions and kaons. The pions and kaons are electrically charged, and the spray is directed back into a focussed beam by these massive magnets. The particle pathways will be corrected and aimed at the detectors at Sanford Lab using a series of three horns that will be designed and fabricated at Fermilab.
The target—a cylindrical tube—must sit inside the first horn, cantilevered into place from the upstream side, for the design to operate. This poses some challenging technical problems. It all comes down to striking a balance between what physicists want (a longer target that can last longer) and what engineers can produce. The target is only a few centimeters in diameter, and every incremental centimeter of length increases the chances of it drooping under the assault of protons and the gravitational pull of Earth.
Physicists don’t want the target to touch the sides of the horn, much like in a game of Operation.
The metallic horns receive a 300,000-amp electromagnetic pulse around once per second to form the concentrating field, which delivers more charge than a violent lightning bolt. If you were standing next to it, you’d want to put your fingers in your ears to block out the noise—and nothing, including graphite, should get close to touching the horns. Engineers may support the target from both sides, but this would complicate the inevitable removal and replacement.
Densham advises, “The simpler you can make it, the better.” “The temptation is always to design something clever and convoluted, but we want to make it as simple as possible so there are less things that might go wrong.”
Step 7: Physics takes place
The pions and kaons exit the target hall and pass through a 200-meter-long tunnel filled with helium after being focused into a beam. They decay as they do so, giving birth to neutrinos and other particles. The horns can also be switched to focus particles with the opposite charge, which decay into antineutrinos. Shielding at the tunnel’s end absorbs the extra particles, allowing the neutrinos or antineutrinos to continue on unaffected through soil and rock to their destination in South Dakota.
“LBNF is a complicated project with a lot of moving parts,” explains Jonathan Lewis, project manager for the LBNF Beamline. “It’s the lab’s future, the field’s future in the United States, and an intriguing and hard project,” she says. The prospect of discovering neutrino properties is thrilling science.”
Now is the time for science
DUNE scientists will analyze the neutrino beam shortly after it is produced at Fermilab, using a powerful particle detector stationed exactly in the beam’s path. The majority of neutrinos, like all stuff, will flow right past the detector. However, a small percentage will collide with atoms inside the DUNE near-site detector, providing useful information on the neutrino beam’s composition as well as high-energy neutrino interactions with matter.
Then it’s time to bid the other neutrinos goodnight. Be quick—their 1300-kilometer trip at near-light speed will take four milliseconds, less than the time it takes to blink your eye. The job for DUNE scientists, on the other hand, will just begin now.
Scientists will use their massive particle detectors in South Dakota to measure neutrinos once more. Researchers will compile massive amounts of data, investigate how neutrinos vary, and attempt to solve some of the numerous neutrino mysteries, such as which of the three types of neutrinos is the lightest. Do neutrinos act similarly to antimatter neutrinos? And, most importantly, are neutrinos the key to understanding why matter triumphed over antimatter at the beginning of the universe?
These are high subjects, and scientists have been preparing for this massive task for quite some time. Short-distance experiments like MicroBooNE and MINERvA, as well as long-distance initiatives like NOvA and MINOS, have all been conducted at Fermilab. DUNE will benefit from the experience obtained in developing and running those experiments, just as LBNF will profit from the experience gained in creating the NuMI (Neutrinos from the Main Injector) beamline, which was developed to produce neutrinos for Fermilab’s and Minnesota’s MINOS detectors.
“We had never built anything like the NuMI beamline before at Fermilab, and it allowed us to learn a lot about how to create neutrinos, run a beamline efficiently, and repair components,” McCluskey says. “A number of individuals who worked on that beamline are constructing the new one and applying those lessons to provide DUNE an effective, efficient, and unprecedented beam power.”
That’s how the world’s most powerful neutrino beam is created.