How can you study a particle that’s almost invisible? For the last decade, Justin Evans at the University of Manchester has been asking this question.
“The neutrino is clearly a weird particle,” said Evans. “It’s so light we haven’t even measured its absolute mass.”
Neutrinos are some of the most abundant particles in the universe, yet little is known about them because they evade conventional detection methods. When the United Kingdom joined the Deep Underground Neutrino Experiment in 2015, Evans saw an opportunity.
“We were thinking about what the UK could do for DUNE,” he said. “We wanted to have a big impact and make a key part of the detector.”
Unpacking a particle detector device known as APA for testing at CERN. APAs are key components for the international Deep Underground Neutrino Experiment, to be assembled in the United States. Photo: Julien Marius Ordan and Maximilien Brice, CERN
On Oct. 15, a large wooden box from Daresbury Laboratory in the United Kingdom arrived at the CERN Neutrino Platform. Inside was the first anode plane assembly, a key component in the DUNE Far Detector, to be mass-produced for DUNE.
“It is the first of 130 APAs that the UK will deliver, which will ultimately be installed in the first of the DUNE modules at South Dakota,” said DUNE spokesperson Stefan Söldner-Rembold. “As such, it is the first major component of the DUNE Far Detector to be built.”
More than 1,400 scientists and engineers in over 30 countries contribute to the experiment. Their goal is to paint a clearer picture of the origin of matter and how the universe came to be. DUNE will measure how neutrinos and antineutrinos behave during an 800-mile journey from the U.S. Department of Energy’s Fermi National Accelerator Laboratory near Chicago to Sanford Underground Research Facility in Lead, South Dakota. Because these particles and their antimatter counterparts rarely interact with matter, they will pass directly through the earth before arriving at massive subterranean particle detectors that have a total volume equivalent to about 22 Olympic-size swimming pools and will be filled with 70,000 tons of liquid argon. These gigantic detectors will allow scientists to study the differences in behavior between neutrinos and antineutrinos. The results will shed light on the role neutrinos played in the evolution of the universe.
Scientists can reconstruct what happened during a neutrino-argon collision based on when and where the released electrons are detected on an APA wire plane made from 15 miles of hair-thin wire. Photo: Julien Marius Ordan, CERN
The APAs build on an idea originally developed by Nobel Laureate Carlo Rubbia and other scientists in the 1970s. In each APA, 15 miles of hair-thin wire are wrapped in four different directions around a support structure the size of a church door. Electrons released from a neutrino colliding with an argon atom are pulled toward the wires by a strong electric field. Scientists then can reconstruct what happened during the original neutrino-argon collision based on when and where the released electrons intersect with the wires.
“We were thinking about what the UK could do for DUNE. We wanted to have a big impact and make a key part of the detector.” – Justin Evans
Even though this technique for detecting neutrinos has been around for decades, adapting it for DUNE—which will be built one mile underground to shield the detectors from cosmic rays that hit Earth’s surface—was a challenge.
“That’s the ship-in-the-bottle aspect of underground physics,” said Evans. “Everything has to go down in chunks smaller than the mine shaft.”
The final APA design comes after a successful two-year run of a prototype of the DUNE detector, known as ProtoDUNE, located at the CERN Neutrino Platform. These final DUNE-production APAs only have slight modifications from the original prototypes.
“We realized that we needed to make some of the tubes that hold the cables bigger,” Evans said. “There were also some screws that were hard to reach. It was quite boring and mundane things, but that’s good—you want it to be the boring and mundane things.”
Another consideration was creating an APA blueprint that is suitable for mass production of 150 APAs on both sides of the Atlantic: 130 from the UK and an additional 20 from the U.S.
“We needed a design that is robust enough that we can make 150 of them,” said Hannah Newton, the project manager coordinating the APA production at Daresbury Laboratory. “There’s no more tinker time.”
Over the next few months, three more APAs will arrive at the CERN neutrino platform for final testing inside the ProtoDUNE-SP cryostat during early 2022, with plans for mass production to start up in spring. Once produced, all APAs will be shipped to South Dakota for installation.
“The cold electronics testing inside ProtoDUNE will be the final proof that the all the systems integrate with one another,” Newton said. “It’s the final assurance that we’re good to go and can ramp up production.”
Fermilab is the host laboratory for DUNE, in partnership with funding agencies and scientists from around the world.
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
Cost- and energy-efficient rapid cycling magnets for particle accelerators are critical for particle physics research. Their performance determines how frequently a circular particle accelerator can receive a bunch of particles, propel them to higher energy, send them to an experiment or target station, and then repeat all over again.
A small team of physicists, engineers and technicians at the U.S. Department of Energy’s Fermi National Particle Accelerator Laboratory, led by Henryk Piekarz, just demonstrated the world’s fastest magnetic ramping rates for particle accelerator magnets. Noteworthy, they achieved this record by using magnets made with energy-efficient, high-temperature superconducting material.
What is the best conductor?
Despite the many attractive features of superconducting wire, the fastest-ramping high-energy particle accelerators still use magnets with copper conductors operating at room temperature. Examples include the 3 GeV proton ring at JPARC in Japan, which features a magnetic field that changes at a rate of 70 tesla per second (T/s) and reaches a peak magnetic field of 1.1 tesla, and the 8 GeV Booster ring at Fermilab, which achieves a ramping rate of 30 T/s and a peak field of 0.7 tesla.
Henryk Piekarz of Fermilab’s Accelerator Division controls the flow of cryogens in the high-temperature superconductor magnet prototype. Photo: Ryan Postel, Fermilab
Most of the powerful superconducting magnets employed in modern-day particle accelerators are relatively slow when it comes to increasing the magnetic field. Their main goal is to ramp up to a high peak magnetic field to steer particles around a ring while electric fields propel the particles to higher and higher energy. The higher the energy, the stronger the magnetic field must be to keep the particles in their track as they go around the ring.
Fermilab’s Tevatron accelerator was the first machine based on superconducting steering magnets. The ramping of the 4.4 tesla magnets to full magnetic strength took more than a minute and a half, while electric fields increased the energy of the particles to 1 TeV. Today, the world’s most powerful accelerator, the Large Hadron Collider at CERN, uses superconducting steering magnets that ramp up to almost 8 tesla in approximately 20 minutes, while the accelerator propels particles to 6.5 TeV. This corresponds to a ramping rate of about 0.006 T/s and is much slower than the ramping rate of conventional accelerator magnets operating at room temperature.
A team at Fermilab has demonstrated the world’s fastest magnetic ramping rates for particle accelerator magnets. Noteworthy, they achieved the record by using energy-efficient, high-temperature superconducting tape.
Now, a superconducting accelerator test magnet is taking the ramping rate lead as Fermilab’s high-temperature superconductor test magnet has yielded rates of up to 290 T/s, while achieving a peak magnetic field strength of about 0.5 tesla. The results have been published on the arXiv and reported at the 27th International Conference on Magnet Technology by the IEEE Council on Superconductivity this month. Piekarz and his colleagues hope to achieve even higher magnetic field strength by increasing the electrical current running through the magnet, while maintaining the superior ramping rate.
The solution: high-temperature superconductor
Two major problems are limiting the magnetic ramping rate in “low-temperature” superconducting accelerator magnets now in common use. The first one is the heating of the superconductor during ramping, due to eddy currents that can create large heat depositions in the superconductor. This heating rapidly increases with the increase of field amplitude and the ramping rate. The second one is the very small margin for temperature variation in the traditional low-temperature superconductors, such as niobium-titanium and niobium-tin, which are used in most modern superconducting accelerator magnets. Even a small increase in temperature can lead to the undesirable transition of a superconducting magnet into its normal conducting, resistive state.
A dual-aperture, high-temperature superconductor accelerator magnet test set-up. Photo: Ryan Postel, Fermilab
The solution to these problems is to employ the unique properties of “high-temperature” superconducting material known as YBCO. Using this material, Piekarz and his team designed a magnet and operated it at temperatures between 6 and 20 K and up to 1,000 amps of electrical current.
The peak strength of the magnetic field achieved during the record-setting ramping tests was limited by the electrical current provided by the power supply used in the test. Piekarz and his team plan to expand the power supply capabilities in the future, possibly achieving even higher rates, as they will carry out further studies on the ultimate capabilities of this advanced magnet technology.
The development of these fast-cycling magnets is critical for future neutrino research, featuring rapid-cycling proton synchrotrons, particle injectors for the proposed Future Circular Collider, and the design of pulsed muon colliders.
Their research was supported through the Laboratory Directed Research and Development program, an initiative established to foster innovative scientific and engineering research at Department of Energy national laboratories.
Fermi National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.