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Posts Tagged ‘superconducting magnets’

This article appeared in Fermilab Today on May 1, 2015.

Fermilab Director Nigel Lockyer shakes hands with Jefferson Lab Director Hugh Montgomery by a superconducting coil and its development and fabrication team at Fermilab. Six coils have been made and shipped to Jefferson Lab for use in the CLAS12 experiment. Photo: Reidar Hahn

Fermilab Director Nigel Lockyer shakes hands with Jefferson Lab Director Hugh Montgomery by a superconducting coil and its development and fabrication team at Fermilab. Six coils have been made and shipped to Jefferson Lab for use in the CLAS12 experiment. Photo: Reidar Hahn

A group of Fermilab physicists and engineers was faced with a unique challenge when Jefferson Lab asked them to make the superconducting coils for an upgrade to their CEBAF Large Acceptance Spectrometer experiments. These are some of the largest coils Fermilab has ever built.

Despite obstacles, the sixth coil was completed, packed on a truck and sent to Jefferson Lab to become the last piece of the torus magnet in the lab’s CLAS detector. It arrived on Thursday.

The CLAS detector’s upgrade (CLAS12) will allow it to accept electron beams of up to 11 GeV, matching the beam energy of the Virginia laboratory’s CEBAF electron accelerator after five passes. These improvements will allow Jefferson Lab to more accurately study the properties of atomic nuclei.

A major component of the enhanced detector is the torus magnet, which will be made from the six superconducting coils created at Fermilab. Aside from cleaning, insulating and winding the coils, one of the most important parts of the process is vacuum epoxy impregnation. During this step, air and water vapor are removed from the coils and replaced with an epoxy.

This process is particularly difficult when you’re working on magnets as big as the CLAS12 coils, which are 14 feet long and seven feet wide. Fermilab’s Magnet Systems Department fabrication team, the group responsible for making these massive coils, encountered a major obstacle at the end of March 2014 after finishing the first practice coil.

What they found were dry areas within the coil where the epoxy couldn’t penetrate. These were places where the coils weren’t fixed into place, meaning they could move and generate heat and resistance. This can lead to magnet quench, the transition from superconducting to a normal state — a highly undesirable consequence.

The Fermilab group and Jefferson Lab staff collaborated to come up with a solution. By trying new materials, new temperature profiles and adjusting the time that the epoxy was left to sit and be adsorbed, the team was able to prevent the dry areas from forming.

Fred Nobrega, the lead engineer at Fermilab for the CLAS12 coil project, joined the effort last August.

“It was rewarding for me to join the project near its low point, be able to help get through the hurdle and see this completed,” he said.

Production has been steady since December, with Fermilab sending roughly one coil a month to Jefferson Lab. Although the sixth coil will become the last piece of the torus magnet, the project isn’t complete just yet — the ultimate goal is to make eight identical coils, the six for the magnet and two spares.

“We’re succeeding because we have great people and a productive collaboration with Jefferson Lab, who helped us at difficult moments,” said George Velev, head of the Magnet Systems Department. “We worked together on a tough problem and now we see the results.”

Diana Kwon

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This article appeared in Fermilab Today on April 3, 2015.

This magnet recently achieved an important milestone, reaching its design field of 11.5 Tesla. It is the first successful niobium-3-tin, twin-aperture accelerator magnet in the world. Photo: Sean Johnson

This magnet recently achieved an important milestone, reaching its design field of 11.5 Tesla. It is the first successful niobium-3-tin, twin-aperture accelerator magnet in the world. Photo: Sean Johnson

Last month, a new superconducting magnet developed and fabricated at Fermilab reached its design field of 11.5 Tesla at a temperature nearly as cold as outer space. It is the first successful twin-aperture accelerator magnet made of niobium-3-tin in the world.

The advancements in niobium-3-tin, or Nb3Sn, magnet technology and the ongoing U.S. collaboration with CERN on the development of these and other Nb3Sn magnets are enabling the use of this innovative technology for future upgrades of the Large Hadron Collider (LHC). They may also provide the cornerstone for future circular machines of interest to the worldwide high-energy physics community. Because of the exceptional challenges — Nb3Sn is brittle and requires high-temperature processing — this important milestone was achieved at Fermilab after decades of worldwide R&D efforts both in the Nb3Sn conductor itself and in associated magnet technologies.

Superconducting magnets are at the heart of most particle accelerators for fundamental science as well as other scientific and technological applications. Superconductivity is also being explored for use in biosensors and quantum computing.

Thanks to Nb3Sn’s stronger superconducting properties, it enables magnets of larger field than any in current particle accelerators. As a comparison, the niobium-titanium dipole magnets built in the early 1980s for the Tevatron particle collider produced about 4 Tesla to bend the proton and antiproton beams around the ring. The most powerful niobium-titanium magnets used in the LHC operate at roughly 8 Tesla. The new niobium-3-tin magnet creates a significantly stronger field.

Because the Tevatron accelerated positively charged protons and negatively charged antiprotons, its magnets had only one aperture. By contrast, the LHC uses two proton beams. This requires two-aperture magnets with fields in opposite directions. And because the LHC collides beams at higher energies, it requires larger magnetic fields.

In the process of upgrading the LHC and in conceiving future particle accelerators and detectors, the high-energy physics community is investing as never before in high-field magnet technologies. This creative process involves the United States, Europe, Japan and other Asian countries. The latest strategic plan for U.S. high-energy physics, the 2014 report by the Particle Physics Project Prioritization Panel, endorses continued U.S. leadership in superconducting magnet technology for future particle physics programs. The U.S. LHC Accelerator Research Program (LARP), which comprises four DOE national laboratories — Berkeley Lab, Brookhaven Lab, Fermilab and SLAC — plays a key role in this strategy.

The 15-year investment in Nb3Sn technology places the Fermilab team led by scientist Alexander Zlobin at the forefront of this effort. The Fermilab High-Field Magnet Group, in collaboration with U.S. LARP and CERN, built the first reproducible series in the world of single-aperture 10- to 12-Tesla accelerator-quality dipoles and quadrupoles made of Nb3Sn, establishing a strong foundation for the LHC luminosity upgrade at CERN.

The laboratory has consistently carried out in parallel an assertive superconductor R&D program as key to the magnet success. Coordination with industry and universities has been critical to improve the performance of the next generation of high-field accelerator magnets.

The next step is to develop 15-Tesla Nb3Sn accelerator magnets for a future very high-energy proton-proton collider. The use of high-temperature superconductors is also becoming a realistic prospect for generating even larger magnetic fields. An ultimate goal is to develop magnet technologies based on combining high- and low-temperature superconductors for accelerator magnets above 20 Tesla.

The robust and versatile infrastructure that was developed at Fermilab, together with the expertise acquired by the magnet scientists and engineers in design and analysis tools for superconducting materials and magnets, makes Fermilab an ideal setting to look to the future of high-field magnet research.

Emanuela Barzi

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This article first appeared in Fermilab Today on May 22.

Tengming Shen was awarded a DOE Early Career Award to develop a high-performance superconducting material for accelerator technology. <em>Photo: Reidar Hahn</em>

 

Over the years, engineers have found ways to cram more and more transistors onto a single integrated circuit. As a result of these improvements, they have been able to pack more computing power into smaller machines.

In much the same way, the key to developing better high-energy particle accelerators has been building increasingly powerful magnets to put inside them.

The Department of Energy recently presented an Early Career Research Award to Fermilab scientist Tengming Shen, a 2010 Peoples Fellow working to spur the next magnet revolution.

DOE awarded Shen $500,000 per year for five years for his research into engineering high-field superconducting materials for advanced accelerator technology. If his team succeeds, the work could pave the way for the construction of high-field superconducting magnets for future accelerators such as Fermilab’s proposed muon collider, for energy upgrades of the Large Hadron Collider and for the development of new medical imaging devices.

Shen’s strategy is to search for a better magnet-making material. Scientists currently use two niobium-based materials, NbTi and Nb3Sn.

“You have to go into a territory that’s new,” he said.

Shen works with superconducting magnets, which conduct electricity without resistance when cooled below a certain temperature. This reduces the amount of energy required to power them and allows them to achieve higher magnetic fields.

To reach this point in his research, Shen has collaborated with other scientists in the Very High Field Superconducting Magnet Collaboration, a partnership among U.S. national laboratories, universities and members of superconductor industry.

Fermilab’s Tevatron was the first particle accelerator to use niobium-titanium superconducting magnets. Before superconducting magnets, scientists had used iron or copper magnets, which required large amounts of electricity and, when used with insufficient cooling, tended to melt.

Fermilab founder Bob Wilson purchased as much niobium-titanium as he could, and Fermilab scientists developed a process for building large superconducting magnets. Members of industry eventually adopted the technology to mass-produce magnets used in MRI machines, now found in most hospitals. The major particle accelerators that have followed – the LHC at CERN, HERA at DESY and RHIC at Brookhaven National Laboratory – all depend on this technology.

Scientists cooled magnets in the Tevatron with liquid helium to 4.2 Kelvin; they reached a magnetic field strength of 4.3 Tesla. The scientists who built the Large Hadron Collider cooled their magnets with superfluid liquid helium to an even colder 1.9 Kelvin and almost doubled that performance to 8.3 Tesla. Fermilab and other U.S. laboratories have recently developed new technology using niobium-tin, Nb3Sn, which scientists hope will help them make the jump to 12- to 13-Tesla magnets.

The next step, according to Shen, is to push the limit of superconducting magnet technology by exploring new materials beyond the niobium family. This would allow scientists to more than double the energy reach of the LHC without increasing the size of the accelerator, he said.

Shen plans to study a group of high-field superconductors, in particular Bi2Sr2CaCu2Ox. He expects he could use this material to build magnets with a reach of up to 50 Tesla.

Even better, the new material could be used to construct 1- to 5-Tesla magnets that operate at higher temperatures. Whereas current superconducting magnets must be cooled with liquid helium, Shen’s magnets could potentially be cooled with a simpler refrigeration unit.

“Helium is very expensive,” Shen said. “There are many places like Africa, India and China that would like to develop cryogen-free devices.”

The development of high-temperature superconductors could eventually lead to better power lines, faster computers and more energy-efficient transportation, Shen said.

“There are many superconducting materials and many more to be discovered,” he said. “The whole world could be superconducting.”

—Kathryn Grim

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