USMDP an APS-DPB 2018 Highlight

Each year the America Physical Society Division of Physics of Beams newsletter asks leaders in the field to look back on the year’s the most important and timely topics. The 2018 edition focuses on US projects and programs, including the U.S. Magnet Development Program. More…

HL-LHC AUP Magnets Lauded at Fermilab Director’s Review

The US HL-LHC Accelerator Upgrade Project (AUP) underwent a Fermilab Director’s Review in July 2018. The committee was “very impressed with the report of magnet manufacturing progress.” More…

Magnet Diagnostics with a Thirst for a Quench

The Superconducting Magnet Program within ATAP, which participates in the multi-lab US Magnet Development Program, has been leading the way in developing novel quench diagnostics and bringing the existing ones to a new level of performance.More…

Delivery of Berkeley Lab ECR Magnet to FRIB Brings Future of Nuclear Science One Step Closer

The Berkeley Center for Magnet Technology has designed, built, and now delivered a key component of the ECR source for the Facility for Rare Isotope Beams: an advanced superconducting magnet configured to produce a sextupole field embedded within three solenoids. More…

LCLS-II Undulators Move Through Production

Another pair of soft-X-ray undulators (SXRs) arrived at SLAC in September 2017, making a total of six units delivered from vendors. The HGVPUs are moving through the production process as well. More…

DELIVERY OF BERKELEY LAB ECR MAGNET TO FRIB BRINGS FUTURE OF NUCLEAR SCIENCE ONE STEP CLOSER

At one of the flagship facilities being constructed by the DOE Office of Nuclear Physics — the Facility for Rare Isotope Beams (FRIB) at Michigan State University — everything begins with a high-performance source of heavy ions, the electron cyclotron resonance (ECR) source. The Berkeley Center for Magnet Technology has designed, built, and now delivered, a key component of the ECR source: an advanced superconducting magnet configured to produce a sextupole field embedded within three solenoids. More…

RECORD PERFORMANCE IN A HIGH-TEMPERATURE SUPERCONDUCTING MAGNET

The ATAP-led US Magnet Development Program (MDP) has set a current-density record for accelerator-style magnets made from high-temperature superconductor (HTS). The 3.3-tesla magnetic field quadrupled the HTS performance achievable just two years ago and was half again what could be achieved earlier this year.

Using a coil fabricated this summer by ATAP’s superconducting magnet program, the researchers built and tested a magnet made from Bi-2212 wire. The “racetrack” coil, made of 17-strand “Rutherford-style” cable, carried a record 8.2 kA while generating a peak field of 3.3 T, quadrupling performance of a dozen coils made before 2015 and representing a 60% increase over two coils made and tested in 2016 and earlier in 2017. The overall quench current density in the cable was 730 A/mm² and the wire’s engineering current density was 930 A/mm², which are practical current densities for applications.

Realizing the promise of HTS

High-temperature superconductor, whether used as inserts to augment traditional superconductors or (as in this case) as the principal conductor, has long offered tantalizing prospects to the developers of magnets for high-energy physics and other uses. The attraction is not their ability to superconduct at relatively high (though still cryogenic) temperatures—in fact, the work is done at the usual liquid-helium temperatures—but their high-field potential.

Increasing the field of an electromagnet calls for more current, but the wire and cable can only handle so much and remain superconductive. Traditional conductors, such as niobium-titanium (NbTi) and the higher-field niobium-three-tin (Nb₃Sn) materials that are now coming into use, have a critical current density that decreases rapidly as magnetic field increases. The critical current density of Bi-2212 decreases much more slowly as the field goes up. The engineering current density of this coil is expected to remain above 500 A/mm² even at 20 T — far above the magnetic fields achieved thus far in accelerator-style magnets.

		Thanks to a multi-institutional, public/private sector team effort at all levels from materials through wire and cable fabrication, racetrack coil RC-05 achieved critical current an order of magnitude greater than its predecessors of several years ago and half again that of its immediate predecessors in the current effort.

This high critical current density, together with new magnet designs such as the canted cosine theta technology also being explored by MDP, makes it possible to envision 20-T-class accelerator magnets for future high-energy colliders, such as an energy upgrade of the Large Hadron Collider or the notional Future Circular Collider. “This is great news not only for high-energy physics, but for spinoff applications throughout science, wherever high-field magnets are needed,” said ATAP Division Director Wim Leemans. Examples include 25 T solenoids for >1 GHz nuclear magnetic resonance (NMR) magnets.

Potential long-term implications are numerous. “Our interests include expanding all the frontiers of what’s possible,” Leemans adds, “including the cost-effectiveness and feasibility frontiers as well as absolute performance. “One of our overarching interests is bringing the accelerator to the application, and higher fields can mean smaller machines as well as new capabilities.”

According to Prof. David Larbalestier, Chief Materials Scientist of the National High Magnetic Field Laboratory (NHMFL) at Florida State University and Director of its Applied Superconductivity Center, “The parameters and performance of this coil and solenoidal coils made at NHMFL show that Bi-2212 is now a high-field conductor, ready for magnets that can enable superconducting magnet applications impossible with any other superconductor.” Looking beyond high-energy physics, NHFML has an application interest of its own in mind: developing 1.3-1.6 GHz NMR magnets using this round, multifilamentary, twisted, fine filament and macroscopically isotropic wire.

Click for larger version		Engineering a top-performing superconducting magnet requires mastery of seemingly fractal detail, from the overall design down to the formulation of materials. Superconducting material (powdered, in this case) is made into filaments, which are formed into wire, which is then woven tightly into a flat cable.

Partnering is key to the field

The record-setting magnet was the work of many hands. Dr. Soren Prestemon, head of ATAP’s superconducting magnet program and Director of the U.S. Magnet Development Program and the Berkeley Center for Magnet Technology, described it as “an example of what is possible when U.S. national lab, universities, and private industry come together to push technologies.”

The LBNL-fabricated coil coil was heat-treated at the NHMFL. The wire was made by Bruker OST LLC in New Jersey from a precursor Bi-2212 powder, which in turn had been manufactured by nGimat LLC in Kentucky using an innovative nanospray technology. Bruker OST LLC and nGimat LLC were supported by the U.S. Department of Energy’s Small Business Innovation Research (SBIR) program, working closely with the teams at LBNL and NHMFL, under the framework of the MDP.

“I’m extremely grateful for the dedicated and talented teams at LBNL, NHMFL, Bruker OST, and nGimat,” said Dr. Tengming Shen, the ATAP researcher who led the effort. The record-setting achievement is a culmination of his Early Career Research Program (ECRP) work, which began in 2012.

BERKELEY LAB MAGNET HELP MEANS PROGRESS TOWARD LHC LUMINOSITY UPGRADE

Excerpted from the Accelerator Technology and Applied Physics Division Newsletter and an article in Symmetry Magazine

The Berkeley Center for Magnet Technology (BCMT), along with colleagues at Fermilab and Brookhaven National Laboratory as well as CERN, is in the midst of a successful series of tests of a fundamentally new and far more powerful focusing quadrupole that will be key to the upcoming luminosity upgrade of CERN’s Large Hadron Collider. Both this advanced technology and the multi-lab and international collaboration model will doubtless be among many BCMT and ATAP contributions to Hilumi-LHC and whatever is beyond it in circular colliders for high-energy physics.

History and Context

Major accelerators tend to be repeatedly upgraded over the years, maximizing the scientific return on the investment. Before the LHC was even completed in its present version (famed as the discovery site of the Higgs boson), scientists and engineers were planning upgrades. LBNL has had a primary role since the inception of the four-laboratory US Large Hadron Collider Accelerator Research Program (US-LARP) collaboration that helps design and build components for these upgrades.

The latest effort is aimed at an order-of-magnitude increase in beam luminosity. This translates into a similar increase in the rate of particle collisions and thus the detail with which LHC users can explore the Standard Model of Particles and Interactions and search for new physics within the LHC’s energy reach. Hilumi-LHC made its official transition at CERN from an R&D program to a construction project last year, and US-LARP is under review for Critical Decision Zero (statement of mission need), a key go-ahead as a Department of Energy project.

An important ingredient in that tenfold luminosity increase is a set of new, unprecedentedly powerful focusing quadrupoles that will be installed just upstream of the interaction points for final focus of the beams just before collision. These quadrupoles will double the luminosity all by themselves, a major contribution to the factor-of-10 overall luminosity upgrade.

“We’re dealing with a new technology that can achieve far beyond what was possible when the LHC was first constructed,” says Giorgio Apollinari, Fermilab scientist and Director of US LARP, in a recent article in the Fermilab/SLAC magazine Symmetry. “This new magnet technology will make the HL-LHC project possible and empower physicists to think about future applications of this technology in the field of accelerators.”

This will represent the first major use of the high-field niobium-tin (Nb₃Sn, pronounced “niobium-three-tin”) superconductor in an operating accelerator. The version of the LHC presently operating, like other major colliders, uses the older niobium-titanium (NbTi) superconductor. The technology developed by LARP over the last decade will allow these magnets to achieve higher fields in significantly larger apertures, and will provide greater temperature margin, compared to the present interaction-region quadrupoles.

The new conductor called for innovative magnet designs. In contrast to the ductile NbTi cable, Nb₃Sn is embrittled by the heat treatment that is needed to render it superconducting. It has to be wound into finished coils before the heat treatment, requiring an entirely new approach to constructing the magnet.

“Niobium-three tin is much more complicated to work with than niobium titanium,” Peter Wanderer, head of the Superconducting Magnet Division at Brookhaven National Lab, told Symmetry. “It doesn’t become a superconductor until it is baked at 650 degrees Celsius. This heat-treatment changes the material’s atomic structure and it becomes almost as brittle as ceramic.”

LBNL played vital early leadership roles in the development of Nb₃Sn magnet technology, making it seem reasonable that this challenging new material could be the stuff of practical accelerator magnets. It took scientists and engineers here, along with other LARP collaborators, 10 years to devise and perfect the process to wind, form, bake and stabilize these coils.

Success with a New Model Magnet — And Model for Co-Operation

For these quadrupoles, BCMT, a joint venture of ATAP and the Engineering Division, has primarily been involved in cabling (weaving cables out of the strands of multifilamentary superconducting wire), structural design and analysis, and assembly of the final magnet prior to testing at Fermilab. Brookhaven and Fermilab are both going to wind, react, and pot the coils, and Brookhaven will also perform testing.

The magnet being tested, designated MQXFS1, is a so-called “model” quadrupole because it is at scale (1.5 rather than 4 m) in length, but it is full scale — in fact, of the final design — in all other aspects. (This use of magnets that are scaled down in length but otherwise full-sized is an established time and money saver. Most of the challenges occur at or near the ends or are brought about by an increase in the bore diameter.)

Achieving such success with the very first prototype required not only use of a novel superconductor and a magnet design that could take advantage of it, but also the right scheme for international cooperation and management. “US LARP is a unique collaboration where expertise in all areas of the magnet technology is shared among the participating laboratories, resulting in a very tightly interwoven team,” says Soren Prestemon of LBNL’s Berkeley Center for Magnet Technology.

The interwoven team approach has been extended to include the CERN HiLumi magnet team in the design, fabrication, and test of this first prototype, Prestemon explains, adding that “it bodes well for the future HiLumi project,” as both the US and CERN will be contributing magnets for the LHC luminosity upgrade. “Building this magnet prototype was truly an international effort,” adds Lucio Rossi, the head of the HiLumi project at CERN. “Half the magnetic coils inside the prototype will be produced at CERN, and half at laboratories in the United States.”

The result is shaping up as both a technology knowledge base and a collaboration model that will serve well not only HiLumi-LHC, but also circular colliders of even higher energy. Though many years in the future, such colliders are already the subject of lively discussion in the high-energy physics community, which even as it makes use of the present state of the art,has always focused on what can be achieved next.

To Learn More…

“Physicists Build Ultra-Powerful Accelerator Magnet,” Symmetry Magazine, April 7.
“HiLumi-LHC Project Transitions from Design Study to Machine Construction Phase,” ATAP News, November 2015.
High Luminosity LHC Project website.
US LHC Accelerator Research Program website.