Taking on the toughest problems is the way to learn the most
Ever-stronger magnets (which must be cost-effective as well) are a key to building tomorrow’s high-energy accelerators and upgrading today’s. Our role — as not only a leading R&D group but also the administrators of Department of Energy’s multi-institutional National Conductor Development Program — is to create both evolutionary improvements and paradigm shifts in the design and application of accelerator magnets, providing innovative technology that enables new science and spinoff applications.
Our program has vertically integrated expertise “from melt to magnet” — that is, from basic material science, through making cable and designing, building, and testing magnets — and we have achieved an unparalleled level of integration of design and simulation tools. These efforts are extensively collaborative with colleagues elsewhere and with industrial partners, as a coordinated part of overall Department of Energy programs. Our always close cooperation with LBNL’s Engineering Division has recently become part of the Berkeley Center for Magnet Technology.
The Base Program: A Common Foundation for Many Areas of Progress
The performance requirements of modern accelerators continue to press the limits of magnet technology. Besides R&D that is strongly focused on magnets for a particular project, we have a base program that performs research of long-term or general benefit. (The “base program” is not a specific single line item in a budget or box on an organization chart. We use it as a portmanteau term for those efforts that are of generic benefit to all, rather than parts designed for a specific accelerator.)
Our philosophy is high-risk but high-potential-payoff R&D that expands the limits of superconducting magnet technology, a high-leverage investment that can benefit a wide variety of applications.
The limit for superconducting magnets of this size and shape used to be about 10 tesla. We have attained 16 T and are studying ways of reaching 20 T. This would have been an absurd number for accelerator-type magnets just a few years ago, but we have come to regard it as achievable.
The implications of such high-field magnets go beyond our principal role in high-energy physics. Other applications that could benefit — perhaps to a transformative degree — include magnetic resonance imaging; insertion devices for synchrotron-light sources and free electron lasers; and smaller, cheaper “gantries” that guide the proton or heavy-ion beam of a therapy accelerator to the patient.
While working to advance the state of the art in superconducting material, forming it into cable, and designing and building magnets, we emphasize cost-effective approaches to conductor and magnet fabrication techniques.
Much of our effort now focuses on a novel magnet geometry that is called “canted cosine-theta” because of the geometry of the windings (for dipoles) and that, in some cases, holds the superconducting cable in a channel. The goal is to manage stress under high magnetic fields. Stress management has the goal of minimizing the “training” process in which a new magnet is progressively broken in before it reaches its full capability. Training, in turn, reduces the likelihood of “quenches” in which part of the magnet becomes normal-conducting, forcing its stored energy (and the beam) to be dumped and the accelerator to be restarted. It is also simpler in many ways to manufacture, compared to earlier accelerator-style superconducting magnets, and gives excellent geometric field quality. We are now aggressively pursuing a practical demonstration of this promising concept.
DOE Conductor Development Program: Improving the Most Fundamental Part of Future Magnets
The goal of this ongoing program, now in its 14th year, is to provide cost-effective, high-performance superconductors for the high-field magnets required for the next generation high-energy physics (HEP) colliders. It is an industry-based national program which we manage on behalf of the DOE Office of High Energy Physics. Target specifications for conductor were developed in collaboration with the major U.S. HEP laboratories and university groups engaged in high-field superconductor development.
Its first phase is primarily R&D leading to an improved understanding of the factors that influence conductor performance and cost. The main goal of the R&D work is to improve our understanding of the key parameters that control the properties of Nb3Sn. Using on the knowledge gained from this research as a base, the program will (contingent on agency priorities and funding) enter a fabrication scale-up phase where the performance and cost-effectiveness can be demonstrated on production-size quantities. We expect this program to expand in scope in future years to include more processes and perhaps more participants, depending on the experience in the early years.
Even though Nb3Sn is going to be the principal material used in the next generation of high-field magnets, CDP must look 10 to 20 years into the future for superconductors that might be used beyond the limits of Nb3Sn. Therefore it also offers some funding for the development of Bi-2212 round wire (a high-Tc material) that can be used for dipole magnets at 20 T and above, and solenoids above 30 T.
LARP: The Next Chapter in the Story of the LHC
Accelerators are not just built — they are repeatedly rebuilt over the years, maximizing the scientific return on the investment. The Large Hadron Collider at CERN is no exception. Before it was even completed in its present version (famed as the discovery site of the Higgs boson), scientists and engineers were planning upgrades. This effort came to be called LARP, the Large Hadron Collider Accelerator Research Program. A major part of it was US-LARP (the LHC represents an unprecedented level of partnership between the collective US accelerator community and onetime collegial archrival CERN). LBNL, prominently including the Superconducting Magnet Program, has had a primary role since the inception of the four-laboratory US-LARP collaboration.
One of the major upgrades envisioned for the LHC was a tenfold increase in its beam luminosity (the concentration of particles heading straight toward their oncoming counterparts at the interaction point). Since the 2013 approval by CERN of High-Luminosity LHC, we have been transitioning our LARP effort from a set of R&D programs to a project.
The Superconducting Magnet Program’s primary role in LARP is the development of high-performance interaction-region quadrupoles based on Nb3Sn conductor. (This will be the first major use of Nb3Sn in an operating accelerator.) The IR quadrupoles are among the keys to higher luminosity, as their function is final focusing of the beams destined for collision. The new ones will by themselves double the luminosity. The technology developed by LARP over the last decade will allow these magnets to achieve higher fields in significantly larger aperture then the current ones, and to provide greater temperature margin than would be possible with the NbTi superconductor of the present IR quadrupoles.
As the magnet R&D phase approaches completion, the focus of the LARP magnet program turns toward reducing the construction project risk by developing the design and demonstrating the performance of the new IR quadrupoles, as well as ensuring compatibility of the final focus system with the other improvements that add up to the order-of-magnitude improvement to integrated luminosity.
Besides superconducting magnets, other ATAP and LBNL contributions to LARP have included accelerator physics studies, as well as design, fabrication and commissioning of critical accelerator instrumentation. Crab cavities (radiofrequency devices that slip the otherwise separately orbiting beams onto a head-on collision course) and high-bandwidth feedback systems for optimization of the upgraded interaction regions, are among the efforts that will involve us. Accelerator physics studies and modeling, especially with regard to beam-beam effects, will also be prominent.
Looking further into the future, there might be an energy upgrade of the LHC, which would also place great demands on the world’s collective expertise regarding superconducting materials and magnets.
A Commitment to Partnering and Innovation
The physical scope of today’s major accelerators mandates extensive commercial participation and takes good advantage of concentrations of specialized expertise in the private sector. In the early 1990s, the Superconducting Super Collider Magnet Industrialization Program, a technology-transfer success of behalf of a collider that was fated not to be built, helped industrial partners learn to mass-produce accelerator-style magnets of the requisite quality. More recently, the DOE National Conductor Development program has systematized our ongoing, interactive collaboration with the companies that make superconducting materials and form them into wire and cable. It complements the Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) programs, in which we have often been asked to provide solicitation input and proposal review.
Oxford Superconducting Technologies, as well as Luvata, are among the companies we are presently working with in the Conductor Development Program because of their large-scale production experience in making superconductor. Supramagnetics, Showa Cable Systems, and ATI Wah Chang are just a few of our other collaborators over the years.
This optimization of private-sector capabilities has potential societal benefits far beyond high-energy physics; advanced magnetic-resonance imaging, cancer-therapy accelerators, and superconducting magnetic energy storage are among the possible spinoff applications of better superconductors and magnets. We welcome inquiries from prospective R&D collaborators as well as designers of systems that might benefit from advanced superconducting magnets. See the “Working With Us” tab at the top of this page, or contact Division Deputy for Technology Soren Prestemon.
In general, the corresponding or principal author is listed first. Indicating the broad collaborative nature of our work, some entries (noted in italics) have a corresponding author outside LBNL.