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Researchers Use New Approach To Overcome Key Hurdle For Next-Generation Superconductors

Researchers from North Carolina State University have developed a new computational approach to improve the utility of superconductive materials for specific design applications – and have used the approach to solve a key research obstacle for the next-generation superconductor material yttrium barium copper oxide (YBCO).

A superconductor is a material that can carry electricity without any loss – none of the energy is dissipated as heat, for example. Superconductive materials are currently used in medical MRI technology, and are expected to play a prominent role in emerging power technologies, such as energy storage or high-efficiency wind turbines.

One problem facing systems engineers who want to design technologies that use superconductive materials is that they are required to design products based on the properties of existing materials. But NC State researchers are proposing an approach that would allow product designers to interact directly with the industry that creates superconductive materials – such as wires – to create superconductors that more precisely match the needs of the finished product.

“We are introducing the idea that wire manufacturers work with systems engineers earlier in the process, utilizing computer models to create better materials more quickly,” says Dr. Justin Schwartz, lead author of a paper on the process and Kobe Steel Distinguished Professor and head of NC State’s Department of Materials Science and Engineering. “This approach moves us closer to the ideal of having materials engineering become part of the product design process.”

This snapshot of 3-D temperature distribution within YBCO tape during a quench illustrates that the temperature gradient can be very high locally, thus requiring the multiscale modeling approach Schwartz's team developed.

To demonstrate the utility of the process, researchers tackled a problem facing next-generation YBCO superconductors. YBCO conductors are promising because they are very strong and have a high superconducting current density – meaning they can handle a large amount of electricity. But there are obstacles to their widespread use.

One of these key obstacles is how to handle “quench.” Quench is when a superconductor suddenly loses its superconductivity. Superconductors are used to store large amounts of electricity in a magnetic field – but a quench unleashes all of that stored energy. If the energy isn’t managed properly, it will destroy the system – which can be extremely expensive. “Basically, the better a material is as a superconductor, the more electricity it can handle, so it has a higher energy density, and that makes quench protection more important, because the material may release more energy when quenched,” Schwartz says.

To address the problem, researchers explored seven different variables to determine how best to design YBCO conductors in order to optimize performance and minimize quench risk. For example, does increasing the thickness of the YBCO increase or decrease quench risk? As it turns out, it actually decreases quench risk. A number of other variables come into play as well, but the new approach was effective in helping researchers identify meaningful ways of addressing quench risk.

“The insight we’ve gained into YBCO quench behavior, and our new process for designing better materials, will likely accelerate the use of YBCO in areas ranging from new power applications to medical technologies – or even the next iteration of particle accelerators,” Schwartz says.

“This process is of particular interest given the White House’s Materials Genome Initiative,” Schwartz says. “The focus of that initiative is to expedite the process that translates new discoveries in materials science into commercial products – and I think our process is an important step in that direction.”

The paper, “Three-Dimensional Micrometer-Scale Modeling of Quenching in High-Aspect-Ratio YBa2Cu3O7-d Coated Conductor Tapes—Part II: Influence of Geometric and Material Properties and Implications for Conductor Engineering and Magnet Design,” was co-authored by Dr. Wan Kan Chan, a research associate at NC State. The paper is available online from IEEE Transactions on Applied Superconductivity. The research was funded by the Air Force Research Laboratory.

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Note to Editors: The study abstract follows.

“Three-Dimensional Micrometer-Scale Modeling of Quenching in High-Aspect-Ratio YBa2Cu3O7-d Coated Conductor Tapes—Part II: Influence of Geometric and Material Properties and Implications for Conductor Engineering and Magnet Design”

Authors: Wan Kan Chan and Justin Schwartz, North Carolina State University

Published: online, IEEE Transactions on Applied Superconductivity

Abstract: YBa2Cu3O7-d (YBCO) coated conductors (CCs) show great promise for applications, but due to a very slow normal-zone propagation velocity (NZPV), quench detection and protection in YBCO magnets may be difficult. Present YBCO CCs have been developed with a primary focus on maximizing the critical current density for elevated-temperature low-field or low-temperature high-field applications. As the market for magnet applications progresses, it becomes important to consider design parameters such as the thicknesses and properties of all YBCO CC components, with the intent of considering quench-related behaviors as an integral part of the conductor and magnet design processes. Thus, it is important to know the impacts of conductor parameters on quench behavior. Considering that the YBCO layer itself is on the order of a micrometer in thickness, quench behavior must also be considered at this scale length. Here, the highly accurate experimentally validated micrometer-scale 3-D tape model reported in Part I is used to study how variations in CC geometry and material properties affect quench behavior, including the NZPV, hot-spot temperature, and minimum quench energy. The parametric variations focus on quantities that can be most readily modified by CC manufacturers. Based on simulation results, the relative sensitivities of the quench quantities to the parametric variations are calculated to identify which CC design parameters are most impactful on quench behavior. The implications of these results for quench detection and protection are discussed.

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