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Defect-Tolerant High-Temperature Superconductor for Coil Applications


RT&L FOCUS AREA(S): General Warfighting Requirements

TECHNOLOGY AREA(S): Materials / Processes

OBJECTIVE: Develop advanced manufacturing techniques for a high-temperature superconductor that minimize the impact of defects during its fabrication with the goal to use it in high-temperature superconducting (HTS) magnet coil applications.

DESCRIPTION: The Navy has been developing HTS systems over the past few decades using HTS coils. The coils are made from HTS wire that has the ability to pass large electrical currents with essentially no voltage drop due to its zero resistance when below the transition temperature. Therefore, there is tremendous advantage to use HTS technology in applications that require generating magnetic fields such as large-bore magnets, high-field magnets, motors, generators, and superconducting magnetic energy storage (SMES) systems.

One risk to HTS-based magnet systems is the quench of the superconductor. A quench is when an HTS wire transitions from its superconducting state to its normal-conducting resistive state. Typically, the transition initiates in a local region referred to as “normal zone” that no longer has zero resistance, and behaves as a conventional conductor with joule heating. A quench is critical in a magnet-based system since magnets inherently store large amounts of inductive energy that will be converted to heat at the location of the quench. If the onset of a quench cannot be prevented the heating of the superconductor to an elevated temperature can cause irreversible and catastrophic damage to the magnet.

There has been research in the area of attempting to protect HTS coils by integrating a quench detection and protection system. Investigations have been performed in the past on criteria for quench detection that looked at the origin of a quench in an HTS wire. Most recently, there has been work on estimating the impact of fluctuations in the transport of current in HTS wires and its performance on superconducting devices. High-field HTS magnets have large electrical inductances that store mega-joules of energy. When a quench occurs, this energy converts to heat in the normal zone of the conductor and has the potential to cause a burnout in the HTS coil. Defects in the HTS conductor that manifest during the manufacturing process can go unnoticed and contribute as a weak point prone to quench initiation. Experiments and simulations have been completed to find limits of quench where the conductor may be operated stably and protected from damage by adding additional material to the conductor. When the conductor is used in a coil application, some alternate techniques are employed when winding a coil to better tolerate defects in the conductor, such as no-insulation wind approaches.

The Navy’s desire is for a defect tolerant HTS wire capable of continued operation through a partial quench enabling additional time for a quench detection system to react and protect the HTS magnet system. Therefore, proposed solutions must address the HTS wire itself, and NOT the method for winding HTS coils. This is imperative so the end product may be applicable to not only superconducting magnet coils as found in HTS motors, generators, or SMES systems, but eventually in power distribution cables.

The proposed solution to create defect tolerant HTS wire may be by either alternate wire manufacturing techniques, or by alternate HTS wire topologies. The solution must retain all aspects of conventional HTS wire and operate with a minimum engineering current density of 200 Amps/square millimeters [A/mm2] while at operating temperatures of 30-40 Kelvin [K] in a 1-3 Tesla [T] background field. The final form of the HTS must be compatible with lamination of alternate materials, (i.e., copper, brass, stainless steel) other than the substrates used during manufacturing to give the final wire structure suitable for winding a coil. It must also follow conventional laminated HTS wire dimensions and have a width between 4-12mm, and a thickness approximately 0.05-0.2mm to enable the use of conventional HTS wire insulating machines. The HTS wire solution must also be producible in lengths with a minimum of 300m. The final product will need to demonstrate the ability of the conductor to continue operation (through a partial quench) even if it has local defects, by introducing known defects to the proposed conductor and comparing against known defects in a traditional HTS wire.

PHASE I: Develop a concept for a defect tolerant HTS wire that addresses defect mitigations during fabrication, or for alternative HTS topologies to increase defect tolerance in the conductor that meets the objectives stated in the Description. Demonstrate the feasibility of the proposed concept through modeling, analysis, and concept demonstrations. Quantify the clear benefits in the alternative fabrication techniques or HTS wire topologies. Since no industry standards exist for verification of defect tolerant HTS conductor, develop a plan and method of testing to be performed in Phase II to ensure defects are mitigated or tolerated; and that includes the cost to implement changes to fabrication or HTS wire modification, and a schedule with milestones to implement changes. The Phase I Option, if exercised, will include the initial layout and capabilities description to fabricate HTS wire in Phase II.

PHASE II: Fabricate sample prototype length HTS wire with minimal defects based on the Phase I work and Phase II Statement of Work (SOW) for demonstration and characterization of key parameters of the conductor in the Description. Demonstrate manufacturing process defect tolerance through introduction of known defects to compare against known defects in a traditional HTS conductor. Execute plans for methods of testing identified in the Phase I effort to prove the full-scale metrics. Based on lessons learned through the conductor testing, develop a substantially complete design and stand-up of the manufacturing process for long length conductor fabrication. Ensure this design includes all ancillary equipment required for fabrication and a means for testing the final product. Final deliverables should include samples of the conductor to be tested by the U.S., either the Navy or an alternate facility identified by the Government.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Navy use. Although defect tolerant HTS conductor is initially targeted for use in HTS coils for large-bore magnets, acquisition programs utilizing HTS coils, either as a major system or as a sub-system, in larger programs such as motors or generators.

The desired defect tolerant HTS wire has applications in commercial large-bore superconducting magnets used in the medical field, or in large-particle accelerators, as well as, commercial wind generators, and fusion systems. The conductor may also be applied to superconducting power distribution, superconducting electric grids, or alternative energy technologies using superconducting systems.


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