S. Korea develops world's first inspection system for superconducting wire accurate to fraction of a hair's width

South Korean researchers have developed what they say is the world's first ultra-precision inspection technology capable of detecting microscopic flaws in superconducting wire before they cause catastrophic damage or performance loss in superconducting magnets used in nuclear fusion devices and MRI machines.

The system can detect thickness variations as small as a fraction of one-hundredth the width of a human hair — without cutting or touching the wire, even when it stretches hundreds of meters long.

The Korea Electrotechnology Research Institute (KERI) announced Sunday that a research team led by Ha Hong-su and Park In-sung of its Cryogenic Device Research Center had developed the world's first three-dimensional ultra-precision inspection system capable of continuously measuring the thickness and width of high-temperature superconducting wire without contact. The wire comes in tape form thinner than a sheet of paper and can run hundreds of meters in length.

High-temperature superconducting wire is a material whose electrical resistance drops to zero below a certain temperature, allowing large currents to flow without loss. It is a core component of the powerful superconducting magnets used in nuclear fusion devices, medical MRI machines and high-efficiency power equipment.

The wire takes the form of a long tape just tens of micrometers thick — thinner than a sheet of A4 paper — and 4 to 12 millimeters wide. Superconducting magnets are built by winding hundreds of layers of this wire tightly together.

The problem lies in thickness variations of just a few micrometers in a single strand of wire. Even minute discrepancies, once stacked hundreds of layers deep, can cause significant deformation in the overall size and shape of a magnet. Stress can concentrate in specific areas, causing the magnet to fracture or the magnetic field to become unstable, sharply degrading equipment performance.

Existing contact-based inspection methods risked scratching or contaminating the wire surface, while non-contact approaches lost measurement accuracy when the wire vibrated during transport. Precise inspection also required cutting the expensive wire and examining its cross-section under a microscope.

To overcome these limitations, the research team combined a reel-to-reel transport mechanism — which winds wire from one reel to another — with vertically opposed chromatic confocal laser sensors.

Two laser sensors mounted above and below the wire rapidly scan its surface from side to side, simultaneously measuring the distance to both surfaces. The confocal laser method allows stable measurement even on highly reflective metal surfaces such as silver or copper.

The system keeps measurement error within ±1.5 micrometers even when the wire moves and vibrates at 100 meters per hour. When the sensor's lateral movement is precisely controlled to 4 millimeters per second or less, the repeated measurement error drops to 0.2 micrometers or below.

This allows the full length of hundreds of meters of wire to be inspected continuously without cutting, providing a real-time three-dimensional picture of where the wire is thinner or thicker, and whether its cross-section is convex or concave.

Beyond high-temperature superconducting wire, the technology can be applied to quality inspection of other advanced materials produced in long, continuous runs — including copper and aluminum foil for secondary batteries, rolled metal products, thin-film solar cells and precision films for electronic components.

The team plans to develop the technology further into a smart quality-control system that links measurement data in real time with production equipment, automatically adjusting plating and rolling process conditions.

"Microscopic thickness variations in high-temperature superconducting wire are invisible to the naked eye, but when stacked hundreds of layers deep they can determine the performance and reliability of an entire superconducting magnet," Ha said. "This will serve as a starting point for smart manufacturing technology that detects invisible micro-errors early in the production stage and manages the quality of advanced materials autonomously."