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10 Oct 2023
Excimer lasers typically employed in displays production can also be used to make superconducting tape for magnetic-confinement reactors.
Excimer lasers from Coherent could be set for much wider use in fusion reactor applications, after the US-headquartered photonics giant signed a “letter of intent” with Japan’s Faraday 1867 Holdings.
Kanagawa-headquartered Faraday 1867 is said to be the world’s leading manufacturer of high-temperature superconducting (HTS) tape, via its subsidiary Faraday Factory Japan.
The tape is used in strong electromagnets that are used to confine plasma in magnetic-confinement fusion reactors.
According to the UK fusion startup Tokamak Energy, magnetic fields are used in the tokamak to confine and control the electrically charged plasma that constitutes the fusion reactor’s “fuel”.
These strong fields allow the plasma to be heated to a temperature above 100 million degrees Celsius - the threshold required for fusion to be a commercially viable energy source - and powerful magnets in spherical tokamaks enable more compact confinement, increasing plasma density and power while eliminating the need for expensive cooling with liquid helium.
The magnetic fields are generated by passing large electrical currents around arrays of electromagnet coils that circle the plasma, and those magnets are wound from what Tokamak Energy calls “groundbreaking” HTS tapes.
Functional coatings
Faraday Factory has been producing HTS tapes since 2012, and Coherent says that demand for the tape is expected to increase by a factor of ten between now and 2027.
Several manufacturing steps are needed to make the tape, with the Japanese firm using ion beam assisted deposition (IBAD), pulsed laser deposition (PLD), silver magnetron sputtering, and copper electrochemical plating.
“PLD is an extremely powerful tool to grow high-quality functional coatings,” says Faraday Factory on its web site. “The deposition process takes place from a plume produced by a laser beam hitting the target on metal tape with buffer layers at elevated temperature.
“[The] HTS compound is a complex oxide material; the PLD method plays an important role in producing [an] HTS layer with [a] strictly controlled composition, thickness, and microstructure."
The letter of intent it has signed with Coherent is said to outline a strategy to increase HTS manufacturing capacity with the firm’s “LEAP” lasers.
“Coherent LEAP excimer lasers are the industry standard in PLD that enable the manufacturing of HTS tape,” Coherent stated. Based around argon fluoride (ArF), krypton fluoride (KrF), and xenon chloride (XeCl) sources emitting at 193 nm, 248 nm, and 308 nm, the LEAP lasers are available with output powers of up to 300 W.
They are already used in a range of industrial applications, for example in laser lift-off stages for organic LED and microLED display production.
Fusion and beyond
Kai Schmidt, senior VP of Coherent’s excimer laser business unit, commented: “We understand that countries in the nuclear fusion energy race are looking to ramp up sustainable supply chains of HTS tape on the order of thousands of kilometers per year to keep fusion technology development on a fast track.
“We have been partners with Faraday 1867 for more than ten years, and we are eager to supply the lasers that will support the production ramp-up phase of HTS tape.”
Sergey Lee, representative director at Faraday Factory Japan, added: “Applications for HTS tape go beyond fusion reactors: they include loss-less energy transmission, zero-carbon aviation and container ships, helium-free MRI systems, advanced propulsion for spaceships, and many more.
“Combined, these applications are driving the double-digit annual percentage growth of the market for HTS tape, which is increasing the urgency to invest in HTS tape manufacturing capacity.”
• In a further tie-up with Japanese companies, Coherent has agreed a deal that will see it receive $500 million each from the electronics giants Mitsubishi Electric and Denso, in exchange for a share in its silicon carbide (SiC) wafer business.
The $1 billion deal will result in the two Japanese firms each taking a 12.5 per cent stake in a new subsidiary company, while Coherent retains a controlling 75 per cent share.
The development follows a strategic review of the SiC business initiated earlier this year, and although it does not impact Coherent’s photonics-related operations directly, it should enable the parent company to focus almost entirely on its lasers, optics, and photonics efforts.
Demand for SiC-based, wide-bandgap power electronic devices is expected to grow exponentially with the shift to all-electric vehicles and power transmission, and Coherent has long been a key supplier of the basic SiC materials from which individual semiconductor devices are fabricated.
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