The American Association for the Advancement of Science (AAAS) publication Science reports on two young start-up companies, Commonwealth Fusion Systems, and Tokamak Energy of the U.K., which are working on building small, powerful magnets using high-temperature superconductors. The secret lies in a new technology which allows the “deposit of thin layers of superconducting rare-earth barium copper oxide (ReBCO) on metal tape.”
Large tokamaks, such as the International Thermonuclear Experimental Reactor, or ITER, that 35 nations are constructing in France, depend upon huge superconducting magnets to contain the plasma — ionized gas of hydrogen isotopes which can reach temperatures of more than 100 million degrees Celsius.
“At ITER, sufficiently powerful fields are achieved using niobium alloy superconducting wires that can carry huge currents without resistance through magnet coils. But such low-temperature superconductors must be chilled to 4° above absolute zero, which requires bulky and expensive liquid helium cooling. And there’s a limit to the amount of current the niobium wires can carry, forcing ITER to adopt huge magnets with many wire turns to generate the needed fields. ITER’s largest magnets are 24 meters across, contributing to the reactor’s $20 billion price tag.”
However, the ReBCO can operate at the “warmer” temperature of 77° Kelvin, and can also carry higher currents.
