A magnet for a future atom smasher.

Scientists at the Lawrence Berkeley (Calif.) National Laboratory have constructed the most powerful dipole magnet in the world. Its field strength measures 13.5 teslas, or about 250,000 times stronger than Earth's magnetic field. A Dutch group set the previous record of 11.03 teslas in 1995.

Designed for use in high-energy particle accelerators, the magnet is about three times stronger than those at Fermilab's Tevatron collider in Batavia, Ill. (SN: 9/28/85, p. 202). "We hope that it will generate new designs for future machines," says Ronald M. Scanlan, a materials scientist at Lawrence Berkeley.

The magnet consists of 14 miles of superconducting wire wound into four coils. After the coils are assembled and sheathed in 18 layers of stainless steel, they form a, cylinder 1 meter long and 1 meter in diameter. Electricity passing through the wire creates the intense magnetic field.

Unlike other high-strength magnets, which use a flexible niobium-titanium alloy as the superconductor, this one uses brittle niobium-tin. The new material ultimately enhanced the finished magnet's performance, but it posed a significant challenge to production because the wire couldn't simply be wound around itself.

Scanlan and his colleagues solved this fabrication problem by coiling the more flexible component materials. "The final crystalline form is brittle, but the individual materials are quite ductile," Scanlan says. They wrapped copper wire containing filaments of niobium and droplets of tin into coils and then heated them to about 680 [degrees] C, melding the components to form the superconducting alloy To harden and strengthen the brittle coils, the scientists filled the voids with epoxy.

Next, the team plans to test other formulations of the niobium-tin alloy and to examine other superconductors, such as niobium-aluminum. Different materials could push the field strength higher or bring down the construction cost.

The new magnets probably won't find their way into a particle accelerator anytime soon. It's too late to include them in plans for the European Laboratory for Particle Physics' Large Hadron Collider, currently under construction in Geneva and scheduled for completion in 2004. In the meantime, researchers can use the magnet to study the effect of high fields on materials, Scanlan says.