Resistive magnets are built in-house at the magnet lab using so-called Florida Bitter technology pioneered by researchers there. Circular plates of copper sheet metal are stamped with cooling holes; insulators with the same pattern are placed between the plates and stacked to make a coil. Voltage is then run across the coil and current flows to make a magnetic field in the center. Because of the limits of available materials (both to conduct current and to minimize stress on the coils), engineers were stuck at 35 tesla for about four years.
But magnet lab engineers discovered that by adjusting the stacking pattern of the Bitter plates, they could increase the magnetic field without increasing stress on the coils. This cost-neutral modification means a higher magnetic field can be created using the same amount of power, 20 megawatts. By comparison, the magnet at the Grenoble High Magnetic Field Laboratory achieves its 35 tesla using 22.5 megawatts of power.
Jingping Chen, manager of the resistive magnet program at the magnet lab, said the upgrade of the magnet is just a start, and that major upgrades are planned for many of the resistive magnets at the laboratory.
“We believe this magnet has the potential to reach even higher fields,” Chen said. “We plan to upgrade our other 35-tesla magnet this year as well. And our wider-bore, 31-tesla magnets will be upgraded to around 33 tesla — which will be a new record in the 50-millimeter (1.97-inch) category.”