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Flux Staff Report

Talk about an upgrade: Engineers and technicians at the Magnet Lab are now the sole holders of the record for the world's strongest "resistive" magnet — a type of electromagnet that uses electricity to generate high magnetic fields.

The team bested its previous record to produce a resistive magnet with a field of 36 tesla, squeaking by the 35-tesla record the lab briefly shared with the Grenoble High Field Laboratory in France.

A model of the new 36-tesla insert.
Click for larger image.

Rather than building a pricey new magnet, the team reengineered one of the lab's existing 35-tesla magnets. Higher field usually requires higher power, but this upgrade resulted greater research power for the lab's users without an increase in the electric bill. More on how they did it in a minute.

First, you need to understand that engineers at the Magnet Lab never stop fine-tuning, tinkering and rethinking their magnet designs. This explains why the laboratory holds numerous records – 13 at last count – for strength of field and other key measures of high-magnetic-field research.

Resistive magnets are designed and assembled in-house using so-called Florida Bitter technology pioneered at the Mag Lab. 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.

Engineers don't like being stuck, and limits exist to be worked around. So Magnet Lab engineers adjusted the stacking pattern of the bitter plates, and in so doing found 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.

The 36-tesla magnet, which has a 32-millimeter (1.25-inch) experimental space, will be used primarily for physics and materials science research.

Jingping Chen, manager of the resistive magnet program at the Magnet Lab, said the upgrade of the magnet is just a start. Using the new stacking pattern, major upgrades are planned for many of the resistive magnets at the laboratory, starting with the lab's other 35-tesla magnet.