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Meet the Split Helix Magnet

Diagram of the split magnet. Diagram of the split magnet.

While the Magnet Lab has developed 14 previous world-record resistive magnets over the years, the new 25 tesla Split magnet is not simply the next in line. This world-unique magnet system required a complete rethinking of resistive magnet technology’s limits.

The Split magnet consists of five resistive coils, with the first two innermost coils electrically connected in parallel and three more outer coils electrically connected in series. To meet this magnet’s considerable design challenges, Split Florida-Helix technology is used around the mid-plane of the two inner most coils and state-of-the art Florida-Bitter technology (see graphic below) is used for the regular winding in all five coils. All the resistive magnets developed previously at the MagLab were solenoids; most used the Florida-Bitter technology developed at the Magnet Lab (now used by five of the six largest resistive magnet labs worldwide). However, relying solely on Florida-Bitter technology wasn’t an option; the most efficient part of any high-field solenoid is the mid-plane region, and in the 25 T Split, more than half the midplane region is missing to provide vacuum space for scattering. How do you build a magnet that everyone says is impossible? Slowly. Testing on the design for the magnet’s central coil began in 2007.

Vital Statistics
Strength 25 tesla
Type Split Resistive
Bore size 32 mm (~1.25 inches)
Port size 45° by 11.4°
Individual parts 18,236 (including 5,000 bitter plates)
Online since June 2011
Cost $2.5 million
Weight 5,778 kg (or 12,739 lbs - as much as a female African elephant)
Height 2.1 meters (7 feet)
Power required 28 MW (second only to the Hybrid)

The centerpiece of this magnet is a group of four elliptical scattering ports. The process of machining the space around these ports was so complicated that the lab was unable to find a commercial vendor who’d agree to do the job. We solved that problem by building the unbuildable parts in-house.

Inventing the Split Florida-Helix

When electricity is conducted through a metal coil, or helix, it creates a strong magnetic field. All of our electromagnets are built on this very simple idea.

The Split magnet primarily uses Florida-Bitter plates to create helixes. We stacked thousands of these plates inside the Split. Then we nestled several stacks (like a Russian doll) to increase magnetic field strength.

We couldn’t use bitter plates in the places where the access ports poked through, so our scientists & engineers specially invented the Split Florida-helix to accommodate the four ports going through the middle of the Split.

Research Capabilities: Optics & More

The 25 T Split magnet enables never-before-possible optics experiments. What’s so special about optics experimentation? Scientists learn more about the intrinsic properties of materials by shining light on them. Looking at which kinds of light are absorbed or reflected at different angles gives researchers insight into the fundamental electronic structure of matter, and that’s the kind of stuff that over decades has led to smaller and faster computers, and other quality-of-life enhancements.

In addition to optics experiments, this magnet is also useful for Fourier transform infrared resonance, electron magnetic resonance, and x-ray experiments. To keep the magnet as responsive as possible to different experimental approaches, the entire magnet can rotate 90 degrees, making the magnetic field parallel to the floor.

Video: The Making of the Split Helix Magnet

Image Gallery

View this photo set on Flickr

Last modified on 21 May 2018

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