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Meet the Magnets

The 900 MHz NMR Magnet

Vital Statistics
	Strength	21.1 tesla
	Type	Superconducting
	Bore size	105 mm (~4 inches)
	Online since	July 2004
	Cost	$16 million
	Weight	36,287 kg (40 tons)
	Height	4.7 meters (15 feet, 6 inches)
	Operating temperature	-271.45 ° C (-456.61 ° F)
	Length of superconducting cable	153 km (95 miles)

Overview

What makes this magnet particularly special is its bore size (the space in the middle where scientists place their experiments). At 105 millimeters (about 4 inches), it is as wide as an orange. That's more than three times larger than the bore of our 45 tesla hybrid magnet. While that might not sound like much, it is the largest in the world for this type of magnet, and makes it possible for scientists to study small living animals. That’s why this magnet is called the “ultra-wide bore” magnet. Other NMR/MRI magnets of comparable field have typical bore diameters of 54 mm (one system has a diameter of 89 mm). With a field strength of 21.1 tesla, this is the strongest MRI scanner in the world.

This magnet, designed and built by the lab’s Magnet Science & Technology department, is used for nuclear magnetic resonance research. The magnet is used both for imaging (as done with less sophisticated MRI scanners in hospitals) and for spectroscopy. As an imaging device, this magnet helps scientists look inside small living animals such as rodents, birds and insects, and helps researchers study TB, flu and neurodegenerative disease. Scientists are also using it to explore different contrast agents that could help improve MRIs. In addition to imaging for biological research, the magnet is used by chemists to determine the composition of solids (solid state NMR) and liquids (solution state NMR) with measuring devices called spectrometers.

The brain of a finch,
as seen with the 900 MHz.

Since it was first charged in July 2004, this instrument has been continually conducting 300 amps of electrical current by itself – through some 153 kilometers (95 miles) of superconducting cable. Because it is superconducting, the current runs without resistance, so no outside energy source is needed. However, large amounts of liquid helium, an extremely cold substance, are needed to keep the magnet at a superconducting temperature. The cryostat contains 2,400 liters (545 gallons) of liquid helium, which keeps the magnet at 1.7 Kelvin (a scientific measurement equivalent to -456.61 degrees Fahrenheit or -271.45 degrees Celsius).

Magnets used for NMR are often referred to by their frequency rather than their magnetic field strength. That’s why this is called the 900 MHz. The instrument does spectroscopy and imaging by identifying the hydrogen atoms in the sample. It identifies these atoms by targeting energy at them in the form of radio waves. These waves must be of a very specific frequency for the hydrogen atom to respond. For a 21.1 tesla magnet, that frequency – the resonant frequency of a hydrogen proton – is 900 MHz.

Overview

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