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News & Media

Latest ITER Newsline

  • Question of the week | Will fusion run out of fuel?

    One of the paradoxes of fusion, the virtually inexhaustible energy of the future, is that it relies on an element that does not exist—or just barely. Tritium, o [...]

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  • Managing data | Setting up a robust process

    Are the ITER systems and processes robust enough to manage the technical and project data for a program of ITER's complexity? Will quality information be made a [...]

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  • Image of the week | Bullseye

    Two perfectly circular structures, looking a lot like archery targets, have been installed on the west-facing wall of the Tokamak Complex. They are not for sh [...]

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  • Art and science | Seeking new perspectives on fusion

    Standing in the middle of the Tokamak Building, sound artist Julian Weaver positions his 3D microphone near one of the openings of the bioshield to record the s [...]

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  • Worksite photos | The view one never tires of

    For the past three-and a half years, ITER Communication has been documenting construction progress from the top of the tallest crane on the ITER worksite. Altho [...]

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Of Interest

See archived entries

Naive question of the week

What happens to the car keys?

We begin today a new series that aims to answer basic, even naive, questions about fusion and ITER.

An image used often, when trying to convey the amount of energy stored into the ITER central solenoid, is that of a magnet lifting an aircraft carrier out of the water.

The ITER central solenoid is one of the most massive (1,000 tonnes) and powerful magnets ever manufactured. It could lift an aircraft carrier from the water. But could it also snatch the car keys from the pocket of an operator standing in the Diagnostics Building, some 30 metres distant? (Click to view larger version...)
The ITER central solenoid is one of the most massive (1,000 tonnes) and powerful magnets ever manufactured. It could lift an aircraft carrier from the water. But could it also snatch the car keys from the pocket of an operator standing in the Diagnostics Building, some 30 metres distant?
Convenient images, of course, simplify reality. Here is a little more explanation on this one:

"The top and bottom halves of the central solenoid are attracted to each other with a force of 50,000 tonnes," explains Neil Mitchell, the head of ITER Magnet Division. "If there was a gap in the middle of the 18-metre-high component, and if a 100,000-tonne aircraft-carrier was attached to the bottom, the carrier would indeed be lifted until the gap closed."

This leads to the naive question of the week. If the massive magnet is powerful enough to lift an aircraft carrier, could it snatch the car keys from the pocket of an operator standing in the Diagnostics Building, some 30 metres away?

Powerful magnets are known to do this kind of trick. Paul Libeyre, ITER Central Solenoid, Support and Performance Section Leader, remembers visiting the Philips research centre in Eindhoven (Netherlands) where some of the most powerful magnets for magnetic resonance imaging (MRI) are assembled.

"They did several demonstrations on how a powerful MRI magnet attracts anything metallic in its vicinity with considerable force—coins, trays, drip stands, and even a wheelchair! It was quite impressive."

The keyword here is "vicinity." Like many things in nature (light, radiowaves, gravity, sound ...) the intensity of a magnetic field follows what is called the inverse-square law. The force of a magnet decreases so rapidly that at a distance of 30 metres it has lost 99.9 percent of its original intensity.

In the pocket of the diagnostics operator, therefore, car keys are perfectly safe.


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