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World's biggest freezer to cool hotter-than-the-sun reactor

The cryogenic plant will be used to cool the electromagnets that generate the intense magnetic fields which will contain the hot plasma inside the reactor.© ITER Organization
The cryogenic plant will be used to cool the electromagnets that generate the intense magnetic fields which will contain the hot plasma inside the reactor.© ITER Organization

Engineers are starting work on the world’s biggest freezer – a giant cryogenic plant that will cool parts of the International Thermonuclear Experimental Reactor (ITER) to a fraction above absolute zero.

ITER is an internationally funded nuclear fusion reactor being built in southern France which, if successful, could solve much of the world’s energy needs without producing radioactive waste.

In order to do so, it aims to produce energy through the same nuclear reaction that powers the sun. But, while the centre of the sun burns at 15 million degrees Celsius, the hydrogen inside the ITER reactor will be heated to some 150 million degrees Celsius.

At that temperature, electrons are ripped off individual atoms to form plasma inside the reactor, where nuclei float in a sea of electrons.

The high temperature means the plasma cannot be allowed to touch the sides of the reactor. So it will be suspended in a vacuum within a toroid – a doughnut shape – using some of the world’s most powerful magnets.

That’s where the cryoplant comes in – these electromagnets are made from coils of superconducting wire that are cooled using liquid helium. Parts of the system need to be cooled to temperatures as low as minus 269 degrees Celsius, or four kelvin, which is four degrees Celsius above absolute zero, the lowest temperature theoretically possible.

While the copper wire used in standard electromagnets loses heat and energy during operation, the supercooled niobium-titanium and niobium-tin wire used in the superconducting magnets can conduct very large electrical currents with no loss of energy.

It is these electrical currents that will generate and sustain the intense magnetic fields required to contain the hot plasma.

Cooling power

Technically, the cryoplant that is being developed for ITER isn’t one plant but three plants that will work together as one to produce the cooling power required. The plant contains three stages: a liquid nitrogen plant that operates at minus 193 degrees Celsius, a liquid helium plant that produces cooling power at minus 268.5 degrees Celsius, and a cryogenic distribution system that further cools the helium to the temperatures required.

Although similar-sized single units are in use elsewhere in the world, for example to cool the superconducting magnets for the world’s largest particle collider at the European Organization for Nuclear Research (CERN), they have never been used in parallel before.Aerial view of the ITER construction site, 2014.© LESENECHAL/PPV-AIX.COMAerial view of the ITER construction site, 2014.© LESENECHAL/PPV-AIX.COM

The difference between CERN and ITER is that at CERN the cooling power is distributed around the 27 kilometre Large Hadron Collider in eight separate plants, while at ITER all the cooling power will be combined into one plant and will be focused on one 25-metre-wide reactor.

Fusion for Energy (F4E), the organisation responsible for Europe’s contribution to ITER, said that the main difference between the ITER and CERN cryoplants is their power.

Marc Simon, the technical officer responsible for the liquid nitrogen plant at F4E, said: ‘The difference between ITER and all the other facilities in terms of cryogenic power is that here we have in a single place a plant that is twice as powerful as others.

‘The difference between ITER and all the other facilities in terms of cryogenic power is that here we have in a single place a unit that is twice as powerful as others.’

Marc Simon, Fusion for Energy

‘We need a plant that is twice as powerful as a single unit and all in the same place working together, this makes it the biggest cryogenics system in the world.’

Cryogenic pumps

As well as supplying the liquid helium for the magnets, the cryoplant will also help maintain the vacuum inside the reactor via a set of cryogenic pumps.

These cryogenic pumps trap gases and vapours by condensing them on a cold surface. At temperatures close to absolute zero, gas inside the reactor will be attracted to the pump and freeze onto its cold surface.

The contracts to design and manufacture the cryoplant have been awarded to Air Liquide, a French company that specialises in gas technology. Xavier Vigor, the head of the company’s advanced technologies division, said that the project will be a chance for the company to develop.

‘For ITER, we will design and manufacture the biggest cryogenic helium plant in the world – three times bigger than the last plant we manufactured (and) that was already the largest in the world,’ he said. ‘We will expand our competencies in the cryogenic field and we hope to be able to re-use these competencies and human resources for future projects.’

However, the scientific and technological challenges involved are huge and it’ll take almost ten years until the first test reactions, which are planned for 2023.

ITER

The seven parties collaborating on ITER are China, the EU, India, Japan, Russia, South Korea and the United States. Together, they represent roughly 50 % of the world’s population and 80 % of the global GDP.

The EU is making the largest contribution to the project. As well as hosting the reactor and being responsible for constructing most of the buildings at the site, it is responsible for supplying 45.5 % of the components.

The EU budget for the project is EUR 6.6 billion and its share of the components will be produced by organisations based in the EU, helping European research make the transition to new technology, promoting employment, and allowing companies to familiarise themselves with new markets and technology sectors.

For details, visit http://www.iter.org/

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