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JET, mission accomplished - and the future

   
 
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With ITER, which has a much larger volume than JET, it should be possible to maintain combustion of a deuterium-tritium mixture for long enough to provide final proof of the practicability of fusion.
Breaking one record after another, JET - the largest facility in the world for studying thermonuclear fusion - has completed the missions originally entrusted to it, exceeding all expectations. The scientific and technical basis has now been laid for demonstrating net fusion energy production: the high-tech ITER project requires partnership at a global level. Fusion may well meet the double requirement of this century: to secure the energy supply needed for economic and demographic development while avoiding additional emissions of greenhouse gases.

According to Umberto Finzi, principal advisor for Fusion activities to the Director-General of the Research DG, the pace of global economic and demographic development over the coming decades will be such as to require setting up a new 1 gigawatt power station every week. In his opinion the goal of sustainable development obliges us to find a way of generating electricity which restricts the emissions causing the greenhouse effect; the problem is so serious that no potential solution, whether fission, fusion or renewable energy, must be disregarded. "At the world level the prospect for undertaking the Next Step in fusion development have never been in the past as good as they are today." he says.

Energy produced through the fusion of light atoms has a number of unquestionable advantages: abundant fuel, no long-term hazardous waste, no risk of the reaction getting out of control. In addition, no greenhouse gases are emitted and no transport of radioactive material occurs in the plant daily operation. However, achieving sufficient nuclear fusion for net energy generation requires the development of highly sophisticated technology and large-scale equipment and therefore the mobilisation of international resources.

JET propels global research
Launched at the end of the 1950s, the European Union's Fusion programme encompasses all the research undertaken in this field in the Member States of the EU (plus Switzerland). It has enabled Europe to become a leader in the field, in particular thanks to JET (Joint European Torus), the foremost facility in the world, located in Abingdon (United Kingdom).

All the technology employed in fusion devices like JET is intended to overcome the electrostatic repulsion of nuclei which keeps them apart. The fuel used is hydrogen, more specifically a gaseous mixture, called plasma, of heavy isotopes, tritium generated at the plant from lithium (abundantly present in the earth's crust) and deuterium (abundant in seawater: approx. 30 g/m3). Fusion of deuterium and tritium produces a helium atom, a neutron (used to generate tritium) and an energy surplus of 17.6 MeV. This means that 1 gram of DT fuel can produce about 3-4 . 1011 joules of energy, equivalent to burning 20 tonnes of coal. There are three parameters that have to be controlled: density, temperature, and confinement time. Nuclear density must attain 1020 particles/m3 and temperature must exceed over 100 million degrees. At such temperatures the fully ionised plasma must be kept away from the vessel walls as any contact would dislodge contaminant atoms from the walls, causing plasma energy losses. The confinement time of this energy must not be less than a few seconds. The approach adopted in this research, in particular in the JET installation, consists of confining the plasma using an intense magnetic field inside a toroidal (tyre-shaped) chamber.

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The first installation capable of operating with a deuterium-tritium mixture, JET produced 1.7 MW fusion in 1991. Beaten by the American TFTR facility (10.7 MW) three years later, it took the lead again in 1997 by attaining 16.1 MW (65% of power injected) using a new technique.

From success to records
Built between 1978 and 1983, JET was designed to obtain and study plasmas under conditions approximating those of a reactor. Most of the experiments were carried out with deuterium alone. Valuable data were thus obtained on the behaviour of plasmas and the effect of heating techniques and magnetic configuration on confinement quality. Studies of plasma-wall interaction led to the development of new materials and to the installation in the early 1990s of a magnetic deflector (known as a divertor) which produces magnetic field lines causing particles coming out of the plasma to be deflected towards plates away from the plasma inhibiting the entry of any impurities which are released.

In 1991 JET was the first installation to be capable of operating with a deuterium-tritium mixture. Its fusion output was 1.7 megawatts. Beaten in 1994 by the American TFTR installation (10.7 MW), it took the lead again three years later by attaining 16.1 MW (i.e. 65% of the power injected), using a new operational technique.

ITER, the next key stage
With a much larger volume than JET, ITER should be able to maintain combustion of a deuterium-tritium fuel mixture for long enough to provide the ultimate proof of the possibility of using fusion. Currently in the design stage, ITER is the fruit of large scale co-operation between the European Union, Russia, Japan (until mid-1999) the United States. 

According to a physicist in the Fusion programme, the recent results of JET have greatly strengthened confidence in the validity of the ambitions of the ITER project; in particular, it has been found that 25% less power than expected is needed to achieve the optimum confinement regime: with the deuterium-tritium mixture, plasma confinement has produced better results than just using hydrogen.

The 5 000 people taking part in the Fusion programme, of whom about 2 000 are researchers, are ready for the next stage. The ITER design project has been worked out down to the finest details and a virtual model of the machine is currently being constructed. Many industrial partners have participated in the design, manufacturing and testing of prototypes. The main obstacle to building ITER is financial, and a more modest variant of the original design has been developed, with a substantial reduction in overall cost while maintaining the overall objectives. What remains to be done is choosing the site and taking the political decision to complete the project, a decision that will have to be taken in 2002-2003. It is a decision that will affect the long-term ecological future of the planet.

 

Project Title: Joint European Torus (JET) 
Programme: Nuclear Fusion Programme

CORDIS databaseFor more information on this project, and the Fusion Programme,
go to the
CORDIS database record and to the RTD energy web site:
http://ec.europa.eu/research/energy/index_en.html

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