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Fusion by magnetic confinement: the long road from dream to experimental realisation

Philippe GHENDRIH, Institute for Research on Fusion by Magnetic Confinement, CEA Cadarache.

Research on magnetic confinement fusion must demonstrate the peaceful use of thermonuclear energy. The possibility of such an energy source is part of the cycle of the great discoveries of physics at the beginning of the 20th century. The issue became political and today, beyond the hazards and dissensions, it is the subject of an international collaboration between seven partners for the construction and operation of ITER in Cadarache (France), the site proposed by the European partner.
ITER is an experimental device for the confinement of a plasma by a magnetic field in a configuration called a tokamak. It is a threefold challenge: organisational, with the implementation and construction; technological, with a prototype that is a concentrate of high technology, making ITER a paradise for engineers; and finally, a challenge for physics, that of obtaining a plasma in a thermonuclear combustion regime.
Plasma is the fourth state of matter, produced when atoms split into charged nuclei and free electrons. This charged medium is then sensitive to electromagnetic forces. An intense magnetic field is therefore used to confine this plasma and raise it to hundreds of millions of degrees, the temperature that must be reached for the energy production balance to be profitable. Although classical - it is only marginally relativistic and quantum effects are limited - tokamak physics is that of a complex system. It aims to combine objectives that appear to be antinomic: a high confinement performance in the centre of the plasma and a heat deposit on the walls that avoids accelerated ageing of the latter. In both cases, the central element is heat transport by turbulence. The latter is associated with the self-organisation of the electric field. Surprisingly, this physics is very similar to that of flows in planetary atmospheres.
After evoking the history of fusion, ITER and its construction, the challenges of current research will be discussed, in particular the physics of turbulent transport. In this context, the numerical simulations, accumulating millions of hours of calculation on supercomputers, will be presented. They constitute a new front of knowledge and new challenges for research.

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