ITER: a world wide experiment on fusion
Jean Jacquinot
Cabinet of the High Commissioner for Atomic Energy
31-33 rue de la Fédération 75752 CEDEX 15
In the 21 century, once oil and gas will have become in rare supply, our society will have to face the major challenge of having access to the energy resources required for its sustained development. Coal could still be available for more than 200 years, but its massive use is likely to have profound negative effects on our environment.
Clearly a sharp increase of research activities are required in a wide range of energy topics ranging from mastering energy consumption, renewable energy sources and nuclear energy. Nuclear energy can be harnessed via fission of very heavy atoms or fusion of light nuclei such as the isotopes of hydrogen. Nuclear fission is a well proven process already used to produce electricity without emission of greenhouse gases. France produces 78% of its electricity in this way. However, in this area progress is needed with regards to a more intensive use of the uranium extracted ore (presently 0.5%) and to long lived radioactive waste production. Fusion, on the other hand, would provide major advantages in these domains. It powers the sun and is the most common form of energy in the known universe. Its controlled use on earth, however, requires a challenging phase of scientific and technical development.
Research in controlled nuclear fusion for peaceful application started forty years ago. All the nuclear basic concepts required for fusion are known since the early days. The physical criteria for a net power gain using magnetic confinement devices were soon derived from the basic concepts and have changed very little since. At the time, these criteria did not seem so formidable to achieve: A very dilute gas (about 10 20 particles per m 3) has to be heated at a temperature of about 100 million degrees and the characteristic time of its energy confinement has to be in excess of one second. This corresponds to a gas pressure in the range of 1 to 4 atmospheres which is balanced by the confining magnetic field.
However, at high temperatures, the gas becomes fully ionised. Such a medium, called plasma, is dominated by the collective interactions of its charged constituents (ions and electrons). The fundamental physics laws of plasmas were largely unknown in the early sixties and early attempts to confine plasmas with magnetic fields failed to achieve the criteria by a long way. The plasma escaped confinement through instabilities and turbulence phenomena of extraordinary diversity. Clearly, one had to establish the physics first before going further. This was done in the sixties and the seventies and led to the concepts and experimentation of toroïdal confinement devices. In particular, the Tokamak concept discovered by the Russian scientists of the Kurchatov institute was successful to achieve global stability of hot plasmas. Following this discovery, large machines such as JET in Europe, TFTR in the USA and JT-60 in Japan have been built in the last 20 years and have demonstrated successfully the possibility to confine plasmas of thermonuclear grade. JET first operated with deuterium tritium mixtures, obtained in 1997 a record 16 MW of fusion power, demonstrated heating by fusion released alpha particles and achieved near power breakeven conditions. TFTR also exceeded the 10 MW power level and reached record temperatures. JT-60 obtained, in deuterium plasmas, conditions equivalent to breakeven in D/T. Many smaller tokamaks of various shapes, size, magnetic field and pulse length capability were built around the world. They could all be operated with good global stability and showed that energy confinement was dominated by micro scale turbulence developed fully in the non linear regime. The turbulence could be much reduced locally where large sheared flows were generated spontaneously. The process is analogous to the tochocline in the sun. Even with the largest existing computers, it is not possible to calculate, from first-principle, the particle and energy transport across the magnetic field in the entire plasma. Theoretical modelling and similarity approaches are therefore important tools. A protocol could be established among nearly all Tokamak experiments in order to cast their data in a physics-based dimensionless form so that an international confinement data base could be assembled and ‘wind tunnel experiments’ could be coordinated. Scaling laws were then derived and extrapolated to define the parameters of a machine capable of providing a large fusion gain (figure 1). This methodology was the base for the physics design of ITER.
ITER, “the way” in Latin, is an international project involving the People’s Republic of China, the European Union (represented by Euratom), Japan, the Republic of Korea, the Russian Federation, and the United States of America, under the auspices of the IAEA. The cooperation, started in 1992, has led to the detailed engineering design for an experiment (figure 2) capable of generating repetitively 500 MW for 400 s with a power gain of 10. The international team also carried detailed costing based on industrial experience and conducted a programme demonstrating the availability of the required key technologies based on the construction of large scale prototypes. Most notably, large magnets based on NbTi technology and capable of pulsed operation were built and achieved the design parameters. Other prototyping included plasma facing materials, robotics, heat removal systems, advanced plasma heating and a module of the vacuum vessel. From a general stand point, ITER will have to bring together several leading-edge technologies working safely in combination.
The design was completed, reviewed extensively and approved by the partners in 2001. Negotiations then started aiming at defining the international organisation for construction and operation. It was, in particular, decided that ITER will be procured essentially ‘in kind’, each partner being responsible to supply through a domestic agency a major element of the machine. The host would procure, inter alia, the non transportable elements such as the buildings and the assembly of the machine. The site selection process was highly competitive among 4 well thought out proposals and lasted 2 years. It illustrated the high level of commitments of the partners for the success of ITER. On 28 June 2005, Cadarache, the site proposed by the European Union (figure 3) was selected to host the project. It is located in Provence in the South East of France. It is adjacent to, but independent of, the CEA energy research centre established here since 50 years.
The negotiations between Europe and Japan also resulted in a broader approach to the development of fusion encompassing research on material under irradiation by fast neutrons, advanced Tokamak operation and a new data analysis and computing centre. In fact, the construction of ITER will not preclude a world wide accompanying physics programme on all aspects of fusion science and technology
At the time of writing, the organisation of ITER is taking place on three separate levels: -International: first arrival of the team on site is expected in 2006 – Partner level: with the creation of the 6 domestic agencies - Finally at the French level with the preparation of the site, the welcoming organisation and enhanced scientific support.
An exemplary scientific collaboration of unprecedented international size is being put in place.
Figure 1
Comparison of the international data base from 13 devices with the confinement scaling law (projection for ITER : top red square)
Figure 2
Cut-out representation of ITER (cryostat in blue, magnetic coils in brown, lavender and purple)
Lay out foreseen for the ITER installation in Cadarache (French fusion centre in the foreground)