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A major international agreement between the European Community, the United States and Japan for cooperation in the field of research on controlled nuclear fusion is to be signed in Munich on 15 January 1986. The agreement associates the three largest tokamak-type (1) experimental fusion devices in the world: JET, which has been built at Culham in the United Kingdom as part of the European Community's fusion programme, TFTR, which is installed at Princeton (United States), and JT-60 at Naka-machi (Japan). As described in the agreement, the cooperation between the three centres will take many different forms: more extensive exchanges of information and researchers, joint preparation of certain research programmes, joint organization of symposia, etc., it being possible to conduct all these activities on either a trilateral or a bilateral basis. = In the current state of research, physicists generally consider it more than likely for it to be in a tokamak that the scientific feasibility of fusion will be demonstrated. More precisely, they take the view that such demonstration is possible in the large second-generation tokamaks such as the European JET, the American TFTR or the Japanese JT-60. This is what makes the cooperation agreement between these three facilities so important: it makes it possible further to consolidate the most advanced concept in the nuclear fusion field and will help speed up future developments. For the European Community, the agreement represents the possibility of retaining and strengthening the position they have gained in the forefront of the field by dint of twenty years' sustained effort. It is in line with the Community's firm policy of international cooperation in the fusion field, which has already produced a number of bilateral agreements with Sweden, Switzerland and the United States. The agreement will be officially signed on 15 January at the Max Planck Institute for Plasma Physics at Garching (near Munich) by the respresentatives of the different institutions concerned: Mr Fasella (Director-General for Science, Research and Development at the Commission of the (1) The term "tokamak" of Russian origin means "toroidal magnetic chamber" and describes the configuration of the vessel in which the fusion process takes place. - 2 - European Community) for Euratom and the JET Joint Undertaking, Mr Trivelpiece for the US Department of Energy and Mr Mori for the Japanese Atomic Energy Research Institute (JAERI). The signing ceremony will be attended by Mrs Steeg, Director-General of the International Energy Agency, under the auspices of which the agreement was drawn up, and Mr Palumbo, Director of the Community's fusion programme and Chairman of the Agency's Fusion Power Coordinating Committee. It will be preceded by a welcoming address by Prof. Pinkau, Director of the Plasma Physics Institute, and followed by a press conference. - - - - - - - - - BACKGROUND Controlled thermonuclear fusion is a gamble that physicists have for many year been endeavouring to win. If fusion could be achieved in satisfactory operating conditions, it would constitute a virtually inexhaustible source of energy; such a prospect is, however, in the realm of the fairly distant future. Research currently in hand throughout the world is merely aimed at demonstrating the scientific feasibility of fusion, namely the possibility of producing a fusion reaction with a positive energy balance, i.e., one that releases a greater amount of energy than that employed to produce it. Once this has been demonstrated, it will clearly remain to be determined whether fusion reactors are technologically possible, economically advantageous and as safe to operate as they appear today. The sun and the stars derive the energy they release from nuclear fusion reactions: as their name suggests, such reactions consist in the fusion of two nuclei of light atoms to produce a heavier nucleus. The process is accompanied by the release of a large amount of energy. In order to be set off, it requires extreme temperature and density conditions: inside the sun, fusion reactions take place at a temperature of 15 million degrees celsius. In order to achieve fusion on earth, without the aid of the extremely strong gravitational force of the sun, it is necessary to attain even higher temperatures, in the region of 100 million degrees. At such temperatures, matter exists in a special state, called plasma: a mixture of ions (electrically charged nuclei) and electrons. The fusion reactions that appear most promisisng are those involving two isotopes of hydrogen: deuterium and tritium. These isotopes are universally available in extremely large quantities: water contains deuterium, while tritium can be obtained from lithium, an element that occurs plentifully in - 3 - the earth's crust. Fusion of the deuterium and tritium nuclei produces a nucleus of helium while releasing a high- energy neutron. As in a fission reactor, deceleration of that neutron in an outer "blanket" produces heat that can be utilized conventionally to generate electricity. Two methods are currently being investigated with a view to achieving the deuterium-tritium fusion reaction on earth. The first, called inertial confinement, involves compressing, with the aid of beams of laser photons or charged particles, a target containing the two elements in the solid state. An extremely dense plasma is thus obtained for a very short time. The second method - magnetic confinement - consists in confining, with the aid of magnetic fields, a less dense but extremely hot plasma for a longer period. The magnetic fields act as a vessel in this case, for no physical container would be capable of withstanding direct contact with such high temperatures. In the context of this second method, different magnetic configurations have been designed and tested. A distinction is drawn between "open-ended", or linear, and "closed", or toroidal (ring-shaped), configurations. In the former (for example, "mirror machines"), the plasma is contained in a long cylinder. In the latter (which because they are closed, have the advantage of not posing any particle- leakage problems), the plasma is confined in a torus-shaped space. Among the machines of this type, the most promising and widelyd-researched concept is the "tokamak", which was inaugurated some twenty years ago by the Soviet Union (tokamak being an acronym for the terms "toroidal magnetic chamber" in Russion). Other systems exist ("stellarators" and "pinch machines"), which are sufficiently similar to the tokamak concept to be able to benefit from progress made therein if they proved in practice to be superior. The European Community is coordinating and financing a major fusion research programme almost exclusively devoted to magnetic confinement in the toroidal configuration. This programme, the cornerstone of which is currently JET, is chiefly concerned with the tokamak system; it nevertheless also includes research on the two other toroidal configurations, namely stellarators and pinchmachines.