Superconducting magnets will be about one third of the building costs of the International Thermonuclear Reactor, to be built in Cadarache in France; this experimental reactor aims at delivering 500 Megawatt by nuclear fusion. November 2006, the participating countries have signed the contracts for building this reactor. Parallel to this, the G8 countries have placed nuclear fusion high on their agendas as a sustainable way of generating energy.
The magnets are crucial in keeping in control the plasma, in which fusion takes place. They exist of giant coils of superconducting cables. Losses in the cables during control of the magnets results in loss of magnetic fields as well. Well-functioning of the reactor is therefore highly dependent of cables with minimal losses and degradation in time. From all participating countries, reference cables are sent to the University of Twente for testing. One single test takes about two weeks, and the scientists estimate to receive 20 samples for testing.
The currents through these cables and the magnetic fields are extremely high: over ten thousand Amperes and 13 Tesla, respectively. This results in very strong mechanical forces on the cables. The separate wires of which the cable consists, are already protected by a heavy steel mantle, but still they are pressed together by the strong forces. In the lab, these forces are simulated. The cable therefore is cooled down to 4.2 Kelvin (minus 269 degrees Celsius), which is the normal operating temperature. A strong mechanical press simulates the forces present under normal operation. Would temperatures rise too much caused by this pressure, the wires loose their superconductivity and the magnetic field disappears, resulting in a vanishing plasma.
The European Domestic Agency, responsible for the European contribution to ITER, chose the Low Temperature Division because of the extensive knowledge of and experience with the behaviour of superconducting cables. The group is highly reputed in the worldwide research area. Thanks to this experience, the scientists already proposed essential design improvements for the cables, resulting in less degradation and a reliable and economical way of operating the cables during the entire life of the reactor. The first cables using the ‘Twente model’ have already been made.
Nuclear fusion is seen as one of the answers to the worldwide energy issues: it is clean, safe and sustainable and does only produce short-living radioactive waste. The energy is generated from melting together light and heavy atomic nuclei, within a plasma at extremely high temperature. Nuclear fusion is the energy source of the sun and the stars. Compared to fossil fuels, this source of energy is inexhaustible.
The test site is developed by scientists of the Low Temperature Division led by prof. Horst Rogalla. The High Current Superconductivity section of this group takes care of the ITER-tests and is part of the Institute for Mechanics, Processes and Control Twente (IMPACT). The tests are coordinated by Mr. Arend Nijhuis.
Wiebe van der Veen | alfa
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