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The JET Machine: Design, Construction, and Operation of the Major Systems

M. Huguet, K. Dietz, J. L. Hemmerich, J. R. Last

Fusion Science and Technology / Volume 11 / Number 1 / Pages 43-70

January 1987

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The basic parameters of the Joint European Torus (JET) machine are presented together with the reasons that guided their choice. The design principles followed during the conceptual phase are also described. Existing technology and modular design were used as far as possible, with a view to reducing the technological risk and to make the machine easily maintained. For each of the main components of the machine, the design and manufacturing techniques are reviewed in some detail The vacuum vessel is an all-welded Inconel structure, bakable at 500°C, to achieve a base pressure in the range of 10-9 mbar at room temperature. The water-cooled magnet coils are made of copper with epoxy resin based insulation systems. The mechanical structure employed massive castings and stainless steel parts with high-precision machining. The assembly of the JET machine took 1 yr and used specially designed lifting and assembly jigs. The assembly and commissioning procedures are outlined for each component. The operating history of the vacuum vessel and associated systems, such as the pumping and bakeout systems, is presented. These systems have operated satisfactorily so far and have achieved their design specification in terms of the vacuum quality. The gas partial pressures in the vessel are typically 2 × 10-7 mbar for hydrogen and <10-9 mbar for impurities, at 230°C. The behavior of internal wall protection and limiters during the initial JET operation is described. Future plans are outlined that include graphite protection and a toroidal belt limiter. The advantages and drawbacks of wall conditioning techniques, such as pulse discharge cleaning, glow discharge cleaning, and carbonization are given. The JET toroidal field coils have been commissioned and used routinely up to their maximum design performances (i.e., 67 kA with a total energy dissipated per pulse of 5 GJ). Operation is monitored through an instrumentation system, which includes a short circuit detection system. The ohmic heating coils have also been commissioned to their maximum design performance. Some modification of these coils are envisaged in order to be able to extract the full flux swing during plasma operation. So far, the outer poloidal field coils have been used up to currents that are no more than one-third of their design values. This is because the plasmas achieved have a low β and do not require a large vertical field to maintain equilibrium.

 
 
 
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