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The ITER pre-compression ring system is based on two sets of 3 rings made in fibreglass-epoxy composite and is located on top and bottom of the inner straight leg region. These rings will provide a radial force of about 70 MN/coil (35 MN at the top and 35 MN at the bottom) under cryogenic conditions, pulling the TF coils into contact, reducing the gap between the poloidal shear keys and their keyways during operation and also reducing the toroidal tension in the four outer intercoil structures bands. The paper describes the stress relaxation test performed in ENEA Frascati laboratories on a reduced scale glass fibre-epoxy composite ring. The ring was manufactured with a diameter of 1 m (1/5 of the real scale one) by winding S2 glass fibres then impregnated with epoxy. The volumetric glass content was of 69% and no significant presence of defects was verified by an X-ray survey. The test has been carried out following as close as possible the ASTM standard E 328-86. The ring has been inserted into a dedicated hydraulic testing machine consisting of 18 radial pulling actuators and then loaded up to a ring membrane hoop stress of 800 MPa. The deformation has been maintained constant during the test by inserting a solid steel disk in the machine centre restraining the machine radial motion. Average hoop stress has been daily monitored measuring the force required to lift the ring just free of the constraints during the test period. The ring performed 125 testing days showing no significant stress relaxation and a small reduction of the ring stiffness that appeared mainly in the first days of the test.

The FTU tokamak will have to operate steadily at high magnetic fields in order to reach the expected performance. Its magnet and vacuum chamber, due to thermal and electromagnetic loads, will undergo very high stresses for a large number of shots. In order to assess the feasibility of the components, numerical codes to compute current, magnetic field and temperature distributions, and extensive three dimensional finite element stress analysis have been developed. The main results obtained are illustrated.

This paper deals with the work done to define, construct and test a detailed critical part, spatially limited at about 10 cm3, reproducing the essential configuration of the FT-U magnet coil. The tests were performed at room and LN 2 temperatures in order to study the degradation of the insulating materials after repeated mechanical stresses. We describe criteria required to design a practical model with the possibility to simulate the thermo- -mechanical behaviour of the coil and allowing the measurement of the electrical insulation properties. The experimental set-up is described, as well as the operations for test analysis, optical observations and measurements on the components. Finally some results and typical microphotographs are reported.

In order to reduce the energy consumption and improve the mechanical characteristics of the structural materials, the FTU (Frascati Tokamak Upgrade) machine operates at -196°C. In the following, the cryogenic system of the FTU machine is described.

Raising the JET maximum toroidal field from 3.45 to 4.0 T results in increased forces and stresses in the key machine components during normal operations and disruptions. These forces and stresses have been predicted for 4.0 T operation and compared with allowable values derived from tests on used and spare JET coils. In this assessment significant lessons related to the design, manufacture and operation of key Tokamak components have also been learnt. (C) 2001 The European Commission. Published by Elsevier Science Ltd. All rights reserved.