Modification of the JET vacuum vessel support and restraint system

Since 1983, after the first plasma vertical instability, the support and restraint system has been continuously modified and upgraded to cope with the new design and operational requirement. Fig. 1 shows how the vessel supports and restraints have changed over the life of JET. With the divertor phase, new loads are applied to the vacuum vessel supports and restraints leading to a revision of the complete system. The elastic suspensions at the equatorial plane have been modified to cope with the increase in vessel weight. The vessel restraints have been modified and tested to cope with the new electromagnetic load in equilibrium and plasma instability. This paper briefly describes the overall philosophy of the vessel support system, the modification and the tests that have been done. Some experimental results are also reported on the behaviour of the supports and restraints. (orig.)