Speaker
Description
In the EU DEMO fusion reactor, currently in its pre-conceptual design phase, the long plasma pulse duration and the large thermal loads represent a challenge for the power exhaust, so that a new, robust design of the divertor is needed. For this reason, several DEMO-relevant divertor solutions will be tested in the Divertor Tokamak Test (DTT) facility that will be built in Italy. It will be a fully superconductive compact tokamak, very flexible in terms of plasma configurations.
The 18 Toroidal Field (TF) magnets, cooled by forced-flow supercritical helium at 4.5 K, must then be reliable components, capable to cope with several different operating scenarios. To protect them (and the entire machine), the possibility of a fast discharge of their magnetic energy by means of dump resistors is foreseen.
The 4C code, aimed at the analysis of thermal-hydraulic transients in superconducting magnets, is used here to develop a detailed model of the DTT TF coils. The model will be used to analyse parametrically the fast discharge and optimize the dump time constant. The latter will indeed be limited by two main constraints: on the one hand it must be sufficiently large not to develop a voltage that can damage the electrical insulation, with a serious impact on safety and reliability aspects which are fundamental for an expensive nuclear fusion experiment; on the other hand, the heat deposited by AC losses in both cable and supporting structures during the current and magnetic field variation can lead to a quench, so that it is desirable to reduce the transport current as fast as possible to reduce the hot spot temperature and thus the thermo-mechanical stresses possibly damaging the cable (and, again, impacting on the magnet system reliability). An optimum range for the dump time constant is then proposed as a guideline to the magnet system designers.
