M. Poier, T. Denner
Institut fur Plasmaphysik, Forschungszentrum Juelich GmbH, EURATOM Associaton. Trilateral Euregio Cluster, D-52425 Juelich Germany
At TEXTOR 94 the Dynamic Ergodic Divertor (DED) will be installed, in order to influence transport parameters at the plasma edge and to study the resulting effects on heat exhaust, edge cooling, impurity screening and plasma confinement. As described previously [1] the preliminary design foresees a layer of divertor target plates which accommodate the heat load from the plasma.
The magnetic field coils of the Dynamic Ergodic Divertor, which are located behind the divertor target plates, must be protected from energy flux, that is radiated from the target plates. So the maximum working temperature of the coil tube will be limited to 2500 C. As shown in a parameter study about the thermal load on the target plates [2] a thermal isolation between the target plates and the DED coils is necessary. In this paper the election and testing of isolating materials and the final design of the divertor target plates in combination with the isolation is described.
According to the results of the parameter study the isolation material should have high bulk density and heat capacity and low thermal conductivity and emissivity. This requirements led to several materials which were tested in three steps. First the thermal-shock resistance was tested by simulating the expected heat load in a vacuum test vessel. Outgassing rates were measured and analysed. Second the shock-treated samples were tested in a transverse bending test and compared with not shock-treated samples. Third the possible candidates were studied according to their availability, price and shapability.
As a result of these three steps a preliminary Divertor design was made which is now implemented into the design of the DED. The paper describes the requirements of the DED divertor plates, the test devices and the performance of the test. The testing results are listed and the final design of the divertor plates and isolation is shown.
[1] B. Giesen, proc. Of 16th IEEE/NPSS Symposium on Fusion Engineering SOFE 95, (1995), Vol. 1, 712-715
[2] T. Denner, M. Poier: Thermal Load on DED Target plates