Characterization of nonlinear thermophysical properties of carbon layers deposited on the tiles of the JET tokamak divertor


J. Gaspar1, J. Gardarein1, F. Rigollet1, C. Le Niliot1 and Y. Corre2

1IUSTI UMR CNRS 6595, Université de Provence Marseille, France
2CEA/IRFM, St Paul lez Durance, France

Keywords: non linear, thermal conductivity, conjugate gradient method, infrared measurement
property: thermal conductivity, thermal resistance
material: carbon

In areas of high heat fluxes in JET (Joint European Torus) tokamak, the plasma erodes carbon composite tiles. A redeposition of eroded carbon then occurs on other tiles in lower heat fluxes areas. The temperatures measured by infrared thermography on the surface of carbon deposits during unsteady experience are then much higher than those of the tiles without deposits. In order to exploit these infrared measurements and deduce at eachtime the plasma heat flux absorbed by the component, it is therefore necessary to know the thermophysical properties of the carbon deposit. Given the non uniform conditions of redeposition inside the machine, these properties may depend on the position on the tile (thickness of the deposit and contact resistance may vary). Moreover, given the measured temperature rises of several hundred degrees, a dependence of these properties with temperature is possible.

We aim to solve here the inverse problem of estimating the field of equivalent thermal resistance of carbon deposit. Because of symmetry in the tokamak, the field depends only on one spatial dimension to the surface of the tile, but it also depends on the temperature, and then time during an unsteady experiment. The surface measurements used are provided by an infrared camera. The shape of the incident plasma heat flux is assumed known. The conjugate gradient method ([1], [2]) is used for identification, the three associated problems (direct, adjoint and sensitivity problems) are solved using the finite element method with the software CAST3M. The identification results will be presented with noisy numerical data and with real data.

References
  1. Cheng-Hung Huang, Sheng-Chieh Chin. Int.J. Heat and Mass Transfer 43 (2000) 4061-4071

  2. Y. Jarny, M.N. Ozisik, J.P. Bardon. Int. J. Heat Mass Transfer 34 (1991) 2911-2919

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