Thermal properties of plasma exposed carbon and heat flux calculations on a spatial scale of a few microns

Heat flux calculations on the basis of surface temperatures measured thermographically are used at different tokamaks. The spatial resolution of the temperature measurement is in the order of a few millimetres to cope with the expected heat flux gradients. The reliability of the calculated heat flux depends on the degree of agreement between the numerical model and the real situation. This paper discusses effects which alter the measured surface temperature and have to be considered in the heat flux calculation. An inhomogeneous temperature distribution in the field of view of a single detector results in a temperature measuring error which is highest (10%) for a hot component below 50% filling ratio. The limits for the applicability of analytical solutions of the heat flux equation are discussed. Finally, the variation of thermal properties of fine grain graphite and carbon fibre composite on a spatial scale of a few microns, based on experiments presented in [A. Herrmann, M. Bohmeyer, et al., Phys. Scr. T 111 (2004) 98], is presented.