Effective thermal properties of limiter graphite

A brief review is given of a frequency-dependent thermal wave technique with audio-acoustic detection which is used to measure the thermal properties of solid state samples in comparison to reference materials of known properties. Two artificial graphites (Schunk & Ebe FP159I and Carbone Lorraine 5890PT) which have been used as limiter materials in the tokamak devices ASDEX and JET are analysed. A depth-dependence is found for the effusivity k ϱ c , the thermal parameter governing the temperature rise of the limiter surface after short intense heat pulses. The absolute value of the effective effusivity at the surface and that of the subsurface layers are determined. This thermal depth profile can be represented by a three-layer model and is related qualitatively to the surface roughness and volume porosity of the graphite plates.