Photoacoustic measurement of effective thermal properties of rough and porous limiter graphite

Abstract

The photoacoustic amplitude and phase lag of rough and porous graphite limiter plates, before and after exposure to plasma discharges in Tokamak devices, have been measured and interpreted to obtain a quantitative description of the effective thermal-depth structure. The effusivity (kρc)1/2, the relevant thermophysical parameter for time-dependent surface heating, of the measured samples shows depth profiles, which can be approximated by a three-layer model. Before exposure to plasma discharges, this depth profile can be related to the surface roughness and volume porosity. Depending on the heating conditions and the position of the samples during incorporation in the fusion devices, one can observe changes of the effusivity of the first surface layer to both lower and higher values.