Determining the Thermal Properties of Insulating Material Intended for Steering Plasma Beams

In order to determine the thermal properties of three different types of insulating material intended for use in steering plasma beams in nuclear fusion reactors, flash diffusivity tests were conducted at the Oak Ridge National Laboratory. Using a thermal camera, the temperatures on the non-heated side of the samples were measured over time. Because of the irregular shape of the samples, the traditional flash diffusivity analysis would not yield accurate results. Therefore, three-dimensional numerical models were generated for each sample. The temperature histories that resulted from the flash diffusivity tests were then fitted by employing the three-dimensional models generated using ANSYS. Various models involving convective and radiative heat losses from the sample surfaces were compared, including a model accounting for penetration of the flash beyond the surface of the semi-porous materials. A significant improvement in the standard deviation of the residuals resulted from the application of the models which accounted for convection and flash penetration. The differences in the resulting thermal diffusivity values ranged from 17 percent to 46 percent from the values obtained using the traditional Parker analysis method for the three types of materials. Plots of the residuals are included to show the improvements gained by the use of the higher-order models.