Anisotropic thermal conductivity of hydrogen deuteride crystal for polarized proton target development

The thermal conductivity of a hydrogen deuteride (HD) single crystal is measured at 3-7 K for two mutually perpendicular directions of heat flow in the crystal. The HD sample is prepared by direct crystallization from ultra high-purity HD gas. A typical anisotropy with a ratio of nearly tenfold is obtained for the thermal conductivity in the measured temperature region. Approximate calculations of the anisotropic thermal conductivity in the HD crystal are performed using an analytical formulation of the two-dimensional anisotropic heat conduction, while taking into account cross-plane coupling of phonon Umklapp scattering. The approximate calculations are found to be in reasonable agreement with the experimental results.