Steady-State Method to Measure the In-Plane Thermal Conductivity of Thin Sheet Materials*

A new generation of silicon pixel detectors is required to cope with the unprecedented luminosities at the high-luminosity phase of the Large Hadron Collider (HL-LHC) in 2025. The HL-LHC will provide a high radiation and interaction rate environment for the innermost detector region of the Compact Muon Solenoid (CMS) detector. To address this challenge, the spatial coverage of the inner silicon detector will be increased while also decreasing the size of a pixel. This increases the number of readout channels significantly, which produces more heat compared to existing pixel devices. Therefore, the Phase II upgrade to the CMS experiment requires an improved light-weight heat removal scheme, which is addressed by using carbon fiber as one of the materials for the silicon detector support structure. To simulate and optimize the performance of this support structure, knowing the thermal conductivity is crucial. Because thermal conductivity of carbon fiber is anisotropic, measurements along and perpendicular to the fibers are performed separately. In-plane thermal conductivity measurements of several thin in-house cured carbon fiber sheets are performed. We measure the thermal conductivity of Carbon Fiber K13D2U/TC275-1 in the plane and along the fiber to be 515 ± 72 W/mK.