Design and development of an emissivity measurement set-up for use at 100 K

For the best performance of the Activated carbon based cryopumps, the activated carbon should be at the lowest possible temperature. For this, the heat load from the surroundings has to be minimized. Radiation heat load is significant and depends on the emissivity of surfaces. Since the emissivity data are scarce at cryogenic temperatures, we have developed an experimental setup based on the calorimetric method for the measurement of emissivity of various coatings or parts at these temperatures around 100 K. The setup consists of a heater located inside a vacuum vessel at 77K. When the heat transfer between the heater and the receiving surface is nearly by radiation, using the measurements of heat load and the temperatures, the emissivities of the different surfaces can be estimated. The design and fabrication of the experimental setup along with the preliminary results are presented in this paper.