RF surface resistance of copper-on-beryllium at cryogenic temperatures measured by a 22-GHz demountable cavity

A 22-GHz demountable cavity on the cold head of a compact refrigerator system was used to measure the RF performance of several copper-plated Beryllium samples. The cavity inner surface was treated by chemical polishing and heat treatment, as well as an OFE copper coupon to provide a baseline for comparison. The measured surface resistance was reasonable and repeatable during either cooling or warming. Materials tested included four grades of Beryllium, OFE copper, alumina-dispersion strengthened copper (Glidcop®), and Cu-plated versions of all of the above. Two coupons, Cu-plated on Beryllium O-30 and 1-70, offered comparable surface resistance to pure OFE copper or Cu-plated Glidcop. The RF surface resistance of Cu-on-Beryllium samples at cryogenic temperatures is reported together with that of other reference materials.