Frequency Scaling from Copper to SC Niobium

The linac of HIE-ISOLDE Project is based on two gap independently phased Quarter Wave Resonators (QWRs). The cavities are made in bulk Copper and subsequently Niobium sputtered. The working frequency in superconducting mode of operation is 101.28MHz at 4.5K. The purpose of this paper is to properly evaluate the scaled frequency of the Copper cavity at room temperature in air, in order to guide all the necessary steps in the production phase before going to the cryostat.