A Polishing Procedure for High Surface Electric Fields in Superconducting Lead Resonators

A chemical polishing procedure has been developed which allows fields of 20-30 MV/m to be routinely achieved at the surfaces of superconducting resonators constructed of lead-plated copper. This has made possible the construction of lead plated resonators with accelerating fields equivalent to those achieved with niobium, since the performance of these resonators is limited by electric field breakdown.
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The polish itself is based on a weak acidic solution of hydrogen peroxide and EDTA, a chelating agent. Other polishes have not proven suitable for the thin (5-10μ) lead layer because of their very high polishing rates. The present procedure, however, gives good polishing action even at rates as slow as 5μ/min. Details of the procedure as well as comparative electric field breakdown data are presented.