Cryogenic rf test of the first SRF cavity etched in an rf Ar/Cl2 plasma

• Main Authors: J. Upadhyay, A. Palczewski, S. Popović, A.-M. Valente-Feliciano, Do Im, H. L. Phillips, L. Vušković
• Format: Article
• Language: English
• Published: AIP Publishing LLC 2017-12-01
• Series: AIP Advances
• Online Access: http://dx.doi.org/10.1063/1.4991888

An apparatus and a method for etching of the inner surfaces of superconducting radio frequency (SRF) accelerator cavities are described. The apparatus is based on the reactive ion etching performed in an Ar/Cl2 cylindrical capacitive discharge with reversed asymmetry. To test the effect of the plasma etching on the cavity rf performance, a 1497 MHz single cell SRF cavity was used. The single cell cavity was mechanically polished and buffer chemically etched and then rf tested at cryogenic temperatures to provide a baseline characterization. The cavity’s inner wall was then exposed to the capacitive discharge in a mixture of Argon and Chlorine. The inner wall acted as the grounded electrode, while kept at elevated temperature. The processing was accomplished by axially moving the dc-biased, corrugated inner electrode and the gas flow inlet in a step-wise manner to establish a sequence of longitudinally segmented discharges. The cavity was then tested in a standard vertical test stand at cryogenic temperatures. The rf tests and surface condition results, including the electron field emission elimination, are presented.