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

• Published in: AIP advances Vol. 7; no. 12; pp. 125016 - 125016-5
• Main Authors: Upadhyay, J., Palczewski, A., Popović, S., Valente-Feliciano, A.-M., Im, Do, Phillips, H. L., Vušković, L.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 01.12.2017; American Institute of Physics (AIP); AIP Publishing LLC
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Chemical elements; Chlorine; Cryogenic engineering; Cryogenic temperature; Cryogenics; Discharge; Electrical properties and parameters; Electrodes; Emission analysis; Etching; Field emission; Gas flow; High temperature; Holes; Ion etching; Organic chemistry; Physics of gases; Plasma etching; Plasma processing; Reactive ion etching; Superconductivity; Surface collisions; Transition metals; Vacuum apparatus
• ISSN: 2158-3226; 2158-3226
• DOI: 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.