• A.T. Wu, G. Ciovati, R. Manus, H.L. Phillips, C.E. Reece, R.A. Rimmer, W. Sommer, H. Tian, J.S. Williams
  JLAB, Newport News, Virginia
• F. Eozénou
  CEA, Gif-sur-Yvette
• S. Jin, L. Lin, X.Y. Lu, E. Wang
  PKU/IHIP, Beijing
• J. Mammosser
  ORNL, Oak Ridge, Tennessee

Funding: Notice: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

A new surface treatment technique for niobium (Nb) Superconducting Radio Frequency (SRF) cavities called Buffered Electropolishing (BEP) has been developed at JLab. It was found that BEP could produce the smoothest surface finish on Nb samples ever reported in the literature. Experimental results revealed that the Nb removal rate of BEP could reach as high as 4.67 μm/min. This is significantly faster* than that of the conventional electropolishing technique employing an acid mixture of HF and H2SO4. An investigation is underway to determine the optimum values for all relevant BEP parameters so that the high quality of surface finish achieved on samples can be realized within the geometry of an elliptical RF cavity. Toward this end, single cell Nb cavities are being electropolished by BEP at both CEA-Saclay and JLAB. These cavities will be RF tested and the results will be reported through this presentation.

*Xiangyang Lu et al, to be published.

• B. Xiao, R.L. Geng, F. Marhauser, H.L. Phillips, C.E. Reece, H. Wang
  JLAB, Newport News, Virginia
• M.J. Kelley
  The College of William and Mary, Williamsburg

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.

Much remains to be learned regarding the details of SRF performance effects with material variation, including niobium treated in different ways, and different bulk/thin film materials that are fabricated under different conditions. A facility that can measure small samples’ RF properties in a range of 0~180mT magnetic field and 2~20k temperature is necessary in order to answer this question. The Jefferson Lab surface impedance characterization (SIC) system has been designed to attempt to meet this requirement. The SIC system uses a sapphire-loaded cylindrical Nb cavity at 7.5GHz with 50mm diameter flat sample placed on a non-contacting end plate and a calorimetric technique to directly measure the rf dissipation in the sample in response to known rf fields over ~1 cm². We report on the commissioning of this system and its first uses for characterizing materials. Preliminary tests with Nb thin film sample sputtered on Cu substrate, and bulk Nb sample have been done at low field. The presently available hardware is expected to enable tests up to 20 mT peak magnetic field on the sample CW. Paths to higher field tests have been identified.