JLAB, Newport News, Virginia
The College of William and Mary, Williamsburg
As the field requirements of niobium SRF cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. In this study, a set of samples representing 24 different starting conditions used in cavity processing has been assembled. This set includes fine grain, large grain, and single crystal Nb samples under EBW’ed, hand ground, and CBP with a variety of stones, the latter provided by KEK colleagues. Sample topography has been carefully characterized in both the initial condition and after removal of 30 microns via controlled-parameter EP. A power spectral density (PSD) approach based on Fourier analysis of surface topography*, stylus profilometry and atomic force microscopy (AFM) are used to distinguish the scale-dependent smoothing effects. The detailed topographic transformation of Nb surface with the varied starting state Nb surface (CBP/ EBW) is reported. This study will help to identify optimum EP parameter sets for controlled and reproducible surface leveling of Nb for cavity production.
* “Surface Roughness Characterization of Niobium Subjected to Incremental BCP and EP Processing Steps” , Hui Tian, G. Ribeill, Charles E. Reece, and Michael J. Kelley. Proceedings of SRF2007.
