2024 AIChE Annual Meeting
Topographic Analysis of Niobium during Incremental Electropolishing
Superconducting radio frequency (SRF) niobium cavities are pivotal for experimentation at Thomas Jefferson National Accelerator Facility (TJNAF). The peak electromagnetic fields achievable in these cavities depend on the smoothness of the surface. At high accelerating fields, topographic defects may create opportunities for excessive dissipation and thermal runaway turning the cavity normal conducting. Scientists at TJNAF place immense emphasis on preparing and analyzing niobium samples for optimization, as well as improving methods of analysis. The effect of electropolishing on surface defects was investigated via atomic force microscopy. Relevant parameters were analyzed from the topographic data for the maximum accelerating field in Nb cavities. Magnetic field enhancement (MFE) and superheating field suppression (SFS) factors of the surface were calculated to develop a deeper understanding of the effect of electropolishing on irregular defects in polished Nb. Via incremental EP of Nb, there was an overall decrease in the depth of the groove and MFE. It would be of interest to develop a model for estimating the change in shape of irregular topographic defects with EP. Nb3Sn hosts areas of high slope angles and groove depths, and next steps involve applying a polishing technique to ameliorate these locations. This comparative analysis of Nb will assist in estimating the amount of material needed to be removed from the sample surface of cavity materials to eliminate negative impact on high field performance. Such a model may be useful for next generation SRF cavity material.