Effect of cathode shape on vertical buffered electropolishing for niobium SRF cavities

•Investigation of vertical macro-electropolishing for superconducting RF cavities is reported.•A unique JLab home-made demountable single cell Nb cavity is used in the investigation.•This study demonstrates that cathode shape has dominant effects on the surface finish of Nb SRF cavities treated by BEP.•The conventional EP is found to show the same tendency.•BEP shows advantages in roughness and polishing rate comparing with those of EP.