State of the Art of Niobium Machining for SRF Applications

Niobium is a demanding material to be machined. Its low hardness, high melting temperature and abrasivity leads to poor cutting condition, and surface quality and shape accuracy could be difficult to achieve, especially for complex shapes such as HOM antennas. Recent CERN developements concerning DQW crab cavity for HL-LHC project had implied extensive research program to better understand and master the machining of this material. In this frame, the present article will introduce actual state of the art machining condition used at CERN and their consequences about the surface roughness, shape accuracy and taking into account the tool wear in order to maintain this level of quality. Morevoer, advance machning solution, such as cryogenic cooling could be used.