The main goals driving the development of future accelerators are to lower the power losses (by increasing the quality factor Q0 – Ploss ∝ 1/Q0) and increase the accelerating field (Eacc) in a reproducible way, to contain both capital and operational costs of future accelerators. Niobium (Nb) is widely recognized as the reference for bulk superconducting material of accelerating cavities, providing extremely high accelerating gradients with small losses (few Watts per cavity at 2 K). To increase Q0 and Eacc, R&D efforts are pursued on Nb material: surface polishing with High Pressure Rinse (HPR), Buffered Chemical Polishing (BCP), ElectroPolishing (EP), surface treatment (Nitrogen doping and infusion) and heat treatments (low/mid/2-step baking, Hydrogen degassing).
In addition to pushing the limits of cavity performances, it is essential to confirm them in large series production by industry and to maintain them over time. Reproducibility is enabled by both reducing contamination during assembly, e.g. via cobots in clean room, and recovering from field emission with in-situ plasma processing.
