Surface treatments play a crucial role in applied physics, particularly in fields demanding exceptional cleanliness, polishing, and surface modification to meet the stringent requirements of modern experimental science. Superconducting RF (SRF) accelerators, developed over the past 60 years, have driven advancements in the treatment of superconducting materials, requiring ultra-smooth surfaces, high-purity (300 RRR) niobium, uniform material removal of 150–200 µm, and controlled grain crystallinity. Currently, standard chemical treatments rely on highly concentrated and toxic acids, with few viable alternatives.
An alternative approach—coating superconducting (SC) films onto alternative substrates, such as copper—has been successfully demonstrated in accelerators like ALPI, LEP-II, LHC, and ISOLDE. Meanwhile, as bulk niobium technology nears its physical limits, the field is shifting toward promising new materials such as A15 compounds like Nb₃Sn, which offers a higher critical temperature (18.3 K) and enables operation at 4.5 K instead of 2 K. This transition makes substrate preparation a critical challenge in achieving reproducible and reliable SRF cavity performance.
The expertise developed in the SRF field over the years has also enabled advancements in other sectors. One emerging area is quantum science, particularly the development of SC cavities for qubits and quantum memories within the PNRR NQSTI initiative. This synergy has already led to a significant improvement in the Q factor of aluminium cavities, from 10⁵ to 10⁶, with further strategies yet to be explored. Additionally, advancements in surface treatments could benefit astroparticle physics experiments, such as DarkSide and CUORE/CUPID, where ultra-clean, highly polished surfaces are crucial for minimising background contamination.
This seminar will highlight the importance of surface treatments and the continuous contributions of INFN-LNL in advancing these technologies. Particular attention will be given to the emerging demand for polishing additively manufactured (AM) components. A focus will be placed on the optimisation, development, and application of innovative surface treatments, with a special emphasis on Plasma Electrolytic Polishing (PEP). LNL is currently a global leader in PEP research and development, holding three PCT patents for its application on copper and niobium. The seminar will provide an overview of the technology readiness level (TRL) progression of PEP for 1.3 GHz SRF cavities, as well as strategies for scaling the process to even larger geometries, such as 400 MHz cavities.
Pierfrancesco Mastinu