Cavity Fabrication and Surface Preparation

Sustainability and cost reduction are key factors for the development of future large particle accelerators. This has led INFN LASA to start an INFN-funded R&D program dedicated to studying and improving the performance of SRF Nb cavities in terms of quality factor (High-Q) and accelerating gradient (High-G). Moreover, the R&D program is also pushed by the INFN LASA contribution to international projects such as PIP-II and by the participation on the international collaboration ILC Technology Network (ITN). The strategy of the R&D program consists of studying and optimizing different surface treatments on 1.3 GHz single-cell cavities that will later be applied to 9-cell cavities in view of the industrialization process needed for large scale production. A key activity of this program is the upgrade of our experimental vertical cold test facility needed to enable the qualification of such high-performance cavities. Ongoing activities include a new dedicated cryostat designed to minimize the liquid helium inventory consumption, the implementation of an active magnetic field compensation for the reduction of trapped magnetic flux, and the usage of a wide range of diagnostics for quench, field emission, etc. This paper presents the current status of the facility and its key features, an overview of cavities currently in production, and the experimental results obtained to date.

The ILC Technology Network (ITN) in Europe, in close collaboration with KEK and key institutions including CEA, CERN, INFN, is actively driving the development of advanced superconducting radiofrequency (SRF) technologies to support the realization of the International Linear Collider (ILC). The ITN-EU initiative focuses on developing and validating cost-effective, high-performance cavity production processes, transitioning from single-cell R&D to the industrialization of 9-cell cavities. Activities include optimizing surface treatment protocols, rigorous quality control of niobium materials, harmonization with Japanese High Pressure Gas Safety (HPGS) regulations, and preparing technical specifications for cavity jacketing and testing. As part of this program, Europe will contribute fully qualified SRF cavities to a globally designed ILC-type cryomodule for testing at KEK. The collaboration fosters knowledge exchange across laboratories and industry, supports advanced diagnostics development, and benefits from wider initiatives such as the Marie Skłodowska-Curie EAJADE network. These collective efforts not only support ILC realization but also reinforce Europe's strategic capabilities in SRF technology for future accelerators.

This contribution outlines the current status and recent progresses of INFN LASA’s in-kind contribution to the PIP-II project at Fermilab. It focuses on key manufacturing activities, on preliminary inspection results on sub-components and on upgrades to cavity testing infrastructures. The production of the 38, 5-cell, β = 0.61 SRF cavities designed by INFN LASA for the LB650 section of the linac is underway, starting with two pre-series units aimed at validating the full manufacturing and processing workflow. The series production is being carried out by industry, with cavities also undergoing most of surface treatments as well as final cleaning and preparation at vendor’s premises. Final experimental qualification, to verify that cavities meet the challenging performance specifications required by the project, will be conducted through vertical cold tests at the DESY AMTF (Germany) facility before being delivered at CEA Saclay (France) as ready for string-assembly.

INFN-LASA has successfully completed its in-kind contribution to the European Spallation Source Eric, delivering 36 superconducting medium beta cavities for the ESS Linac. These cavities are designed to increase the energy of the proton beam from 216 MeV to 571 MeV. In addition, four spare cavities are being fabricated. This article outlines the performance of the cavities delivered so far and updates on the production status of the latest cavities.

Minimizing residual magnetic fields during SRF cavity cooldown is essential for reducing surface resistance and improving the quality factor. At LASA-INFN, we implemented an active compensation system using Helmholtz-like coils in vertical test cryostats. The setup is optimized to reduce the average magnetic flux through the cavity surface by accounting for the spatial inhomogeneity of the residual field. Experimental studies on PIP-II prototype cavities confirm the critical role of magnetic field conditions during cooldown. Observations suggest that, if a quench occurs in the presence of such external fields, trapped flux can cause a lasting degradation of the quality factor.