LNL heavy ion accelerator complex is based on three main accelerators: Tandem, ALPI and PIAVE. The Tandem XTU is a Van de Graaff accelerator normally operated at terminal voltages of up to about 14 MV. It can be operated in stand–alone mode or as an injector for the linac booster ALPI. The linear accelerator ALPI is built of superconducting resonant cavities and consists of a low–beta branch, particularly important for the acceleration of the heavier mass ions, a medium–beta branch, and a high–beta branch. ALPI can be operated also with the PIAVE injector that consists of a superconducting RFQ and an ECR source. In the last two years, accelerator complex underwent special maintenance to improve its availability and reliability in view of the operation with both Uranium and radioactive beams. In this framework, the main improvements that will be presented will concern Tandem injector and laddertron system, PIAVE ECR source, cryogenic control system and SRFQ tuning system, ALPI low and medium beta design, vacuum control system and new techniques for beam dynamic simulation and commissioning.

Nb3Sn on Nb thin films cavities by Tin Vapor Diffusion already show performance at 4.2 K comparable to Nb bulk cavities at 2 K, but a real breakthrough would be the use of copper (instead of Nb) as substrate, to enhance the thermal conductivity, opening up the possibility to cool down the cavity using cryocoolers instead of the more expensive helium bath. Magnetron sputtering is the most studied technology for this purpose, however coating substrates with complex geometry (such as elliptical cavities) may require targets with non-planar shape, difficult to achieve with classic powder sintering techniques due to the brittleness of Nb3Sn. In this work, carried out within the iFAST collaboration, the possibility of using the Liquid Tin Diffusion (LTD) technique to produce sputtering targets for 6 GHz elliptical cavities is explored. The LTD technique is a wire fabrication technology, already developed in the past at LNL for SRF applications, that allows the deposition of very thick and uniform coating on Nb substrates even with complex geometry. Improvements in LTD process, proof of concept of a single use LTD target production, and characterization of the Nb3Sn film coated by DC magnetron sputtering with these innovative targets are reported in this work.

Superconducting radio frequency (SRF) cavities performances strongly depend on the surface preparation. Conventional protocol of SRF surface preparation includes electropolishing (EP) as the main treatment achieving low roughness, clean surface, both for Nb and Cu substrates. Harsh and corrosive solutions are typically used: concentrated HF and H2SO4 acids for Nb, and H3PO4 with Butanol mixtures for Cu. The application of PEP can be not only used for conventional elliptical resonators, but also for normal conducting cavities and other components of accelerators where polishing is normally applied, such as couplers. PEP is an evolution of EP with a list of advantages. Only diluted salt solutions are used, unlike EP. PEP can in principle substitute, or eliminate, intermediate steps, like mechanical and/or (electro) chemical polishing, thanks to superior removing rate in the field (up to 3.5 μm/min of Nb, and 10 μm/min of Cu). A ≤100 nm roughness achieved both for Nb and Cu substrates. A higher smoothing/polishing effect respect to an EP was obtained. PEP application onto the SRF substrates is shown. Defects evaluation of the substrate has been analysed.