Nb3Sn Targets Synthesis via Liquid Tin Diffusion for Thin Films Depositions

The deposition of superconducting Nb3 Sn on copper accelerating cavities is interesting for the higher thermal conductivity of copper compared to common Nb substrates. The better heat exchange would allow the use of cryocoolers reducing cryogenic costs and the risk of thermal quench [1]. The magnetron sputtering technology allows the deposition of Nb 3 Sn on substrates different than Nb, however the coating of substrates with complex geometry (such as elliptical cavities) may require target with non-planar shape, which are difficult to realize with classic powder sintering techniques. In this work, the possibility of using the Liquid Tin Diffusion (LTD) technique to produce sputtering targets is explored. The LTD technique is a wire fabrication technology, already developed in the past at LNL for superconducting radio frequency (SRF) applications [2], that allows the deposition of very thick and uniform coating on Nb substrates even with complex geometries [3]. Improvements in LTD process, proof of concept of a single use LTD target production, and characterization of the Nb 3 Sn film coated by DC magnetron sputtering with these innovative targets are reported in this work

STUDIO E SVILUPPO DELLE TECNICHE DI DEPOSIZIONE DI FILM SOTTILI DI Nb3Sn PER APPLICAZIONI IN CAVITAâ RISONANTI

La fisica delle particelle si sta spingendo verso l’esplorare range di energia sempre più elevati, che richiedono strutture acceleranti sempre più performanti per essere sostenibili. Le performance delle cavità acceleratrici in Nb bulk attualmente hanno ormai raggiunto i limiti teorici imposti dal materiale stesso e risulta pertanto necessario guardare ad altri materiali superconduttori, tra i quali il più promettente è il Nb3Sn. Un superconduttore è caratterizzato dalla temperatura critica (Tc) sotto la quale esibisce resistenza elettrica nulla. In radiofrequenza sussistono ugualmente delle perdite dovute alla resistenza superficiale. Il Nb3Sn comporta una temperatura di esercizio di 18K doppia rispetto al Nb, questa caratteristica riduce la resistenza superficiale, consentendo l’aumento del campo accelerante massimo oltre a diminuire i costi criogenici. L’alto campo magnetico critico di 24T rende inoltre questo superconduttore adatto all’applicazione in cavità per la rilevazione di assioni. In questo lavoro è adottata la tecnica denominata Liquid Tin Dipping (LTD) per la creazione di film spessi di Nb3Sn su substrati di Nb a geometria complessa. Lo scopo principale del lavoro è la realizzazione di target per deposizioni di Nb3Sn via Magnetron Sputtering in cavità di rame a geometria ellittica. Data la flessibilità della tecnica, l’LTD è stata anche ottimizzata per il futuro ricoprimento della cavità per assioni. Metodologie di processo differenti sono state indagate per minimizzare le fasi indesiderate e per aumentare lo spessore finale del film (parametro critico in un target). Si è studiato l’effetto del tempo di dipping e del tempo di annealing, sviluppando un processo a più cicli (in presenza e/o assenza di vapori di stagno) per regolare la quantità media di Sn e variare i rapporti tra le fasi ottenute. Infine, è stata verificata l’efficacia di pretrattamenti di anodizzazione, già utilizzati nel processo Siemens (crescita di Nb3Sn per diffusione di stagno da fase vapore), nel favorire la nucleazione, producendo un film della fase desiderata più uniforme lungo tutta la superficie del campione. Ogni metodologia o variazione del processo è studiata mediante caratterizzazioni SEM, EDS e diffrattometria XRD; queste hanno permesso di valutare come le variabili di processo influiscano sulle caratteristiche finali del coating. Le analisi svolte dimostrano come è possibile ottenere film stechiometrici di Nb3Sn, privi di fasi spurie, partendo da substrati di Nb pre-anodizzati e rivestendoli mediante la metodologia ibrida, che prevede una doppio annealing in situ dopo il processo di dipping: un primo annealing in presenza di vapori di stagno, ed un successivo annealing in ultra alto vuoto

Nb3Sn Targets Synthesis via Liquid Tin Diffusion for Thin Films Depositions

The deposition of superconducting Nb3 Sn on copper accelerating cavities is interesting for the higher thermal conductivity of copper compared to common Nb substrates. The better heat exchange would allow the use of cryocoolers reducing cryogenic costs and the risk of thermal quench [1]. The magnetron sputtering technology allows the deposition of Nb 3 Sn on substrates different than Nb, however the coating of substrates with complex geometry (such as elliptical cavities) may require target with non-planar shape, which are difficult to realize with classic powder sintering techniques. In this work, the possibility of using the Liquid Tin Diffusion (LTD) technique to produce sputtering targets is explored. The LTD technique is a wire fabrication technology, already developed in the past at LNL for superconducting radio frequency (SRF) applications [2], that allows the deposition of very thick and uniform coating on Nb substrates even with complex geometries [3]. Improvements in LTD process, proof of concept of a single use LTD target production, and characterization of the Nb 3 Sn film coated by DC magnetron sputtering with these innovative targets are reported in this work

Nb3Sn Targets Synthesis via Liquid Tin Diffusion for Thin Films Depositions

The deposition of superconducting Nb3 Sn on copper accelerating cavities is interesting for the higher thermal conductivity of copper compared to common Nb substrates. The better heat exchange would allow the use of cryocoolers reducing cryogenic costs and the risk of thermal quench [1]. The magnetron sputtering technology allows the deposition of Nb 3 Sn on substrates different than Nb, however the coating of substrates with complex geometry (such as elliptical cavities) may require target with non-planar shape, which are difficult to realize with classic powder sintering techniques. In this work, the possibility of using the Liquid Tin Diffusion (LTD) technique to produce sputtering targets is explored. The LTD technique is a wire fabrication technology, already developed in the past at LNL for superconducting radio frequency (SRF) applications [2], that allows the deposition of very thick and uniform coating on Nb substrates even with complex geometries [3]. Improvements in LTD process, proof of concept of a single use LTD target production, and characterization of the Nb 3 Sn film coated by DC magnetron sputtering with these innovative targets are reported in this work

Thick Film Morphology and SC Characterizations of 6 GHz Nb/Cu Cavities

Thick films deposited in long pulse DCMS mode onto 6 GHz copper cavities have demonstrated the mitigation of the Q-slope at low accelerating fields. The Nb thick films (~40 microns) show the possibility to reproduce the bulk niobium superconducting properties and morpholo-gy characterizations exhibited dense and void-free films that are encouraging for the scaling of the process to 1.3 GHz cavities. In this work a full characterization of thick films by DC magnetometry, computer tomography, SEM and RF characterizations are presented

Machine perfusions in liver transplantation: The evidence-based position paper of the italian society of organ and tissue transplantation.

BACKGROUND AND AIMS The use of machine perfusion in liver transplantation is spreading worldwide but its efficacy has not been demonstrated and its proper clinical use far to be implemented. The Italian Society of Organ and Tissue Transplantation (SITO) promoted the development of an evidence-based position paper. METHODS A three-step approach has been adopted to develop this position paper. Firstly, the Society appointed a Chair and a co-Chair who then assembled a Working Group with specific experience of machine perfusion in liver transplantation. The Guideline Development Group framed the clinical questions into a Patient/Intervention/Control/Outcome (PICO) format, extracted and analyzed available literature, ranked the quality of evidence, prepared and graded the recommendations. Recommendations were then discussed by all the members of the SITO and voted by Delphi round by an Internal Review Board and finally evaluated and scored by a panel of external reviewers. RESULTS All available literature was analyzed, and its quality ranked. Eighteen recommendations regarding the use and the efficacy of ex-situ hypothermic and normothermic machine perfusion and sequential normothermic regional perfusion and ex-situ machine perfusion were prepared and graded according to the GRADE method. CONCLUSION A critical and scientific approach is required for the safe implementation of this new technology