Study of the role of the interface between niobium films and copper RF resonators

Niobium-coated copper resonators are usually produced with an oxide interface between the film and the substrate. This oxide has two sources: the passivation layer inevitably formed on the surface of the cavity after chemical preparation before coating, and the niobium oxide which builds up on the surface of the cathode when it is exposed to air, and is transferred to the cavity surface during coa ting. The oxide layer may influence both the purity and the structural properties of the film, and in turn its RF behaviour. To study its effect, some cavities have been coated with a special two-cath ode sputtering system, allowing for a complete removal of both oxide layers by sputter-etching. For comparison, a few cavities have also been produced with the same coating system without sputter-etch ing, or with a controlled oxidation of the copper surface of the cavity after sputter-etching. Two cavities have also been produced without oxide interface using Kr and Ne as sputter gas instead of Ar

Ferrite-damped higher-order mode study in the Brookhaven energy-recovery linac cavity

A superconducting energy-recovery linac (ERL) is under construction at Brookhaven National Laboratory (BNL) to serve as a test bed for an application to upgrades of the Relativistic Heavy Ion Collider (RHIC). The damping of higher-order modes in the superconducting five-cell cavity is of paramount importance and represents the topic of this paper. Achieving the damping by the exclusive use of two ferrite absorbers and the adoption of a space-saving step instead of the conventional taper are part of the exploratory study. Absorber properties which are portable to simulation programs for the ERL cavity have been obtained by measuring the absorber as a ferrite-loaded pill-box cavity. Measured and simulated results for the lowest dipole modes in the prototype copper cavity with one absorber are discussed. First room-temperature measurements of the fully assembled niobium cavity string are presented which confirm the effective damping of higher-order modes by the ferrite absorbers, and which give credibility to the simulated R over Q's in the ERL.open1

Study of the surface resistance of superconducting niobium films at 1.5 GHz

A systematic study of superconducting properties of niobium films sputtered on the inner wall of radiofrequency cavities is presented. The measured quantities include in particular the response to 1.5 GHz microwaves, the critical temperature, the penetration depth and the magnetic penetration field. In addition to films grown in different gas discharges (Xe, Kr, Ar and Ar/Ne mixtures) and to films grown on substrates prepared under different conditions, the study also includes bulk niobium cavities. The surface resistance is analysed in terms of its dependence on temperature, on RF field and, when relevant, on the density of trapped fluxons. A simple parameterisation is found to give a good fit to the data. Once allowance for the presence of impurities and defects is made by means of a single parameter, the electron mean free path, good agreement with BCS theory is observed. The fluxon-induced losses are studied in detail and their dependence on RF field, on temperature and on the density of trapped fluxons is analysed. The residual resistance is observed to be essentially uncorrelated with the other variables, suggesting that it is dominantly extragranular. In occasions very low residual resistances, in the n Omega range, have been maintained over a broad range of RF field, indicating the absence of significant fundamental limitations specific to the film technology in practical applications such as the production of accelerating cavities for particle accelerators. (130 refs)

Properties of Copper Cavities Coated with Niobium Using Different Discharge Gases

Experimental evidence is presented showing that in conformity with theoretical expectations, discharge gas atoms are trapped in sputtered films whenever a gas of atomic mass smaller than that of the c athode is used. In such a case, discharge gas atoms may be reflected by the cathode as high energy neutrals and get incorporated in the growing film. Niobium films have been produced using Ne, Ar, Kr, Xe and then analysed for rare gas content by thermal extraction. The gas concentrations are found to vary from the several percent range for Ne down to the ppm level for Kr and Xe. The noble gas conce ntration in the film influences the RRR and, in the case of high concentration, also the critical temperature. To study the effect of the implanted noble gas on the superconducting RF parameters, seve ral 1.5 GHz copper cavities have been niobium-coated using the different discharge gases. The noble gases trapped in the film affect the penetration depth, the temperature dependent losses (RBCS), the losses induced by the presence of trapped fluxons, but have no significant influence on the residual resistance

Magnetic flux trapping in superconducting niobium

In a systematic study of the RF response of superconducting niobium cavities operated in their fundamental TM010 mode at 1.5 GHz, magnetic flux trapping has been used as a tool to diagnose the presenc e of pinning centres. In addition to bulk niobium cavities the study covers copper cavities, the inner walls of which are coated with 1.5 µm thick niobium films grown by magnetron sputtering in a nobl e gas atmosphere. The use of different gases (Xe, Kr, Ar and Ne) or gas mixtures has made it possible to vary the concentration of noble gas atoms in the films. Film contamination is characterised by an electron mean free path l calculated from the results of systematic measurements of the penetration depth at T = 0 K, l0, and from RRR measurements made on samples prepared under similar conditions as the cavity films

Un anno di Comitato Unico di Garanzia: riflessioni all'INGV

L’Istituto Nazionale di Geofisica e Vulcanologia - INGV ha istituito il Comitato Unico di Garanzia per le pari opportunità, la valorizzazione del benessere di chi lavora e contro le discriminazioni – CUG nel luglio 2011, ai sensi della L.183/2010. Il CUG ha assunto, estendendoli, i compiti del precedente Comitato Pari Opportunità, ossia, come da delibera CD n.4.3.2.11 del 28/6/2011: • focalizzare i problemi relativi alle pari opportunità; • contribuire a migliorare la qualità della vita negli ambienti di lavoro e a valorizzare le risorse umane; • verificare gli equilibri tra i sessi nelle posizioni funzionali a parità di requisiti professionali; • formulare proposte per: la gestione flessibile delle risorse umane e le attività di formazione professionale; è inoltre chiamato a perseguire gli obiettivi della direttiva dei dipartimenti della Funzione Pubblica e per le Pari Opportunità del 4 marzo 2011, per esercitare compiti propositivi, consultivi e di verifica. I compiti affidati dall’Amministrazione da un lato e le sollecitazioni ricevute dal personale dall’altro hanno portato ad una serie di azioni, tra le principali: • la redazione di un Codice per la tutela della dignità delle persone e per la prevenzione delle molestie sessuali e morali dell’INGV, l’individuazione della Consigliera di Fiducia e l’avvio di un ciclo di seminari sull’argomento, nell’ambito della prevenzione delle discriminazioni; • una lettura di genere delle bozze dei nuovi regolamenti dell’ente, con proposte di modifiche ispirate alla Carta Europea dei Ricercatori – CdR (e.g. principi di Non discriminazione, Equilibrio di genere) e alla normativa in tema di pari opportunità e tutela della maternità, parte delle quali recepite nel Regolamento del Personale e nel Disciplinare in materia di orario di servizio; un’azione, questa, legata all’adesione in via sperimentale alla Human Resources Strategy for Researchers, iniziativa della Comunità Europea per l’effettiva implementazione della CdR; • nell’ambito del processo di valutazione della ricerca dell’ANVUR, l’evidenziazione di alcune criticità presenti nel bando, in relazione alla valutazione della maternità, risultate in una interrogazione parlamentare e in una lettera aperta, grazie al contributo dell’Associazione Donne e Scienza e dei CUG dell’INFN e del CNR. Le esperienze fatte confermano l’opportunità di dare voce a tutte le donne dell’Istituto e di fare rete tra i Comitati degli enti di ricerca.UnpublishedCertosa di Pontignano (Siena), Italyope

Structural and RF properties of niobium films deposited onto annealed niobium resonators

Studies have been performed on the properties of niobium thin films sputtered onto solid niobium TM010 resonators at 1.5 GHz. The purpose of the work is to study the behaviour of the film's RF and str uctural properties as a function of heat treatment temperature in order to determine if and at what treatment temperature the properties of the films merge with those of the bulk. Niobium resonators h ave been heat treated at temperatures up to 1100°C in a vacuum furnace inside a niobium box surrounded by a titanium gettering protection. Subsequently, they have been sputter coated with a niobium fi lm. Following RF measurements of the coated resonators, the cavities have undergone heat treatments as described above at 800°C, 900°C, 1000°C and 1100°C, each time followed by RF measurements. Before heat treatment, the RF response of the film was similar to that of a film coated on a copper substrate. A marked transition towards bulk-like RF behaviour was observed after the 900°C treatment. The c hanges include a sharp variation of the BCS resistance and of the sensitivity to externally applied magnetic field, quantities believed to be closely linked to the amount and nature of defects in the coating

Differences in Disease Severity but Similar Telomere Lengths in Genetic Subgroups of Patients with Telomerase and Shelterin Mutations

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited