Nb thick films in 6 GHz superconducting resonant cavities

A key challenge for the next accelerators is the cost reduction. Bulk niobium cavities performances are closer to their theoretical limits and an alternative technology is mandatory. Niobium thin film copper cavities are the most explored solution, but the Q-slope characteristic of these resonators limits the applications where high accelerating fields are requested. In this work an original approach is adopted in order to enhance the performances of sputtered cavities, exploring the possibility to sputter 70 micron thick films to straighten up the Q-slope in Niobium sputtered copper cavities. The engineering of Nb thick films deposition on 6 GHz copper cavities, necessary to minimize the stress on niobium thick films and avoid film peeling from the substrate, is reported. Thick films show RRR values over 60. Different strategies have been used for stress reduction: deposition at high temperature of 550 °C, deposition at the zero stress pressure point (5∙10-2 mbar), and the development of a multilayer deposition procedure. Rf tests at 4,2 K and 1,8 K on 6 GHz resonant cavities are the tool used to evaluate the influence of the critical deposition parameters on the cavity performances. Two different venting procedures have been tested: a standard one, and a high temperature one, in which pure nitrogen is inserted in the vacuum chamber immediately after the end of the sputtering process. Thick films open the possibility to post treatments on sputtered cavities: the effect of buffer chemical polishing and heat treatments at different temperature have been investigated. The Rf tests on 6 GHz cavities show the fundamental role played by the surface preparation and the possibility to enhance the maximum accelerating field minimizing the film stress. Above all, for the first time, the possibility to obtain flat curve of Q-factor versus accelerating field in sputtered cavities with thick films it is demonstrated

Nb superconductive thin film coating on flat Cu disks for high gradient applications

In this work we present the characterization of Nb superconductive films deposed on copper substrates with two different techniques: the PVD magnetron sputtering and the Pulsed Laser Ablation. In the first method Nb films ∼ 3µm thick were deposited with an average roughness of 160 nm. The superconductivity properties of these films were also determined with a 4-probe resistivity measurement. Data show a superconducting transition at 9.6K as expected from Nb films. With the second technique thick Nb films were deposited on copper substrates using the Pulsed Laser Ablation. In this case the Rutherford Backscattering was used to determine the thickness and the chemical state of these films that show different degrees of oxidation

Vortex-induced nonlinearity and the effects of ion irradiation on the high-frequency response of NbTi films

The microwave response of superconducting devices can be affected by nonlinearity effects of both intrinsic and extrinsic origin. In this study, we report on the nonlinear behavior of NbTi microwave resonators, in the presence of dc magnetic fields up to 4 T. The aim of this work is to characterize the vortex-induced nonlinearity, which in these conditions of frequency (11 GHz) and fields is expected to give the major contribution to dissipation, when the circulating rf current exceeds a given threshold. Nonlinearity is investigated by analyzing -degradation and resonance curve distortion as a function of the input rf power, while the emergence of sharp discontinuities is associated to the existence of an rf limiting current density. The current densities corresponding to the onset of these features are compared to the critical current density from dc measurements, helping us to outline a comprehensive picture. Moreover, the pinning constant was extracted as a function of temperature by means of a Gittleman–Rosenblum analysis, revealing the prominent role of type pinning. We also analyzed the effects of introducing controlled artificial disorder and pinning sites through 1.5-MeV proton irradiation. After irradiation, we observed an increase of both the pinning constant and the in-field nonlinearity threshold and limiting current

The commissioning of the CUORE experiment: the mini-tower run

CUORE is a ton-scale experiment approaching the data taking phase in Gran Sasso National Laboratory. Its primary goal is to search for the neutrinoless double-beta decay in 130Te using 988 crystals of tellurim dioxide. The crystals are operated as bolometers at about 10 mK taking advantage of one of the largest dilution cryostat ever built. Concluded in March 2016, the cryostat commissioning consisted in a sequence of cool down runs each one integrating new parts of the apparatus. The last run was performed with the fully configured cryostat and the thermal load at 4 K reached the impressive mass of about 14 tons. During that run the base temperature of 6.3 mK was reached and maintained for more than 70 days. An array of 8 crystals, called mini-tower, was used to check bolometers operation, readout electronics and DAQ. Results will be presented in terms of cooling power, electronic noise, energy resolution and preliminary background measurements

Results from the Cuore Experiment

The Cryogenic Underground Observatory for Rare Events (CUORE) is the first bolometric experiment searching for neutrinoless double beta decay that has been able to reach the 1-ton scale. The detector consists of an array of 988 TeO2 crystals arranged in a cylindrical compact structure of 19 towers, each of them made of 52 crystals. The construction of the experiment was completed in August 2016 and the data taking started in spring 2017 after a period of commissioning and tests. In this work we present the neutrinoless double beta decay results of CUORE from examining a total TeO2 exposure of 86.3kg yr, characterized by an effective energy resolution of 7.7 keV FWHM and a background in the region of interest of 0.014 counts/ (keV kg yr). In this physics run, CUORE placed a lower limit on the decay half- life of neutrinoless double beta decay of 130Te > 1.3.1025 yr (90% C. L.). Moreover, an analysis of the background of the experiment is presented as well as the measurement of the 130Te 2vo3p decay with a resulting half- life of T2 2. [7.9 :- 0.1 (stat.) :- 0.2 (syst.)] x 10(20) yr which is the most precise measurement of the half- life and compatible with previous results

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Investigation of a Possible Material-Saving Approach of Sputtering Techniques for Radiopharmaceutical Target Production

Magnetron sputtering (MS) is a relatively new deposition technique, which is being considered among the cyclotron solid target (CST) manufacturing options now available, aiming at the medical radioisotopes yield for radiopharmaceutical production. However, the intrinsic high material losses during the deposition process do not permit its use with extremely expensive target materials, such as isotopically enriched metals/oxides. In this study, R&D technology for a new recovering shield is instead proposed to assess the dissipation of target material during the sputtering processes and, thus, an estimate of the material recovery that may be feasible and the related amount. The weight-loss analysis method is used to assess the material losses level inside the chamber during processing. In all tests carried out, a high-purity copper (99.99%) was used as a target material. As a result of this study, the material distribution for both magnetron and diode sputtering depositions can be calculated. The feasibility of the ultra-thick coatings growing, devoted to CST production, is demonstrated

Smoothening of the down-skin regions of copper components produced via Laser Powder Bed Fusion technology

Additive manufacturing (AM) is revolutionizing the industrial scenario. Four copper samples have been printed via Laser Powder Bed Fusion (LPBF) at DIAM Laboratory (INFN—Sezione di Padova, Padova, Italy). Samples had different geometrical characteristics, to test the feasibility of the AM as a productive technique for the creation of unsupported copper structures that are characterized by surfaces with a very small inclination angle, where supports cannot be placed. Parts have been printed successfully even in case of 18° of inclination of unsupported walls with respect to the horizontal plane, and on the same samples, surface finishing treatments (performed by Rösler Italiana S.r.l. and INFN-LNL) have been performed to reduce the roughness of the down-facing surfaces. Indeed, the down-skin regions are the most critical areas of AM parts. Several surface treatments are under investigation: mass-finishing treatments (mechanical and chemically assisted mechanical processes), chemical polishing, and electropolishing, and for some of them, the results are extremely positive: from an initial roughness (Ra) of 30–35 µm, the treatments allowed us to achieve a Ra value lower than 1 µm. The study here exposed presents a good way to rapidly reduce the roughness of 3D-printed parts, reaching a mirror-like aspect

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