Conveners
Growth Studies: Session 1
- Stephanie Fernandez (CERN)
Growth Studies: Session 2
- Zeming Sun (CLASSE)
Growth Studies: Session 3
- Tiziana Spina (Fermilab)
Growth Studies: Session 4
- Ryan Porter
A tin vapor diffusion system was constructed for Nb3Sn cavity R&D at KEK. The vapor diffusion system consists of a vertical vacuum furnace, a coating chamber made of niobium, and a heating device for tin evaporation. In the thermal design of the coating system, the temperature distribution of cooling and coating part was investigated using ANSYS. After construction of the vapor diffusion...
There has been significant progress in Nb3Sn SRF cavities during the last decade and the current maximum accelerating electric field of Nb3Sn cavities exceeds ~24 MV/m for a single-cell. Collaborative research on Nb3Sn film growth studies between Fermilab and Northwestern University have been performed during the last three years. We explored effects of growth parameters such as Sn supply...
Improving the performance of Nb3Sn cavities requires altering the growth process to produce better films. A good understanding of how Nb3Sn grows via the Sn diffusion process is required in order to know how to modify the process to achieve a better film. Here we present experimental studies of Nb3Sn layer growth that further our understanding of the Nb3Sn growth process. This includes...
The tin vapor diffusion coating of Nb cavity interiors via a two-step nucleation-then-growth sequence appears to be the most promising path so far to produce Nb3Sn cavities. To elucidate the role of nucleation, we manipulated the accessible range of process variables and studied the niobium surface nucleated under varying process conditions using an array of materials characterization tools....
Nb3Sn is a promising advanced material under development for superconducting radiofrequency (SRF) cavities. Past efforts have been focused primarily on small development-scale cavities, but large, often multi-celled cavities, are needed for particle accelerator applications. In this work, we report on successful Nb3Sn coatings on Nb in a 1 m-long 9-cell Nb sample-host cavity at Fermilab. The...
Following the recent progress made in the Nb₃Sn coatings on single-cell SRF cavities, development is ongoing to reproduce single-cell cavity results on practical SRF structures. Those structures may include multi-cell and single-cell cavities having a larger surface area than regularly coated ~1.5 GHz single-cell cavities. Early CEBAF five-cell cavities coated with a typical coating procedure...
The recently demonstrated performance of Nb3Sn cavities makes this material attractive for SRF accelerator applications. While the majority of research efforts are focused on the development of elliptical single-cell and multi-cell cavities, the potential of this material is evident to other cavity types, which may have complex geometries. We are working towards the development of Nb3Sn-coated...
Helium atom scattering (HAS) and Auger electron spectroscopy (AES) measured surface structure and composition of an unexplored regime of the oxidized Nb surface at SRF Nb3Sn cavity preparation temperatures. These in situ measurements revealed the high temperature stability of a NbO surface reconstruction, specifically the (3x1)-O Nb(100). HAS diffraction peak intensity, line shape, and...
The potential for lowered operating costs and higher quality factors (Q) motivate efforts to implement Nb3Sn based superconducting radio frequency cavities. These benefits are contingent upon the continued optimization of coating procedures resulting in smooth, homogeneous A15 Nb3Sn films. Specifically, the efficiency of Nb3Sn cavity coatings is limited by...
Nb$_{3}$Sn has been identified as a promising next-generation material for superconducting radio frequency (SRF) cavities and there is significant interest in developing protocols resulting in pristine Nb$_{3}$Sn coatings. Recent work has shown that Nb$_{3}$Sn surface structure and composition significantly affects the cavity quality factor (Q) of Nb$_{3}$Sn SRF cavities; Sn homogeneity,...
We report on the PVD deposition of Nb3Sn
on Cu substrates with and without a thick Nb interlayer to
produce Cu/Nb/Nb3Sn and Cu/Nb3Sn multilayer structures.
The Nb3Sn was sputtered directly from an alloy target
at room and elevated temperatures. The dependence of
the superconducting properties of the total structure on
deposition parameters has been determined. The films have
been...
We have investigated Nb3Sn film growth via bronze route by magnetron sputtering of Nb films on to bronze substrates for potential application in SRF cavities. Two main routes were followed: 1) deposition of 500 nm equivalent Nb onto hot (650 °C to 775 °C) bronze substrates, where Nb3Sn formed during the Nb deposition; 2) deposition of Nb onto bronze substrates at lower temperature (200 °C)...
A novel electroplating method to form Nb3Sn film onto an Nb substrate has been developed and optimized at Fermilab. In this method, a Cu interlayer is plated between an Sn layer and the Nb substrate, then a bronze layer formed in the first step of sequential thermal treatment. Subsequently, the Nb3Sn layer is formed at 700C by a solid diffusion reaction between the bronze layer and the Nb...
Electrochemical methods are presented to prepare substrates, deposit Nb and bronze coatings, and set up reactions for Nb3Sn for a potential application in SRF cavities. Specifically, this paper presents firstly our understanding on the electrochemical mechanisms that hinder the proper preparation of substrate and coating layers and secondly methods of overcoming such limitations developed in...
Energy to Power Solutions (e2P) in collaboration with the Thomas Jefferson National Accelerator Facility (JLAB) have investigated a novel approach to fabricating Nb3Sn SRF cavities using an ultra-low cost melt casting fabrication process. e2P's simple melt casting techniques can be used to fabricate nearly any superconducting Nb3Sn structure using either the Bronze Route (BR) or Internal-Tin...
Nb3Sn thin film is the most promising candidate for the next-generation superconducting radio frequency (SRF) cavities. In this work, we successfully enabled the DC sputtering deposition of Nb3Sn films with varying thickness (100 nm - 2 μm) on either Nb or Cu substrates. More importantly, we systematically explored the effects of annealing both in situ and post-sputtering in order to achieve...
Due to higher superconducting critical temperature and superheating field, and lower BCS surface resistance, Nb3Sn is considered a promising alternative to standard niobium for SRF application. Multilayer sequential sputtering method is a promising alternative to the conventional vapor diffusion method to grow Nb3Sn films inside a niobium cavity. In this method, multiple thin layers of Nb and...
In this contribution, we explore the growth of thin superconducting (SC) films, such as Nb3Sn and V3Si, on copper as possible candidates for the reduction of the operational surface resistance of superconducting radio-frequency (SRF) coated cavities for particle accelerators.
For an optimal SRF performance, the SC layers, grown using magnetron sputtering, have to be free of any...
Ultramet, an industry leader in the manufacture of refractory metal and ceramic components by chemical vapor deposition (CVD) and chemical vapor infiltration (CVI), continues to investigate and adapt CVD-based methods for the production of advanced high-gradient capable superconducting radiofrequency (SRF) cavities and components to meet the needs of the accelerator community. Ultramet...
Reducing surface roughness and attaining stoichiometry of Nb3Sn superconductors are required for radio-frequency accelerator applications. We explore the electrochemical deposition of Sn, Nb, and Nb-Sn films, and also investigate the thermal annealing of the plated films to Nb3Sn. Current progress shows that high quality Sn pre-depositions via electroplating on the Nb surface can significantly...
