Novel SRF Cavity Fabrication
Energy to Power Solutions (e2P) in collaboration with the Thomas Jefferson National Accelerator Facility (JLAB), ExOne Corporation, and the Hackett-Brass Foundry, proposed a revolutionary approach to Nb3Sn SRF cavity fabrication using synergistic technologies consisting of high quality Nb thin films deposited on low cost bulk “casted” bronze (Cu-Sn) substrates. e2P’s proprietary Nb3Sn SRF cavity fabrication process (see US 62/087557 and 62/631,067) can be thought of as the “inverse” process of existing state-of-the-art technology (i.e. Sn diffused bulk Nb) [vi], where the Sn content in our process is provided by an “infinite” reservoir from the underlying bulk bronze (Cu-Sn) scaffold and the higher cost Nb is provided via (thin) film deposition. In this study, multiple samples from five Cu:Sn alloys (89:11, 87:13, 86:14, 85:15, and 81:19) were subjected to the proposed seven step bronze route (BR) Nb3Sn fabrication process (see Table 9), and technical feasibility of each step was clearly demonstrated. In summary, e2P processed twenty 10x10mm square samples for Tc measurements and thirteen 2” round samples for RF measurements. Processing variables investigated included: a) bronze type (Cu:Sn ratio), b) heat treatment temperature (700-800°C), c) heat treament environment vacuum vs. inert Argon, and d) Nb film deposition bias voltage (i.e. ECR ion incident energy). To clarify, a pure Nb film was deposited on each sample via the high ion energy ECR process, NOT a Nb3Sn film. The Nb coated bronze coupons were then heat treated/reacted to allow the Sn from the bronze to diffuse into the Nb via the BR solid state reaction process. All steps of the BR process tested in this study were shown to be technically feasible. The Indirect 3DP fabrication process for the “sand” molds, the bronze casted approach using the 3DP “sand” molds, the surface preparation/polishing of the samples, the ECR Nb film deposition on the samples at various ion incident energies, and both vacuum and argon environment heat treatments at various temperatures all proved effective and successful in this study. Additionally, the majority of the resulting Nb3Sn samples showed promising results with (onset) Tc ~15-18K, sharp transitions widths ΔT< 2 K, and a diamagnetic response ΔL typically larger than the calibration films! Finally, Surface Resistance (Rs) and Quality Factor (Q) measurements were performed on some of the 2” samples. For the three bronze starting ingots with the higher Sn contents, post reacted Nb3Sn samples consistently showed the highest Tc’s and correspondingly highest Sn contents via SEM/EDS. These results are strongly indicative that the heat treat regime for the low Sn contents bronze ingots was insufficient to produce high quality samples with the desired 25% Sn content in the superconducting film from its theoretical phase diagram [16]. This premise if further supported by the following: a 87:13 bronze sample was first heat treated at 700°C for 24hr and Rs measured. Next, the same sample was heat treated at 759°C for an additional 24hr (→48hr total: 24@700°C + 24@759°C) and a 3-4x reduction in Rs was observed after the second heat treatment. In the future, 89:11 and 87:13 Cu:Sn samples will undergo longer heat treatment regimens and/or higher temperatures, or a combination of both. If the resulting Sn concentrations do not show a significant increase trending towards its desired value, the 89:11 and 87:13 samples will be abandoned in Phase II for the higher Sn content bronze, which have demonstrated more consistently superior results. In addition to the Sn content of the bronze alloy and duration of heat treatment, other factors that could affect the Rs and Q results include less than ideal surface preparation and lower quality, ‘R&D’ grade bronze ingots. Additional recommendations include continued base materials and process optimization for Nb3Sn conversion on 2” diameter wafers. While the results from this study are promising, further refinement of the process is necessary to reach full potential.
- Research Organization:
- Tai-Yang Research Compant D/B/A Energy to Power Solutions
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- SC0018713
- OSTI ID:
- 1581006
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-e2P-18713-1
- Country of Publication:
- United States
- Language:
- English
Similar Records
High Critical Current Densities in Nb3Sn Films with Engineered Microstructures--Artifical Pinning Microstructures
Superconducting NbTiN thin films for superconducting radio frequency accelerator cavity applications