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Ring, Tim

Publications and source records attributed to Ring, Tim.

5 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Towards Field Emission Free Cavity Processing and String Assembly at Fermilab

Cavities and cryomodules assembled at Fermilab have demonstrated unprecedented field emission (FE) free gradients. However, consistent FE-free performance is not guaranteed. Many lessons were learned, and continued vigilance is a must. In addition, several improvements have been identified to further push the state-of-the-art low particulate cavity processing and assembly at Fermilab. Those included the optimization of nitrogen flow, robotic-assisted assembly, and low-particulate fasteners. We share our latest results and vision for the future clean assemblies of cavities and cryomodule strings.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Latest Development of Electropolishing Optimization for 650 MHz Cavity

Electropolishing (EP) of 1.3 GHz niobium (Nb) superconducting RF cavities is conducted to achieve a desired smooth and contaminant-free surface that yields good RF performance. Achieving a smooth surface of a large-sized elliptical cavity with the standard EP conditions was found to be challenging. This work aimed to conduct a systematic parametric EP study to understand the effects of various EP parameters on the surface of 650 MHz cavities used in PIP-II linac. Parameters optimized in this study provided a smooth surface of the cavities. The electropolished cavities met the baseline requirement of field gradient and qualified for further surface treatment to improve the cavity quality factor.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Extra-Cold EP Process at Fermilab

FNAL has established a cold Electro-Polishing (EP) method which maintains the outer surface temperature of cavity cell around 12~15°C during EP process. Cold EP has been applied on the various SRF cavities and contributed to achieve high RF performances with them. To investigate more feasibility and capability of EP at lower temperature, the FNAL EP temperature control tool was recently improved. Extra-cold EP process below 0°C at cavity cell region was successfully performed on 1.3 GHz 1-cell cavity. A compatible RF performance with cold EP method was also demonstrated during the cavity vertical testing. The details of extra-cold EP process and the cavity test results will be presented.

43 PARTICLE ACCELERATORS↗
DOE OSTI2022

Studies on the Fundamental Mechanisms of Niobium Electropolishing

To improve the superconducting performance of niobium SRF cavities, electropolishing (EP) with a sulfuric and hydroflouric acid mixture is used. The chemistry of this reaction is complex due to the interactions between diffusion mechanisms, surface oxide structure, and multiple chemical species. Past studies on the EP process have produced a certain set of optimum parameters that have been used successfully for a long time. However, two recent developments have called the efficacy of the existing EP process into question. Since the introduction of nitrogen doping the surface quality of some cavities has been very poor. Also, EP performed at colder than standard temperatures leads to an increase in the cavity performance. To understand these questions, we perform a multivariate study on the EP process using niobium test samples electropolished at different temperatures and potentials. We find that electropolishing at lower potentials leads to rough surface features such as pitting and grain etching. Some of the surface features show similarities to features seen in niobium cavities. The effect of electropolishing temperature is not clear based on the results of this study.

43 PARTICLE ACCELERATORS↗