Pulse Reverse Voltage Electropolishing of Superconducting Radio Frequency Niobium Cavities in Aqueous, Low Concentration Sulfuric Acid Electrolytes without Hydrofluoric Acid
Bibliographic record
Abstract
Niobium superconducting radio frequency cavities (SRF) are required for the International Linear Collider as well as other high energy physics projects. In order for these cavities to achieve the required particle acceleration gradients, electropolishing is conducted as a final surface finishing operation. Conventional electropolishing of SRF cavities is based on the well-established viscous salt film paradigm [[1]] and utilizes a viscous electrolyte consisting of a mixture of sulfuric acid (95-98%) and hydrofluoric acid (49%) in a 9:1 volume ratio [[2]]. The concentrated is included to establish a thick, viscous boundary layer to result in surface brightening or smoothing [[3]]. The hydrofluoric acid is included to remove the niobium oxide film formed during electropolishing [[4]]. Previously we described efforts directed towards demonstrating an innovative electropolishing process for niobium coupons in low concentration (5%) aqueous sulfuric acid without hydrofluoric acid enabled by pulse reverse voltage waveforms electrolyte [[5],[6]]. The advantages of pulse reverse voltage electropolishing are summarized in in Figure 1. Specifically, the forward (anodic) pulse on-time and peak voltage are tuned to eliminate the need for concentrated sulfuric acid; the off-time is adjusted to dissipate heat, and the reverse (cathodic) pulse on-time and peak voltage are tuned to eliminate the need for hydrofluoric acid. In this contribution, we review and describe continuing efforts leading to the scale-up of the electropolishing process to single-cell and three-cell niobium SRF cavities [[7],[8]]. Finally, we present a first order economic comparison of the pulse reverse voltage low concentration aqueous sulfuric acid process compared to baseline concentrated sulfuric acid-hydrofluoric acid process [[9]]. Acknowledgements: The financial support of Faraday corporate, DOE P.O. No. 594128 and DOE Contract No. DE-SC0004588 is acknowledged. [1] Jacquet, P.A. (1936) On the Anodic Behavior of Copper in Aqueous Solutions of Orthophosphoric Acid. Trans. Electrochem. Soc. 69(1) 629-655. [2] Tian, H., Corcoran, S., Reece, C. and Kelly, M. (2008) The Mechanism of Electropolishing of Niobium in Hydrofluoric-Sulfuric Acid Electrolyte. J. Electrochem. Soc., 155, D563-568. [3] D. Landolt,(1987) “Fundamental Aspects of Electropolishing” Electrochimica Acta 32(1) 1-11 (1987). [4] MacDougall, B. (1995) “The Importance of Surface Oxide Films in Corrosion, Semiconductor and Environmental Research” Proceedings of the Symposium on High Rate Metal Dissolution Processes, Vol. 95-19, (Eds. M. Datta, B. MacDougall and J. Fenton) The Electrochemical Society, Pennington, NJ, pp 16-31. [5] M. Inman, E.J. Taylor, T.D. Hall “Electropolishing of Passive Materials in HF-Free Low Viscosity Aqueous Electrolytes” J. Electrochem. Soc., 160(9) E94-E98 (2013). [6] E.J. Taylor, M.E. Inman, T.D. Hall (2015) “Electrochemical system and method for electropolishing superconductive radio frequency cavities” U.S. Patent No. 9,006,147 issued April 14, 2015. [7] E.J. Taylor, T.D. Hall, M. Inman, S. Snyder (2013) “Electropolishing of Niobium SRF Cavities in Low Viscosity Aqueous Electrolytes without Hydroflouric Acid” Paper No. TUP054, Presented SRF2013, Paris, FRANCE. [8] A.M. Rowe, A. Grassellino, T.D. Hall, M.E. Inman, S.T. Snyder, E.J. Taylor (2013) “Bipolar EP: Electropolishing without Flourine in a Water Based Electrolyte” Paper No. TUIOC02, Presented SRF2013, Paris, FRANCE. [9] E.J. Taylor, M. Inman, T. Hall, S. Snyder, A. Rowe, D. Holmes (2015) “Economics of Electropolishing Niobium SRF Cavities in Eco-Friendly Aqueous Electrolytes without Hydrofluoric Acid” Paper No. MOPB092, Presented SRF2015, Whistler, CANADA. Figure 1
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".