Improvement of Heat-Treated Niobium Surface by In-situ Plasma Treatment Applied to Superconducting RF Resonator

C. Boutelaa; S. Gruszka; C. Cheney; J. Yemane; T. Gerardin; E. Mistretta; J. Demailly; R. Laxdal; P. Kolb; J. Keir; B. Mercier; N. Prud homme; G. Sattonnay; D. Longuevergne

arXiv · 2606.12091

Improvement of Heat-Treated Niobium Surface by In-situ Plasma Treatment Applied to Superconducting RF Resonator

C. Boutelaa·S. Gruszka·C. Cheney·J. Yemane·T. Gerardin·E. Mistretta·J. Demailly·R. Laxdal·P. Kolb·J. Keir·B. Mercier·N. Prud homme·G. Sattonnay·D. Longuevergne

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Abstract

A specific heat treatment at 300 C, named medium-temperature baking (Mid-T baking) is applied to superconducting radio-frequency (SRF) accelerating cavities to improve the quality factor (Qo) at medium accelerating fields (10 to 20 MV/m). This treatment is very successful when done properly as it can reduce by almost a factor of two the power dissipations in this field range. However, surface contamination can lead to the degradation of Qo instead. Plasma-based surface treatment provides an effective approach to eliminate contaminants from the Niobium surface. In this study an insitu plasma cleaning process with argon containing 10 % O2 was performed to remove hydrocarbons from Niobium surface. The treatment was applied before and after a heat treatment at 500 C under ultra-high vacuum conditions (Mid-T baking). Changes in chemical speciation and oxide layer alteration induced by plasma processing were analyzed using insitu X-ray photoelectron spectroscopy (XPS) and exsitu scanning electron microscopy (SEM). The results show that plasma treatment modifies the composition of Niobium oxides, converting a Nb2O5 layer into NbO2. Furthermore, a plasma treatment before Mid-T baking helps reduce unstable oxides such as NbxO and significantly increases the proportion of metallic Niobium at the surface. The Niobium sample treated by plasma prior to Mid-T baking showed a 53 % reduction in carbide formation. Moreover, the C1s component attributed to NbC bonds shifts toward lower binding energy, indicating the formation of a more metallic NbC phase. Whereas without plasma treatment, the higher binding energy component observed after Mid T baking is consistent with Nb2C.

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C. Boutelaa, S. Gruszka, C. Cheney, J. Yemane, T. Gerardin, E. Mistretta, J. Demailly, R. Laxdal, P. Kolb, J. Keir, B. Mercier, N. Prud homme, G. Sattonnay, D. Longuevergne. 2026-06-10. Improvement of Heat-Treated Niobium Surface by In-situ Plasma Treatment Applied to Superconducting RF Resonator. https://arxiv.org/abs/2606.12091

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