Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Sha, Peng; Pan, Weimin; Zhai, Jiyuan; Mi, Zhenghui; Jin, Song; Liu, Baiqi; Dong, Cao; He, Feisi; Ye, Lingxi; He, Xiangcong; Zheng, Shiao

doi:10.3390/app12020546

Cited by 6 publications

(6 citation statements)

References 15 publications

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“…This effect and the lack of a decreasing R BCS is similar to the frequency response of N-doped cavities as EP'ed 650 MHz cavities do not show a decreasing R BCS (Martinello et al, 2021). A similar observation was made in a 650 MHz EP'ed cavity with a 300 °C furnace bake (Sha et al, 2022). Only high rf frequencies above 1 GHz seem to be able to produce this characteristic.…”

Section: Figure 12supporting

confidence: 76%

“…This is similar to the difference between EP'ed and BCP'ed N 2 -doped cavities (Dhakal et al, 2019). Similarly, results on EP'ed 650 MHz ellitpical cavities with either N 2 -doping (Martinello et al, 2021) or a 300 °C bake (Sha et al, 2022) do not show the increasing Q 0 , suggesting that there is a frequency dependence to both treatments.…”

Section: Introductionsupporting

confidence: 74%

“…This simplified process should also increase consistency in larger cavity productions. Since mid-T bakes show a decreasing R BCS with increasing rf field amplitude (Ito et al, 2021;Sha et al, 2022;Steder et al, 2022;Yang et al, 2022), this treatment is of high interest for low frequency SRF cavities that typically operate at a temperature of 4.2 K. At this operating temperature, the surface resistance R s is dominated by its temperature dependent component R BCS and the temperature independent part R Res contributes only a small fraction. A decreasing R BCS at 4 K would be an enormous benefit for SRF based heavy ion accelerators operating in continuous wave (cw) mode at moderate peak surface fields, such as the ISAC-II or FRIB accelerators.…”

Section: Introductionmentioning

confidence: 99%

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Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF

Kolb,

Yao,

Blackburn

et al. 2023

Front. Electron. Mater

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Mid-T heat treatments in the range from 250°C to 400°C on superconducting radio-frequency (SRF) cavities have been shown to provide high quality factors that rise with applied rf field strength in high frequency, electro-polished (EP), elliptical cavities operating at 2 K, similar to nitrogen doped cavities. The rise in quality factor is attributed to a decrease in the temperature dependent part of the surface resistance RBCS. Until now, no results have been reported for these new treatments on quarter-wave resonators (QWR) and half-wave resonators (HWR). The TRIUMF multi-mode coaxial cavities are dedicated test cavities that allow frequency and temperature resolved performance characterization of treatments without changing environments, therefore providing an excellent test vehicle to test these new treatments with rf frequencies ranging from 200 to 1,200 MHz. In this paper, performance measurements from both QWR and HWR cavities are reported and their performance compared with four different treatments: baseline, a conventional 120°C low temperature bake for 48 h, and two mid-T bakes at 300°C and 400°C for 3 h. In addition, sample analysis using SEM, EDX and SIMS of witness samples is also shown. It is found that the mid-T bakes are not directly transferable to low frequency cavities. In the fundamental modes of the two test cavities, no performance gain over the baseline treatment nor a decreasing temperature dependent component with rising rf amplitude was observed. At frequencies above 1 GHz and low temperatures, the mid-T bakes show a reduced field dependence of RBCS compared to both the baseline and 120°C treatments.

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Section: Figure 12supporting

confidence: 76%

Section: Introductionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF

Kolb,

Yao,

Blackburn

et al. 2023

Front. Electron. Mater

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“…celerating cavity [32][33][34]. For superconducting cavities, medium-temperature furnace baking was performed to improve the quality factor [35] and electro-polishing (EP) was conducted to achieve a high gradient [36]. The Casimir force between type-II superconducting plates was calculated [37].…”

Section: Of 23mentioning

confidence: 99%

Magnetic Heating Effect for Quarter-Wave Resonator (QWR) Superconducting Cavities

Kim¹,

Jeon²,

Jung³

et al. 2023

Preprint

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The magnetic heating effect for the superconducting quarter-wave resonator (QWR) cavities is investigated, and the Q slopes of the superconducting cavities are measured with an increasing accelerating field. Physical phenomena for zero-temperature limit are introduced. Bardeen–Cooper–Schrieffer (BCS) resistance and Casimir force are calculated for the zero-temperature limit. The vertical test is shown for the performance test of the quarter-wave resonator (QWR) cavities. The parameters for the quarter-wave resonator (QWR) cavity are presented. The Q slopes are measured as a function of an accelerating electric field at 4.2 K. The surface resistance of the superconducting cavity increases with an increasing peak magnetic field. The magnetic defects cause the degradation for the quality factor. From the magnetic degradation, we can find the magnetic moments of the superconducting cavities. All the quarter-wave resonator (QWR) cryomodules are installed in the tunnel, and beam commissioning is performed successfully.

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“…The mid-T baking was also tested on cavities at higher temperatures and different thermal pre-treatments on large-grain niobium cavities [23], with nitrogen-gas addition [24] and also on 650 MHz cavities [25]. The surface of the Nb samples treated together with cavities was studied primarily by SIMS that allowed determination of the concentration profile in the surface layer characterized mainly by the increase in oxygen-, carbon-and nitrogen-containing species.…”

Section: Introductionmentioning

confidence: 99%

In-situ synchrotron x-ray photoelectron spectroscopy study of medium-temperature baking of niobium for SRF application

Prudnikava,

Tamashevich,

Makarova

et al. 2024

Supercond. Sci. Technol.

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In order to determine optimal parameters of vacuum thermal processing of superconducting radiofrequency niobium cavities exhaustive information on the initial chemical state of niobium and its modification upon a vacuum heat treatment is required. In the present work the chemical composition of the niobium surface upon ultra-high vacuum baking at 200–400 °C similar to “medium-temperature baking” and “furnace baking” of cavities is explored in-situ by synchrotron X-ray photoelectron spectroscopy (XPS). Our findings imply that below the critical thickness of the Nb2O5 layer (≈ 1 nm) niobium starts to interact actively with surface impurities, such as carbon and phosphorus. By studying the kinetics of the native oxide reduction, the activation energy and the rate-constant relation have been determined and used for the calculation of the oxygen-concentration depth profiles. It has been established that the controlled diffusion of oxygen is realized at temperatures 200–300 °C, and the native-oxide layer represents an oxygen source, while at 400 °C the pentoxide is completely reduced and the doping level is determined by an ambient oxygen partial pressure. Fluorine (F to Nb atomic ratio is 0.2) after the buffered chemical polishing was found to be incorporated into the surface layer probed by XPS (≈ 4.6 nm), and its concentration increased during the low-temperature baking (F/Nb=0.35 at 230 °C) and depleted at higher temperatures (F/Nb=0.11 at 400 °C). Thus, the influence of fluorine on the performance of mid-T baked, nitrogen-doped and particularly mild-baked (120 °C/48 h) cavities must be considered. The possible role of fluorine in the educed Nb+5 → Nb+4 reaction under the impact of an X-ray beam at room temperature and during the thermal treatment is also discussed. The range of temperature and duration parameters of the thermal treatment at which the niobium surface would not be contaminated with impurities is determined.

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Quality Factor Enhancement of 650 MHz Superconducting Radio-Frequency Cavity for CEPC

Cited by 6 publications

References 15 publications

Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF

Mid-T heat treatments on BCP’ed coaxial cavities at TRIUMF

Magnetic Heating Effect for Quarter-Wave Resonator (QWR) Superconducting Cavities

In-situ synchrotron x-ray photoelectron spectroscopy study of medium-temperature baking of niobium for SRF application

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