Non quadratic RF losses in niobium sputter coated accelerating structures

Durand, C.; Weingarten, W.; Bosland, P.

doi:10.1109/77.402745

Cited by 11 publications

(11 citation statements)

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“…Analyzing data from different cavities [2], the frequency dependence of NQL was compatible with both a linear and a quadratic law. Therefore, we measured it again in the same cavity.…”

Section: A Scope Of Experimentmentioning

confidence: 88%

“…The analytic expression for NQL [2] is (besides numerical factors near unity) equivalent to that of AC losses in a superconductor (Bean model). They are described in linear approximation in B by the surface resistance (with the critical current density j c of Bean's formula [5] replaced by B c2 /(µ 0 l)), .…”

Section: Discussionmentioning

confidence: 99%

“…By equating (1) and (2), and the replacement f(T)→f(T, B) in (2), one obtains for the depth l of the lossy surface layer (3) With a typical conductivity for niobium at room temperature (7.6·10 6 (Ωm) -1 ) and RRR = 10, one obtains a conductivity of σ n = 0.8·10 8 (Ωm) -1 at 10 K. By inserting a crossover frequency close to the observed value, ω c = 2π·3·10 9 s -1 , λ 0 = 85 nm [8], one finds for the depth l = 3 nm. We point out that this number gives only the order of magnitude.…”

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confidence: 99%

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Metallurgical analysis and RF losses in superconducting niobium thin film cavities

Bloess

Durand

Mahner

et al. 1997

IEEE Trans. Appl. Supercond.

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-Copper cavities with a thin niobium film -as used in the large electron positron collider LEP -would be also attractive for future linear colliders, provided the decrease of the Q-value with the accelerating gradient could be reduced. We aim at extracting the important parameters that govern this decrease. The dependence on the RF frequency is studied by exciting 500 MHz and 1500 MHz cavities in different modes. In addition we combined RF measurements for two 1500 MHz cavities of different RF performance with microscopic tests (AFM, TEM) on samples cut out of the same cavities. Their micro-structural characterization in plan-view allows to extract the grain size and the defect densities.

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“…Analyzing data from different cavities [2], the frequency dependence of NQL was compatible with both a linear and a quadratic law. Therefore, we measured it again in the same cavity.…”

Section: A Scope Of Experimentmentioning

confidence: 88%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Metallurgical analysis and RF losses in superconducting niobium thin film cavities

Bloess

Durand

Mahner

et al. 1997

IEEE Trans. Appl. Supercond.

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“…As named by the Durand and Weingarton in their pioneer work, the anomalous RF loss is known as NonQuadratic Loss (NQL), which is caused by the increased external RF field, and contributes in addition to the BCS and residual surface resistance [22]. The different symbols denote different cavities.…”

Section: -1-2 Non-quadratic Rf Lossesmentioning

confidence: 99%

“…When a cavity is carefully prepared, i.e. the NbCu cavity is free from the above two defects (macro defects), it still shows a great Q-value degradation which may be attributed to many loss mechanisms summarized as Non-Quadratic RF losses [22]. A recent experiment showed the copper substrate plays a very important role in resulting cavity performance.…”

Section: -1-1 Current Status Of Nbcu Thin Film Cavitiesmentioning

confidence: 99%

Energetic Deposition of Niobium Thin Film in Vacuum

2001

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(Abstract)Niobium thin films are expected to be free of solid inclusions commonly seen in solid niobium.For particle accelerators, niobium thin film has the potential to replace the solid niobium in the making of the accelerating structures. In order to understand and improve the superconducting performance of niobium thin films at cryogenic temperature, an energetic vacuum deposition system has been developed to study deposition energy effects on the properties of niobium thin films on various substrates. The system directly uses microwave power to create a pure niobium plasma, which can be used to extract niobium ion flux with controllable kinetic energy for direct deposition. The ultra high vacuum avoids the gaseous inclusions in thin films. A retarding field energy analyzer is developed and used to measure the kinetic energy of niobium at the substrate location. A systematic process for thin film characterization is developed and used to analyze the niobium thin films made by this energetic condensation. The properties of niobium thin films at several deposition energies are obtained, and the results show that there exists a preferred deposition energy around 115eV. Acknowledgement iii Acknowledgement Prof. Ron Sundelin has supported me through out the dissertation work at Jefferson Lab. His guidance and help extended beyond the scientific scope, and probably will influence through out my lifetime. Dr. Larry Phillips, as my day-to-day supervisor, looked after many technical details during the system development. Many times, Larry helped to expedite the work requests and material acquisitions. Both Ron and Larry's extensive scientific knowledge made my student life enviable by others. Beside their mentorship, Ron and Larry are also the best friends I can have. They helped me in many ways to settle into the American cultures. Julie Oyer and Chris Thomas helped me in every administrative detail, in a way that I felt "spoiled". I am grateful for their help that I can focus on my dissertation. Fig. 2-3 The illustration of the surface atom nucleation process to show the columnar forming and atom mobility relation………………………………………………………………………………………………………….16 Fig. 2-4 Energetic deposition or condensation is a coating process with the deposition energy well defined in a range above the thermal deposition process and below the ion implantation process. List of TablesThe energy involved in the energetic deposition is variable and depends on the material.Typically, the energy for energetic deposition ranges between 10 and 100 eV. In the energy range well above 200 eV, niobium atoms tend to induce back sputtering resulting in lower deposition rate, thus offering less opportunity to explore energetic deposition. 1-2. Current Implementations in Particle AcceleratorsIt is absolutely not an exaggeration to say that radio frequency superconductivity is the fastest growing technology for particle accelerators. Numerous particle accelerators constructed around the world use or have used accelerating structures based on RF ...

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Superconducting Cavity Resonators

Padamsee

1999

Wiley Encyclopedia of Electrical and Electronics Engineering

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Non quadratic RF losses in niobium sputter coated accelerating structures

Cited by 11 publications

References 24 publications

Metallurgical analysis and RF losses in superconducting niobium thin film cavities

Metallurgical analysis and RF losses in superconducting niobium thin film cavities

Energetic Deposition of Niobium Thin Film in Vacuum

Superconducting Cavity Resonators

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