Studies of RF-Superconductivity Properties of Niobium Film-Coated Cavities at CERN

Benvenuti, C.; Calatroni, S.; Campisi, I.E.; Darriulat, P.; Durand, C.; Peck, Mason A.; Russo, R.

doi:10.1007/978-1-4757-9047-4_8

Cited by 8 publications

(14 citation statements)

References 6 publications

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“…A single relevant study was reported for niobium films on copper [24], which, however, exhibit different microwave behavior from bulk niobium at medium and high fields.…”

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confidence: 99%

“…national Linear Collider an operational gradient is planned to be E acc = 35 MV/m, which corresponds to the peak magnetic field B peak ≈ 150 mT on the cavity surface. Currently, SRF cavities are predominantly made of bulk niobium, and therefore mechanisms contributing to the R s of niobium and its field dependence are under intense investigations[2,[24][25][26][27][28].…”

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confidence: 99%

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Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Romanenko

2013

Applied Physics Letters

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Utilizing difference in temperature dependencies we decoupled BCS and residual components of the microwave surface resistance of superconducting niobium at all rf fields up to B rf ∼ 110 mT.We reveal that the residual resistance decreases with field at B rf < ∼ 40 mT and strongly increases in chemically treated niobium at B rf > 80 mT. We find that BCS surface resistance is weakly dependent on field in the clean limit, whereas a strong and peculiar field dependence emerges after 120 • C vacuum baking.

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“…A single relevant study was reported for niobium films on copper [24], which, however, exhibit different microwave behavior from bulk niobium at medium and high fields.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Romanenko

2013

Applied Physics Letters

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“…These cavities with sputtered niobium layers show a characteristic slope in Q, vs E, . Intensive studies at CERN have been conducted in the last several years to understand this effect and to find sputtering conditions, under which the Q-degradation is absent [37], [43]. The condition of the Cu/Nb interface, its state of oxidation and the migration of impurities at the boundary and within the niobium layer can strongly influence the RF properties; of the deposited films.…”

Section: B Composite Nb/cu Cavitiesmentioning

confidence: 99%

High gradient superconducting niobium cavities. A review of the present status

Kneisel

1999

IEEE Trans. Appl. Supercond.

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Superconducting niobium cavities used in particle accelerators are limited in their rf performance by two phenomena: quench field levels below the theoretical limit of the material caused by defects, and field emission loading resulting from artificial contamination of the superconducting surfaces during surface treatment and assembly procedures. In recent years the community involved in SEW technology developments has successfully improved cavity performances by applying advanced surface treatment methods such as chemical polishing, electropolishing, tumbling, high temperature heat treatment, high pressure rinsing, "in situ" high peak power processing and clean room assembly procedures. In addition, improvements in the material properties such as thermal conductivity by "solid state gettering" and very strict QA methods, both in material inspection and during cavity fabrication, have resulted in cavity performance levels of E,,, up to 40 MV/m in monocells and gradients in the vicinity of 30 MV/m in multicell structures at Q-values of = 10" at a temperature of 2K.More recently the fabrication of "seamless" cavities by spinning is being pursued with encouraging results. This process eliminates electron beam welds, which sometimes are the causes of performance degradations.

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“…Gas content has also been measured on a few niobium films by thermal extraction using eutectic melting, a method already described elsewhere 9 . An UHV vacuum furnace where the released gas is accumulated in a closed volume has been used to melt the samples.…”

Section: Methodsmentioning

confidence: 99%

Study of the discharge gas trapping during thin-film growth

Amorosi¹,

Anderle²,

Benvenuti³

et al. 2001

Vacuum

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Discharge gas trapping in thin films produced by sputtering is known to be due to high energy neutrals bouncing back from the cathode. Qualitatively, the phenomenon is enhanced by raising the discharge voltage and is strongly dependent on the atomic masses of the discharge gas and of the cathode material. In addition to these known effects it is shown that, for a given gas, the trapped amount decreases with increasing the melting temperature of the deposited material. The results obtained both by sample melting and laser ablation are presented and discussed. Paper presented at the 6th European Vacuum Conference University Lyon 1, Campus La Doua/IPNL, Lyon, France 7-10 December 1999 To be published in "Vacuum" Geneva, SwitzerlandDecember 1999* ITC-irst, 38050 Povo TN, Italy -2 - INTRODUCTIONIncorporated sputter gas is often the main impurity found in thin metallic films deposited by sputtering under UHV conditions. Sputtering ions may be neutralised on arriving at the target and be backscattered from it, with an energy which depends mainly on their incident energy and on the target-to-gas atomic mass ratio 1, 2 . This phenomenon results both in mechanical bombardment of the growing film, which influences its crystallographic properties and its adhesion to the substrate, and in gas incorporation. Gas incorporation influences in turn most of the mechanical and electrical characteristics of the film, and controlling its amount allows to fine-tune the film properties, as it has been done for example in the case of superconducting niobium films 3 . Extensive Monte-Carlo calculations are available in literature to estimate the reflection probability and the energy of the reflected atoms for any gas-target combination, as well as the "burial probability" of the gas atoms 4,5 . These data alone are however not sufficient for an easy calculation of the quantity of gas incorporated into a film in a specific coating process. In particular, the precise geometry of the sputtering apparatus, the mean free path of the gas atoms and the nature and the temperature of the substrate on which the film is grown play a determinant role which has to be accounted for separately. Direct measurement of the gas content of films is necessary for estimating these contributions.In this paper, first results of a study of the influence of coating parameters on the gas content of films made with transition metals belonging to the 4a, 5a, 6a columns of the periodic table are presented. The variables explored are the sputtering voltage, the type of sputter gas and its pressure, and the temperature of the films, in planar and in cylindrical magnetron sputtering systems. Preliminary data on the gas contents of films made of ternary alloys of these transition metals are also presented. EXPERIMENTAL PROCEDUREMost of the samples discussed in this paper have been produced using a bakeable, UHV planar magnetron system, with a target 150 mm in diameter and a target-to-substrate distance of 65 mm. The samples, 10 mm x 10 mm in size, have been posit...

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Studies of RF-Superconductivity Properties of Niobium Film-Coated Cavities at CERN

Cited by 8 publications

References 6 publications

Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

Dependence of the microwave surface resistance of superconducting niobium on the magnitude of the rf field

High gradient superconducting niobium cavities. A review of the present status

Study of the discharge gas trapping during thin-film growth

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