Experiments on enhanced field emission of niobium cathodes

Mahner, E.; Minatti, N.; Piel, H.; Pupeter, N.

doi:10.1016/0169-4332(93)90289-n

Cited by 34 publications

(12 citation statements)

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“…Niobium was chosen on account of its part in superconducting accelerators RF cavities, where accelerating fields are known to be strongly limited by erratic surface phenomena. [15][16][17][18][19][20][21][22] We wanted the surface shape to be repeatedly ''photographed'' during the continued action of the electric field. Though XRL could be shot with a high repetition rate, Nd-glass pump-laser cooling requires 20 min between successive shots in the present state of art.…”

Section: Experimental Arrangementmentioning

confidence: 99%

Metal-surface mapping by means of soft-x-ray laser interferometry

et al. 1999

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We present an investigation of perturbed surface states performed by using an X-UV laser (ϭ21.2 nm). A dc electric field, which takes increasing values from 0 to 37 MV/m, is continuously applied to the surface of a niobium sample. The surface is irradiated by the pulsed 21.2-nanometer radiation of the X-UV laser, without breaking off the E field. A Fresnel bimirror interferometer supplies surface interferograms, which show the emergence of growing perturbations for an E field about 14 MV/m, even though no electric microbreakdown has yet been recorded between the anode and the Nb sample. The perturbed surface has been observed in a 0.3ϫ9-nm area during hours, before and after an only electric breakdown which occurred at 37 MV/m. Surface maps, obtained by holographic reconstruction from interferograms, show local ''vertical'' surface shifts of 10-19 nm, which are more or less aligned on constant E-field lines. Comparison with ''post-mortem'' surface photographs obtained by the standard scanning electron microscopy method shows perturbation traces only in the small electric breakdown zone, which suggests the extreme-surface structure observed by X-UV laser interferometry to slowly vanish after the end of E-field application.

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Section: Experimental Arrangementmentioning

confidence: 99%

Metal-surface mapping by means of soft-x-ray laser interferometry

et al. 1999

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“…For comparison, one sample (SEP2) about 70 nm step width or by piezo translators with nm resolution. The electrode spacing, d, is controlled by a long distance optical microscope with CCD video camera and varies less than 1 lm for well-tilted flat samples [3]. Emitter distributions were obtained by the voltage scans, V(x, y), with a constant PID-regulated current of 1 nA, the spatial resolution of which is limited by the selected W anode and electrode spacing.…”

Section: Methodsmentioning

confidence: 99%

“…Since electropolished (EP) Nb surfaces are considered to improve the achievable cavity fields, we have started to investigate large area EP Nb samples by means of the dc field emission scanning microscope (FESM) [3]. This apparatus has recently been modernized with new hardware components (Keithley picoamperemeter with 1 kHz rate, FUG power supply with PID regulation) [4] and LabVIEW based programs, resulting in fast voltage scans of large samples thus improving the statistics of the FESM measurements.…”

Section: Introductionmentioning

confidence: 99%

DC field emission scanning measurements on electropolished niobium samples

Dangwal

Reschke

Müller

2006

Physica C: Superconductivity

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“…1 Micron size surface irregularities can seriously affect the performance of high field accelerator cavities 2 by creating field emission ͑FE͒ sites, 3 from where electrons are emitted at much lower electric fields than predicted by Fowler-Nordheim ͑FN͒ theory. 4 This enhanced FE is mainly caused by particulates 5 and surface protrusions 6 due to local field enhancement. Such emitters originate as residues of chemical surface preparation and cleaning techniques, or result from insufficient cleanroom conditions and mishandling of the surface.…”

Section: Introductionmentioning

confidence: 99%

“…19 Therefore, systematic investigations of the dc field emission properties of relevant metallic samples has proven to be helpful for the optimization of surface preparation techniques. In order to understand the origin of the emitters, field emission scanning microscopy ͑FESM͒, 6,20 combined with high-resolution secondary electron microscopy ͑SEM͒ and energy dispersive x-ray analysis ͑EDX͒, is required. 10 Here, we report on the effect of DIC on Cu and Nb surfaces by ͑i͒ comparing the number density of FE sites on particular sample areas scanned in FESM before and after DIC; ͑ii͒ determining the FE properties of localized emitters by current versus voltage ͑I − V͒ measurements and FN analysis; and ͑iii͒ investigating their morphology and composition by SEM and EDX.…”

Section: Introductionmentioning

confidence: 99%

Effective removal of field-emitting sites from metallic surfaces by dry ice cleaning

Dangwal

Müller

Reschke³

et al. 2007

Journal of Applied Physics

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Systematic results of the field emission properties of polycrystalline copper and niobium and single-crystal Nb are reported. Dry ice cleaning ͑DIC͒ is found to suppress enhanced field emission from metallic surfaces. The cleaning effect on the emitting sites was investigated by means of field emission scanning microscopy up to fields of 250 MV/m and high-resolution scanning electron microscopy with energy dispersive x-ray analysis. The number density of emitters at given fields was drastically reduced by dry ice cleaning. Current-voltage measurements and derived Fowler-Nordheim parameters are partially discussed with respect to the morphology and impurity content of localized emitters. No emission from grain boundaries on large-grain Nb samples was observed. The microscopy results prove the effective removal of field-emitting particulates down to 400 nm as well as the partial smoothing of surface protrusions by DIC.

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Experiments on enhanced field emission of niobium cathodes

Cited by 34 publications

References 0 publications

Metal-surface mapping by means of soft-x-ray laser interferometry

Metal-surface mapping by means of soft-x-ray laser interferometry

DC field emission scanning measurements on electropolished niobium samples

Effective removal of field-emitting sites from metallic surfaces by dry ice cleaning

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