Comparative studies on enhanced field emission from mechanically and chemically polished broad-area Nb, Cu, and Al cathodes

Pupeter, N.; Habermann, T.; Kirschner, A.; Mahner, E.; Müller, Günter; Piel, H.

doi:10.1016/0169-4332(95)00356-8

Cited by 9 publications

(5 citation statements)

References 12 publications

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“…Copper and other samples coupons can be studied before and after tests, and various types of impurities and defects can be analyzed and monitored. Similar work has been done at the University of Geneva, Switzerland, 14 Cornell University, 15 Wuppertal, Germany, 16 and elsewhere predominantly for superconducting cavities. The suspicion that impurities in crystal boundaries are at least partially responsible for eld emission and rf breakdown has motivated KEK researchers to use HIP hot isostatic pressed metals copper or titanium 17 in a number of their cavities, particularly for their disks.…”

mentioning

confidence: 63%

Field emission and rf breakdown in high-gradient room temperature linac structures

Wang¹,

Loew²

1997

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mentioning

confidence: 63%

Field emission and rf breakdown in high-gradient room temperature linac structures

Wang¹,

Loew²

1997

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“…They showed that the sites were essentially eliminated when the test samples were heated to > 1400° C for 15 minutes. Mahner, Pupeter, and colleagues [32,33] have performed similar studies on copper and niobium. Jimenez and colleagues [34] measured emission sites from metallic, oxide, and sulfide particulate contaminants selectively placed on gold and niobium surfaces.…”

Section: Recent Trends Of Research In the Fieldmentioning

confidence: 78%

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

Stygar¹,

Savage²,

Ives³

et al. 2003

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This research consisted of testing surface treatment processes for stainless steel and aluminum for the purpose of suppressing electron emission over large surface areas to improve the pulsed high voltage hold-off capabilities of these metals. Improvements to hold-off would be beneficial to the operation of the vacuum-insulator grading rings and final self-magnetically insulated transmission line on the ZR-upgrade machine and other pulsed power applications such as flash radiograph and pulsed-microwave machines. The treatments tested for stainless steel include the Z-protocol (chemical polish, HVFF, and gold coating), pulsed E-beam surface treatments by IHCE, Russia, and chromium oxide coatings. Treatments for aluminum were anodized and polymer coatings. Breakdown thresholds also were measured for a range of surface finishes and gap distances. The study found that: 1.) Electrical conditioning and solvent cleaning in a filtered air environment each improve HV hold-off 30%. 2.) Anodized coatings on aluminum give a factor of two improvement in high voltage hold-off. However, anodized aluminum loses this improvement when the damage is severe. Chromium oxide coatings on stainless steel give a 40% and 20% improvement in hold-off before and after damage from many arcs. 3.) Bare aluminum gives similar hold-off for surface roughness, R a , ranging from 0.08 to 3.2 µm. 4.) The various EBEST surfaces tested give high voltage hold-off a factor of two better than typical machined and similar to R a = 0.05 µm polished stainless steel surfaces. 5.) For gaps > 2 mm the hold-off voltage increases as the square root of the gap for bare metal surfaces. This is inconsistent with the accepted model for metals that involves E-field induced electron emission from dielectric inclusions. Micro-particles accelerated across the gap during the voltage pulse give the observed voltage dependence. However the similarity in observed breakdown times for large and small gaps places a requirement that the particles be of molecular size. This makes accelerated micro-particle induced breakdown seem improbable also. 4

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“…46 They designed and built a Field Emission Scanning Microscope, similar to the University of GenevaÕs type, in the same VG ÒEscalabÓ UHV analysis system with the addition of a preparation chamber. 5 Nb with RRR = 1000, 13 as shown in Figure 3.3. This suggestion is evidenced by segregation experiment after mild heating in UHV system.…”

Section: Results From University Of Wuppertalmentioning

confidence: 99%

Enhanced Field Emission Studies on Niobium Surfaces Relevant to High Field Superconducting Radio-Frequency Devices

Wang¹

2002

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Enhanced field emission (EFE) presents the main impediment to higher acceleration gradients in superconducting niobium (Nb) radiofrequency cavities for particle accelerators. The strength, number and sources of EFE sites strongly depend on surface preparation and handling.The main objective of this thesis project is to systematically investigate the sources of EFE from Nb, to evaluate the best available surface preparation techniques with respect to resulting field emission, and to establish an optimized process to minimize or eliminate EFE. To achieve these goals, a scanning field emission microscope (SFEM) was designed and built as an extension to an existing commercial scanning electron microscope (SEM). In the SFEM chamber of ultra high vacuum, a sample is moved laterally in a raster pattern under a high voltage anode tip for EFE detection and localization.The sample is then transferred under vacuum to the SEM chamber equipped with an energy-dispersive x-ray spectrometer for individual emitting site characterization. Compared to other systems built for similar purposes, this apparatus has low cost and maintenance, high operational flexibility, considerably bigger scan area, as well as reliable performance. iv

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Comparative studies on enhanced field emission from mechanically and chemically polished broad-area Nb, Cu, and Al cathodes

Cited by 9 publications

References 12 publications

Field emission and rf breakdown in high-gradient room temperature linac structures

Field emission and rf breakdown in high-gradient room temperature linac structures

Suppression of electron emission from metal electrodes : LDRD 28771 final report.

Enhanced Field Emission Studies on Niobium Surfaces Relevant to High Field Superconducting Radio-Frequency Devices

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