Dresden 2013 – scientific programme
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HK: Fachverband Physik der Hadronen und Kerne
HK 11: Beschleunigerphysik I (SC, SC-Cavities)
HK 11.5: Talk
Monday, March 4, 2013, 12:15–12:30, WIL-C203
Activation and conditioning of field emitters on flat niobium surfaces — •Stefan Lagotzky and Günter Müller — University of Wuppertal, D-42097 Wuppertal, Germany
Systematic investigations of the enhanced field emission (EFE) from flat (linear roughness < 0.5 µm) and clean polycrystalline niobium (Nb) surfaces revealed an exponential increase of the emitter number density N with the applied electric field and also strong activation effects on particles or surface irregularities. Three possible origins of this emitter activation effect were observed so far: Activation due to high electric fields, due to high temperature, and due to a micro-discharge on the surface [1]. Improved understanding of these processes is important since EFE is one of the main field limitations of superconducting accelerating structures like the XFEL and the ILC. Therefore, we have started a systematic test series with actual large-grain and single crystal Nb samples based on correlated field emission scanning microscopy (FESM) and high-resolution SEM investigations. The EFE properties of these samples were measured before and after controlled in-situ heating at temperatures (times) between 120∘C (24h) and 400∘C (2h). A successive increase of N with the heat treatments (HT) was observed at surface field up to 160 MV/m, i.e. up to 19 emitters/cm2 after HT at 400∘C. Moreover, activated emitters finally showed onset fields down to 40 MV/m. The influence of the HT on the natural oxide layer of Nb and on EFE activation will be discussed.
[1] A. Navitski et. al, submitted to PRSTAB 2013
Ackn. to D. Reschke, J. Ziegler DESY; funded by BMBF 05H12PX6