SRF2015 - List of Keywords (linear-collider)

Paper	Title	Other Keywords	Page
MOPB058	Field Emission From a Thermally Oxidized Nb Sample	site, vacuum, collider, high-voltage	233
	S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany
	Funding: This work was funded by BMBF project 05H12PX6. Enhanced field emission (EFE) from particulates and surface defects is one of the main field limitations of superconducting Nb cavities required for XFEL and ILC. The activation field Eact of such emitters and the emitter number density N at a given Eact is strongly influenced by the thickness of the Nb oxide layer. Combination of this effect with surface cleaning techniques, e.g. dry ice cleaning (DIC), potentially shifts the onset of EFE to even higher Eact. Therefore, we have started to investigate a single crystal Nb sample after thermal oxidation (TO) by a heat treatment (HT) in air (T = 360°C, t = 40 min). Field emission maps showed a first emitter at 100 MV/m, and N = 30/cm² at 225 MV/m. SEM analysis of the 10 strongest emitters revealed mainly surface defects and one particulate. Subsequent removal of the oxide by a HT (T = 400°C, t = 1 h) under UHV resulted in an EFE onset at 75 MV/m and increased N to 60/cm² at 225 MV/m. In a second step the TO as well as the measurement was repeated after DIC of the surface. The resulting field maps and the SEM analysis of selected emitters will be reported. A.T. Wu et al., MOPC118, IPAC11.
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Paper

Title

Other Keywords

Page

MOPB058

Field Emission From a Thermally Oxidized Nb Sample

site, vacuum, collider, high-voltage

233

S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany

Funding: This work was funded by BMBF project 05H12PX6.
Enhanced field emission (EFE) from particulates and surface defects is one of the main field limitations of superconducting Nb cavities required for XFEL and ILC. The activation field Eact of such emitters and the emitter number density N at a given Eact is strongly influenced by the thickness of the Nb oxide layer*. Combination of this effect with surface cleaning techniques, e.g. dry ice cleaning (DIC), potentially shifts the onset of EFE to even higher Eact. Therefore, we have started to investigate a single crystal Nb sample after thermal oxidation (TO) by a heat treatment (HT) in air (T = 360°C, t = 40 min). Field emission maps showed a first emitter at 100 MV/m, and N = 30/cm² at 225 MV/m. SEM analysis of the 10 strongest emitters revealed mainly surface defects and one particulate. Subsequent removal of the oxide by a HT (T = 400°C, t = 1 h) under UHV resulted in an EFE onset at 75 MV/m and increased N to 60/cm² at 225 MV/m. In a second step the TO as well as the measurement was repeated after DIC of the surface. The resulting field maps and the SEM analysis of selected emitters will be reported.
*A.T. Wu et al., MOPC118, IPAC11.

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