SRF2015 - List of Authors (Lagotzky, S.)

Paper	Title	Page
MOPB058	Field Emission From a Thermally Oxidized Nb Sample	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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MOPB059	Field Emission Investigation of Centrifugal-Barrel-Polished Nb Samples	237
	S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany A. Navitski DESY, Hamburg, Germany A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: This work was funded by BMBF project 05H12PX6. Actual and future SRF-accelerators require high accelerating gradient Eacc and quality factor Q0, which are often limited by enhanced field emission (EFE)* caused by surface roughness or particulates. Various expensive surface preparation techniques (e.g. BCP, EP, HPR etc.) have been developed to obtain the required surface quality and remove the emitters. Recently, centrifugal barrel polishing (CBP) has been reconsidered to obtain a comparable surface roughness as EP with less effort. We have started to investigate Nb samples, which were prepared as coupons in a single cell 1.3 GHz cavity by an optimized five step CBP process with a final dry ice cleaning. EFE maps showed the first emitter (1 nA) at 60 MV/m, and 32 emitters at 110 MV/m. SEM/EDX analysis of the emitting sites revealed many Al2O3 inclusions with sharp edges. Therefore, subsequent BCP (~20 μm removal) was applied to the sample. Surface analysis as well as EFE characterization of CBP treated Nb coupons with/without BCP step will be presented. D. Reschke et al., THPP021, LINAC14. A. Navitski et al., PRSTAB 16, 112001 (2013). *C.A. Cooper, L.D. Cooley, Supercond. Sci. Technol. 26, 015011 (2013).
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Paper

Title

Page

Field Emission From a Thermally Oxidized Nb Sample

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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reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)

MOPB059

Field Emission Investigation of Centrifugal-Barrel-Polished Nb Samples

237

S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany
A. Navitski
DESY, Hamburg, Germany
A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: This work was funded by BMBF project 05H12PX6.
Actual and future SRF-accelerators require high accelerating gradient Eacc and quality factor Q0, which are often limited by enhanced field emission (EFE)* caused by surface roughness or particulates**. Various expensive surface preparation techniques (e.g. BCP, EP, HPR etc.) have been developed to obtain the required surface quality and remove the emitters. Recently, centrifugal barrel polishing (CBP) has been reconsidered to obtain a comparable surface roughness as EP with less effort***. We have started to investigate Nb samples, which were prepared as coupons in a single cell 1.3 GHz cavity by an optimized five step CBP process with a final dry ice cleaning. EFE maps showed the first emitter (1 nA) at 60 MV/m, and 32 emitters at 110 MV/m. SEM/EDX analysis of the emitting sites revealed many Al2O3 inclusions with sharp edges. Therefore, subsequent BCP (~20 μm removal) was applied to the sample. Surface analysis as well as EFE characterization of CBP treated Nb coupons with/without BCP step will be presented.
*D. Reschke et al., THPP021, LINAC14.
**A. Navitski et al., PRSTAB 16, 112001 (2013).
***C.A. Cooper, L.D. Cooley, Supercond. Sci. Technol. 26, 015011 (2013).

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reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text, ※ RIS/RefMan, ※ EndNote (xml)