SRF2015 - List of Authors (Navitski, A.)

Paper	Title	Page
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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MOPB072	Characterization of Surface Defects on EXFEL Series and ILC-Higrade Cavities	281
	A. Navitski, E. Elsen, V. Myronenko, J. Schaffran, O. Turkot DESY, Hamburg, Germany Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme. Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed.
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MOPB073	Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities	286
	A. Navitski, E. Elsen, B. Foster DESY, Hamburg, Germany B. Foster, A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, and CRISP (No. 283745). Centrifugal barrel polishing (CBP) is an acid-free surface-polishing technique based on abrasive media. It considerably reduces the usage of chemicals in the preparation of Nb cavities, typically leaving only a final light electropolishing (EP) and achieves considerably smaller roughness than in chemical treatments alone. CBP addresses in particular the removal of pits, welding spatters, deep scratches, and foreign material inclusions that occasionally occur in the production process. A mirror-smooth surface without chemical contamination is also an important enabling step for thin films. Recent results indicate, however, the need of further optimizations, mainly to reduce the surface damaged layer as well as the pollution by the polishing media. A dedicated study of the CBP process using a “coupon” cavity facilitates better polishing characterisation and optimisation by direct measurements of the roughness, removal rate, and removal profile as well as the amount of contamination left behind and determination of a best combination of the CBP and chemical polishing. Results of the coupon-studies and perspectives of the optimizations will be presented and discussed.
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MOPB090	Analysis of Degraded Cavities in Prototype Modules for the European XFEL	355
	S. Aderhold Fermilab, Batavia, Illinois, USA S. Aderhold, D. Kostin, A. Matheisen, A. Navitski, D. Reschke DESY, Hamburg, Germany
	In-between the fabrication and the operation in an accelerator the performance of superconducting RF cavities is typically tested several times. Although the assembly is done under very controlled conditions in a clean room, it is observed from time to time that a cavity with good performance in the vertical acceptance test shows deteriorated performance in the accelerator module afterwards. This work presents the analysis of several such cavities that have been disassembled from modules of the prototype phase for the European XFEL for detailed investigation like additional rf tests, optical inspection and replica.
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MOPB094	Inspection and Repair Techniques for the EXFEL Superconducting 1.3 GHz Cavities at Ettore Zanon S.p.A: Methods and Results	368
	G. Massaro, G. Corniani, N. Maragno Ettore Zanon S.p.A., Schio, Italy A. Matheisen, A. Navitski DESY, Hamburg, Germany P. Michelato, L. Monaco INFN/LASA, Segrate (MI), Italy
	The quality control of the inner surface of superconducting RF cavities is essential in order to assure high accelerating gradient and quality factor. Ettore Zanon S.p.A. (EZ) has implemented in the serial production an optical system that use an high-resolution camera, in order to detect various types of defects. This system is added to a grinding machine, that was specifically designed and built to repair imperfections of the cavities inner surface. This inspection and repair system is applied to recover performance limited cavities of the 1.3 GHz European XFEL project, where surface irregularities are detected, either by the Obacht inspection system at Desy or the optical system at EZ. The optical system and the grinding procedure are qualified using two series cavities limited in gradient and showing different types of surface defects. The performances of these cavities have been recovered to reach the specifications of the project. Until now, all the series XFEL cavities built by EZ, repaired with this technique, have shown an accelerating gradient well above the EXFEL goal.
	Poster MOPB094 [0.795 MB]
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MOPB113	Study of the Evolution of Artificial Defects on the Surface of Niobium During Electrochemical and Chemical Polishing	433
	L. Monaco, P. Michelato INFN/LASA, Segrate (MI), Italy A. Navitski, J. Schaffran, W. Singer DESY, Hamburg, Germany C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy A.L. Prudnikava, Y. Tamashevich University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The presence of defects on the inner surface of Nb superconducting RF structures might limit its final performance. For this reason, strict requirements are imposed during mechanical production of the cavities, specifically on the quality control of the inner surface of components, to avoid the presence of defects or scratches. Nevertheless, some defects may remain also after control or can arise from the following production steps. Understanding the evolution of the defect might shine new insight on its origin and help in defining possible repair techniques. This paper reports the topographical evolution of defects on a Nb sample polished with the standard recipe used for the 1.3 GHz cavities of the EXFEL project. Various artificial defects of different shape, dimensions, and thicknesses/depths, with geometrical characteristics similar to the one that may occur during the machining and handling of cavities, have been “ad hoc” produced on the sample of the same material used for the cell fabrication. Analysis shows the evolution of the shape and profile of the defects at the different polishing steps.
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TUPB079	Second Sound Quench Detection of Dressed TESLA-Shape SRF Cavities	774
	Y. Tamashevich University of Hamburg, Hamburg, Germany E. Elsen, A. Navitski DESY, Hamburg, Germany
	A compact detector and numerical algorithm for second sound measurements has been developed. The detector allows precise 3D quench localisation within a single unit and can be used even for cavities with mounted helium tank. The compact device is easily mounted and requires minimum space. It can be used as a part of the standard cold test of cavities. The results obtained with the new detector and a 3D algorithm have been cross-checked by optical inspection and resistor-based temperature mapping. The resolution of the detector is seen to be limited by the sampling rate and the lateral extent of the quench induced heated area on the Nb superconductor.
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TUPB087	Development of an X-Ray Fluorescence Probe for Inner Cavity Inspection	799
	M. Bertucci, P. Michelato, L. Monaco, M. Moretti, C. Pagani INFN/LASA, Segrate (MI), Italy A. Navitski DESY, Hamburg, Germany
	The development of an x-ray fluorescence probe for detection of foreign material inclusions of the inner surface of 1.3 GHz tesla-type Niobium cavities is here presented. The setup dimensions are minimized so to access the inner cavity volume and focus on the surface of equator. Preliminary tests confirmed the system capability to detect and localize with good precision small metal inclusions of few micrograms. The results obtained from the inspection of some 1.3 GHz XFEL series production cavities are also pointed out.
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Paper

Title

Page

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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MOPB072

Characterization of Surface Defects on EXFEL Series and ILC-Higrade Cavities

281

A. Navitski, E. Elsen, V. Myronenko, J. Schaffran, O. Turkot
DESY, Hamburg, Germany
Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, CRISP (No. 283745) and ”Construction of New Infrastructures-Preparatory Phase” ILC-HiGrade (No. 206711) of the EU 7th FP7/2007-2013 Programme.
Inspection of the inner cavity surface by an optical system is an inexpensive and useful means for surface control and identification of critical or suspicious features. Optical inspection of around 100 EXFEL series and ILC-HiGrade cavities has been performed recently using the high-resolution OBACHT system. It is a semi-automated tool based on the Kyoto camera. To gain information about the 3D topography of surface features or defects, a replica technique has been applied additionally. This is a non-destructive surface-study method reaching resolution down to 1 μm by imprinting the details of the surface onto a hardened rubber. The footprint is subsequently investigated with a microscope or profilometer. Based on these studies, several defects on the surface have been found and classified. Most of the cavity failures leading e.g. to field limitations below 20 MV/m have been identified and corresponding feedback given to the production cycle. Typical surface features and defects as well as their influence on the cavity performance will be presented and discussed.

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

MOPB073

Surface Analyses and Optimization of Centrifugal Barrel Polishing of Nb Cavities

286

A. Navitski, E. Elsen, B. Foster
DESY, Hamburg, Germany
B. Foster, A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

Funding: BMBF project 05H12GU9, Alexander von Humboldt Foundation, and CRISP (No. 283745).
Centrifugal barrel polishing (CBP) is an acid-free surface-polishing technique based on abrasive media. It considerably reduces the usage of chemicals in the preparation of Nb cavities, typically leaving only a final light electropolishing (EP) and achieves considerably smaller roughness than in chemical treatments alone. CBP addresses in particular the removal of pits, welding spatters, deep scratches, and foreign material inclusions that occasionally occur in the production process. A mirror-smooth surface without chemical contamination is also an important enabling step for thin films. Recent results indicate, however, the need of further optimizations, mainly to reduce the surface damaged layer as well as the pollution by the polishing media. A dedicated study of the CBP process using a “coupon” cavity facilitates better polishing characterisation and optimisation by direct measurements of the roughness, removal rate, and removal profile as well as the amount of contamination left behind and determination of a best combination of the CBP and chemical polishing. Results of the coupon-studies and perspectives of the optimizations will be presented and discussed.

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MOPB090

Analysis of Degraded Cavities in Prototype Modules for the European XFEL

355

S. Aderhold
Fermilab, Batavia, Illinois, USA
S. Aderhold, D. Kostin, A. Matheisen, A. Navitski, D. Reschke
DESY, Hamburg, Germany

In-between the fabrication and the operation in an accelerator the performance of superconducting RF cavities is typically tested several times. Although the assembly is done under very controlled conditions in a clean room, it is observed from time to time that a cavity with good performance in the vertical acceptance test shows deteriorated performance in the accelerator module afterwards. This work presents the analysis of several such cavities that have been disassembled from modules of the prototype phase for the European XFEL for detailed investigation like additional rf tests, optical inspection and replica.

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

MOPB094

Inspection and Repair Techniques for the EXFEL Superconducting 1.3 GHz Cavities at Ettore Zanon S.p.A: Methods and Results

368

G. Massaro, G. Corniani, N. Maragno
Ettore Zanon S.p.A., Schio, Italy
A. Matheisen, A. Navitski
DESY, Hamburg, Germany
P. Michelato, L. Monaco
INFN/LASA, Segrate (MI), Italy

The quality control of the inner surface of superconducting RF cavities is essential in order to assure high accelerating gradient and quality factor. Ettore Zanon S.p.A. (EZ) has implemented in the serial production an optical system that use an high-resolution camera, in order to detect various types of defects. This system is added to a grinding machine, that was specifically designed and built to repair imperfections of the cavities inner surface. This inspection and repair system is applied to recover performance limited cavities of the 1.3 GHz European XFEL project, where surface irregularities are detected, either by the Obacht inspection system at Desy or the optical system at EZ. The optical system and the grinding procedure are qualified using two series cavities limited in gradient and showing different types of surface defects. The performances of these cavities have been recovered to reach the specifications of the project. Until now, all the series XFEL cavities built by EZ, repaired with this technique, have shown an accelerating gradient well above the EXFEL goal.

Poster MOPB094 [0.795 MB]

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MOPB113

Study of the Evolution of Artificial Defects on the Surface of Niobium During Electrochemical and Chemical Polishing

433

L. Monaco, P. Michelato
INFN/LASA, Segrate (MI), Italy
A. Navitski, J. Schaffran, W. Singer
DESY, Hamburg, Germany
C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
A.L. Prudnikava, Y. Tamashevich
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

The presence of defects on the inner surface of Nb superconducting RF structures might limit its final performance. For this reason, strict requirements are imposed during mechanical production of the cavities, specifically on the quality control of the inner surface of components, to avoid the presence of defects or scratches. Nevertheless, some defects may remain also after control or can arise from the following production steps. Understanding the evolution of the defect might shine new insight on its origin and help in defining possible repair techniques. This paper reports the topographical evolution of defects on a Nb sample polished with the standard recipe used for the 1.3 GHz cavities of the EXFEL project. Various artificial defects of different shape, dimensions, and thicknesses/depths, with geometrical characteristics similar to the one that may occur during the machining and handling of cavities, have been “ad hoc” produced on the sample of the same material used for the cell fabrication. Analysis shows the evolution of the shape and profile of the defects at the different polishing steps.

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TUPB079

Second Sound Quench Detection of Dressed TESLA-Shape SRF Cavities

774

Y. Tamashevich
University of Hamburg, Hamburg, Germany
E. Elsen, A. Navitski
DESY, Hamburg, Germany

A compact detector and numerical algorithm for second sound measurements has been developed. The detector allows precise 3D quench localisation within a single unit and can be used even for cavities with mounted helium tank. The compact device is easily mounted and requires minimum space. It can be used as a part of the standard cold test of cavities. The results obtained with the new detector and a 3D algorithm have been cross-checked by optical inspection and resistor-based temperature mapping. The resolution of the detector is seen to be limited by the sampling rate and the lateral extent of the quench induced heated area on the Nb superconductor.

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

TUPB087

Development of an X-Ray Fluorescence Probe for Inner Cavity Inspection

799

M. Bertucci, P. Michelato, L. Monaco, M. Moretti, C. Pagani
INFN/LASA, Segrate (MI), Italy
A. Navitski
DESY, Hamburg, Germany

The development of an x-ray fluorescence probe for detection of foreign material inclusions of the inner surface of 1.3 GHz tesla-type Niobium cavities is here presented. The setup dimensions are minimized so to access the inner cavity volume and focus on the surface of equator. Preliminary tests confirmed the system capability to detect and localize with good precision small metal inclusions of few micrograms. The results obtained from the inspection of some 1.3 GHz XFEL series production cavities are also pointed out.

Export •

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