IPAC2014 - List of Authors (Lagotzky, S.)

Paper	Title	Page
WEPME004	Prediction of Severe Electron Loading of High-gradient Accelerating Structures based on Field Emission Measurements of Nb and Cu Samples	2258
	S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany
	Funding: The work is funded by BMBF project 05H12PX6. Enhanced field emission (EFE) limits the performance of both superconducting and normal conducting high-gradient accelerating structures. Systematic field emission scanning microscopy and correlated SEM/EDX measurements of relevant Nb and Cu samples have revealed particulates and surface irregularities with field enhancement factors b = 10 - 90 as origin of EFE. Based on sufficient emitter statistics, an exponential increase of the emitter number density N with increasing surface field (E) was found. This allows a prediction of the EFE loading of future ILC and CLIC accelerating structures by scaling of N to relevant E and using a weighted integration over the high-field cavity surface. Accordingly, an electropolished (Ra < 300 nm) and dry-ice cleaned (DIC) TESLA-shape 9-cell 1.3 GHz Nb cavity * will still suffer from EFE at Eacc = 35 MV/m (N = 0.3 /cm² at Epeak = 70 MV/m). Moreover, a diamond-turned, chemically etched and DIC 11.2 GHz Cu structure ** will breakdown at Eacc = 100 MV/m (N = 20 /cm² at Epeak = 243 MV/m). Possible improvements, i.e. by emitter processing will be discussed. * ILC Technical Design Report (2013) ** A. Grudiev and W. Wuensch, Proceedings of LINAC2010, Tsukuba, Japan, pp. 211 - 213
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME004
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WEPME005	Enhanced Field Emission and Emitter Activation on Flat Dry-ice Cleaned Cu Samples	2261
	S. Lagotzky, G. Müller, P. Serbun Bergische Universität Wuppertal, Wuppertal, Germany S. Calatroni, T. Muranaka CERN, Geneva, Switzerland
	Enhanced field emission (EFE), resulting in dark currents and electric breakdowns, is one of the main gradient limitations for the CLIC accelerating structures (actual design Eacc = 100 MV/m, Epeak = 240 MV/m ). Measurements on diamond-turned, flat (Ra = 158 nm) Cu samples showed first EFE at surface fields Es = 130 MV/m. In order to reduce EFE, we have installed a commercial dry ice cleaning (DIC) system in a clean room environment (class iso 5). Accordingly, the number density of emitters (N) was significantly decreased by DIC from N = 52 /cm² to N = 12 /cm² at Es = 190 MV/m. Furthermore we have tested two diamond-turned and chemically etched (SLAC treatment, Ra = 150 nm) Cu samples after DIC resulting in EFE onset at 230 MV/m. Locally measured I(V) curves of the strongest emitters yielded field enhancement factors b = 10 – 90 (10 – 85) on the diamond-turned (chemically etched), respectively. SEM and EDX investigations of the located emission sites revealed surface defects and few particulates (Al, Ca, Si) as origin of the EFE. Moreover, strong emitter activation effects were observed. A possible breakdown mechanism based on this EFE activation will be discussed. A. Grudiev and W. Wuensch, Proceedings of LINAC2010, Tsukuba, Japan, pp. 211 - 213
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME005
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THPRO042	Field Emission Studies of Heat Treated Mo Substrates	2955
	R. Barday, A. Jankowiak, T. Kamps, C. Klimm, J. Knobloch, F. Siewert, A. Varykhalov HZB, Berlin, Germany S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany B. Senkovskiy Technische Universität Dresden, Dresden, Germany
	Funding: This work was supported by German Bundesministerium für Bildung und Forschung project 05K13PX2, Land Berlin and grants of Helmholtz Association. Molybdenum can be used as a substrate for the bi-alkali antimonide photocathodes utilized for the generation of high brightness electron beams in a superconducting radio frequency (SRF) photoinjector cavities. Operation at high field strength is required to obtain a low emittance beam, thus increasing the probability of field emission (FE) from the cathode surface. Usually, substrates are heated in situ before alkali de- position to remove oxide layers from the surface. FE on Mo substrates was measured by means of a field emission scanning microscope (FESM). It turned out that in situ heat treatment (HT) of the Mo surface significantly changes the FE behaviour by activation of new emitters. For a better understanding of the mechanism for enhanced emission after in situ heating a witness Mo sample was investigated using x-ray photoelectron spectroscopy.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO042
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Paper

Title

Page

Prediction of Severe Electron Loading of High-gradient Accelerating Structures based on Field Emission Measurements of Nb and Cu Samples

2258

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

Funding: The work is funded by BMBF project 05H12PX6.
Enhanced field emission (EFE) limits the performance of both superconducting and normal conducting high-gradient accelerating structures. Systematic field emission scanning microscopy and correlated SEM/EDX measurements of relevant Nb and Cu samples have revealed particulates and surface irregularities with field enhancement factors b = 10 - 90 as origin of EFE. Based on sufficient emitter statistics, an exponential increase of the emitter number density N with increasing surface field (E) was found. This allows a prediction of the EFE loading of future ILC and CLIC accelerating structures by scaling of N to relevant E and using a weighted integration over the high-field cavity surface. Accordingly, an electropolished (Ra < 300 nm) and dry-ice cleaned (DIC) TESLA-shape 9-cell 1.3 GHz Nb cavity * will still suffer from EFE at Eacc = 35 MV/m (N = 0.3 /cm² at Epeak = 70 MV/m). Moreover, a diamond-turned, chemically etched and DIC 11.2 GHz Cu structure ** will breakdown at Eacc = 100 MV/m (N = 20 /cm² at Epeak = 243 MV/m). Possible improvements, i.e. by emitter processing will be discussed.
* ILC Technical Design Report (2013)
** A. Grudiev and W. Wuensch, Proceedings of LINAC2010, Tsukuba, Japan, pp. 211 - 213

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME004

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPME005

Enhanced Field Emission and Emitter Activation on Flat Dry-ice Cleaned Cu Samples

2261

S. Lagotzky, G. Müller, P. Serbun
Bergische Universität Wuppertal, Wuppertal, Germany
S. Calatroni, T. Muranaka
CERN, Geneva, Switzerland

Enhanced field emission (EFE), resulting in dark currents and electric breakdowns, is one of the main gradient limitations for the CLIC accelerating structures (actual design Eacc = 100 MV/m, Epeak = 240 MV/m *). Measurements on diamond-turned, flat (Ra = 158 nm) Cu samples showed first EFE at surface fields Es = 130 MV/m. In order to reduce EFE, we have installed a commercial dry ice cleaning (DIC) system in a clean room environment (class iso 5). Accordingly, the number density of emitters (N) was significantly decreased by DIC from N = 52 /cm² to N = 12 /cm² at Es = 190 MV/m. Furthermore we have tested two diamond-turned and chemically etched (SLAC treatment, Ra = 150 nm) Cu samples after DIC resulting in EFE onset at 230 MV/m. Locally measured I(V) curves of the strongest emitters yielded field enhancement factors b = 10 – 90 (10 – 85) on the diamond-turned (chemically etched), respectively. SEM and EDX investigations of the located emission sites revealed surface defects and few particulates (Al, Ca, Si) as origin of the EFE. Moreover, strong emitter activation effects were observed. A possible breakdown mechanism based on this EFE activation will be discussed.
* A. Grudiev and W. Wuensch, Proceedings of LINAC2010, Tsukuba, Japan, pp. 211 - 213

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPME005

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reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPRO042

Field Emission Studies of Heat Treated Mo Substrates

2955

R. Barday, A. Jankowiak, T. Kamps, C. Klimm, J. Knobloch, F. Siewert, A. Varykhalov
HZB, Berlin, Germany
S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany
B. Senkovskiy
Technische Universität Dresden, Dresden, Germany

Funding: This work was supported by German Bundesministerium für Bildung und Forschung project 05K13PX2, Land Berlin and grants of Helmholtz Association.
Molybdenum can be used as a substrate for the bi-alkali antimonide photocathodes utilized for the generation of high brightness electron beams in a superconducting radio frequency (SRF) photoinjector cavities. Operation at high field strength is required to obtain a low emittance beam, thus increasing the probability of field emission (FE) from the cathode surface. Usually, substrates are heated in situ before alkali de- position to remove oxide layers from the surface. FE on Mo substrates was measured by means of a field emission scanning microscope (FESM). It turned out that in situ heat treatment (HT) of the Mo surface significantly changes the FE behaviour by activation of new emitters. For a better understanding of the mechanism for enhanced emission after in situ heating a witness Mo sample was investigated using x-ray photoelectron spectroscopy.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRO042

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)