IPAC2016 - List of Authors (Valizadeh, R.)

Paper	Title	Page
WEPMB057	First Results of Magnetic Field Penetration Measurements on Multilayer S-I-S Structures	2245
	O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom A.V. Gurevich ODU, Norfolk, Virginia, USA L. Gurran Lancaster University, Lancaster, United Kingdom L. Gurran Cockcroft Institute, Lancaster University, Lancaster, United Kingdom O.B. Malyshev, S.M. Pattalwar, R. Valizadeh Cockcroft Institute, Warrington, Cheshire, United Kingdom
	The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp=~200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the first results of our measurements of field penetration in Nb thin films and Nb-AlN-Nb multilayer samples at 4.2 K using the magnetic field penetration facility designed, built and tested in ASTeC.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB057
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THPMY016	Graphene Coating for the Reduction of the Secondary Electron Yield	3688
	B.S. Sian, G.X. Xia, G.L. Yu UMAN, Manchester, United Kingdom I. Kinloch, L. Lin, V. Valles University of Manchester, Manchester, United Kingdom O.B. Malyshev, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom O.B. Malyshev, R. Valizadeh, G.X. Xia Cockcroft Institute, Warrington, Cheshire, United Kingdom
	Secondary electron emission is a limiting factor for a performance of many instruments ranging from small gauges and detectors to waveguides and charged particle accelerators. There have been several methods of reducing this effect, e.g. the method of using a material with a low Secondary Electron Yield (SEY) or thin film coating with such a low SEY material. This paper describes the effect of SEY mitigation with graphene coatings on aluminium substrate. The maximum SEY (dmax) was decreased from 2.4 for bare aluminium to 1.4 with a graphene coating. Measurements were taken using an electron gun and a Faraday cup, the electron energies varied between 80 eV and 1 keV with a bias of -18 V on the sample. Other biases of -3, -5, -9, -25, -50 and -75 V were also tested however there was no effect on the SEY.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY016
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TUOCB02	Low Secondary Electron Yield of Laser Treated Surfaces of Copper, Aluminium and Stainless Steel	1089
	R. Valizadeh, P. Goudket, O.B. Malyshev, B.S. Sian, S. Wang STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom M.D. Cropper, S. Wang Loughborough University, Loughborough, Leicestershire, United Kingdom P. Goudket Cockcroft Institute, Warrington, Cheshire, United Kingdom B.S. Sian UMAN, Manchester, United Kingdom N. Sykes Micronanics Laser Solution Center, Didcot, United Kingdom
	Funding: STFC Reduction of SEY was achieved by surface engineering through laser ablation with a laser operating at • = 355 nm. It was shown that the SEY can be reduced to near or below 1 on copper, aluminium and 316LN stainless steel. The laser treated surfaces show an increased surface resistance, with a wide variation in resistance found de-pending on the exact treatment details. However, a treated copper surface with similar surface resistance to aluminium was produced.
	Slides TUOCB02 [94.339 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOCB02
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WEPMB056	CVD Deposition of Nb Based Materials for SRF Cavities	2241
	P. Pizzol, P. Chalker, T. Heil The University of Liverpool, Liverpool, United Kingdom O.B. Malyshev, S.M. Pattalwar, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom G.B.G. Stenning STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom
	Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. Advancements in technology have taken bulk niobium close to its theoretical operational limits, pushing the research to explore novel materials, such as niobium based alloys. Nitrides of niobium offer such an alternative, exhibiting a higher Tc compared to bulk niobium. Replacing then the niobium with a material with better thermal conductivity, such as copper, coated with thin films of nitrides in a multilayer S-I-S would lead to improved performance at reduced cost. Physical vapour deposition (PVD) is currently used to produce these coatings, but it suffers from lack of conformity. This issue can be resolved by using chemical vapour deposition (CVD), which is able to produce high quality coatings over surfaces with a high aspect ratio. This project explores the use of CVD techniques to deposit NbN thin films starting from their chlorinated precursors. The samples obtained are characterized via SEM, FIB, XRD, and EDX.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB056
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WEPMR029	New Material Studies in the Cornell Sample Host Cavity	2338
	J.T. Maniscalco, D.L. Hall, M. Liepe Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA O.B. Malyshev, R. Valizadeh, S. Wilde STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Wilde Loughborough University, Loughborough, Leicestershire, United Kingdom
	Cornell has developed a TE mode sample host microwave cavity in order to study large, flat samples of novel SRF materials. In recent calibration tests, the cavity was shown to reach peak magnetic fields on the sample plate of >100 mT and a quality factor Q₀ greater than 10¹⁰, making it a powerful system to study the performance of superconductors at high RF fields with nOhms sensitivity. In this report we present results of measurements of two samples of thin-film Nb deposited on Cu using HiPIMS at 500 C and at 800 C.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR029
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THPMY017	A Comparison of Surface Properties of Metallic Thin Film Photocathodes	3691
	S. Mistry, M.D. Cropper Loughborough University, Loughborough, Leicestershire, United Kingdom A.N. Hannah, L.B. Jones, K.J. Middleman, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	In this work physical vapour deposition magnetron sputtering has been employed to deposit metallic thin films onto Cu, Mo and Si substrates. The use of metallic thin films offers several advantages: (i) metal photocathodes present a fast response time and a relative insensitivity to the vacuum environment (ii) metallic thin films when prepared and transferred in vacuum can offer smoother and cleaner cathode surfaces. The photocathodes developed here will ultimately be used to drive NCRF guns such as that used in VELA and the proposed CLARA light source test facility. The samples grown on Si substrates were used to investigate the morphology and thickness of the film. The samples grown onto Cu and Mo substrates were analysed and tested as photocathodes in a surface characterisation chamber, where X-Ray photoelectron spectroscopy was employed to determine surface chemistry and a Kelvin probe apparatus used to determine work function. QE measurements were enabled using a 266 nm UV laser.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY017
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Paper

Title

Page

First Results of Magnetic Field Penetration Measurements on Multilayer S-I-S Structures

2245

O.B. Malyshev, K.D. Dumbell, L. Gurran, N. Pattalwar, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
A.V. Gurevich
ODU, Norfolk, Virginia, USA
L. Gurran
Lancaster University, Lancaster, United Kingdom
L. Gurran
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
Cockcroft Institute, Warrington, Cheshire, United Kingdom

The performance of superconducting RF cavities made of bulk Nb is limited by a breakdown field of Bp=~200 mT, close to the superheating field for Nb. A potentially promising solution to enhance the breakdown field of the SRF cavities beyond the intrinsic limits of Nb is a multilayer coating suggested in [1]. In the simplest case, such a multilayer may be a superconductor-insulator-superconductor (S-I-S) coating, for example, bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of another superconductor (S) which could be e.g. dirty niobium [2]. Here we report the first results of our measurements of field penetration in Nb thin films and Nb-AlN-Nb multilayer samples at 4.2 K using the magnetic field penetration facility designed, built and tested in ASTeC.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB057

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

THPMY016

Graphene Coating for the Reduction of the Secondary Electron Yield

3688

B.S. Sian, G.X. Xia, G.L. Yu
UMAN, Manchester, United Kingdom
I. Kinloch, L. Lin, V. Valles
University of Manchester, Manchester, United Kingdom
O.B. Malyshev, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
O.B. Malyshev, R. Valizadeh, G.X. Xia
Cockcroft Institute, Warrington, Cheshire, United Kingdom

Secondary electron emission is a limiting factor for a performance of many instruments ranging from small gauges and detectors to waveguides and charged particle accelerators. There have been several methods of reducing this effect, e.g. the method of using a material with a low Secondary Electron Yield (SEY) or thin film coating with such a low SEY material. This paper describes the effect of SEY mitigation with graphene coatings on aluminium substrate. The maximum SEY (dmax) was decreased from 2.4 for bare aluminium to 1.4 with a graphene coating. Measurements were taken using an electron gun and a Faraday cup, the electron energies varied between 80 eV and 1 keV with a bias of -18 V on the sample. Other biases of -3, -5, -9, -25, -50 and -75 V were also tested however there was no effect on the SEY.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY016

Export •

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

TUOCB02

Low Secondary Electron Yield of Laser Treated Surfaces of Copper, Aluminium and Stainless Steel

1089

R. Valizadeh, P. Goudket, O.B. Malyshev, B.S. Sian, S. Wang
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
M.D. Cropper, S. Wang
Loughborough University, Loughborough, Leicestershire, United Kingdom
P. Goudket
Cockcroft Institute, Warrington, Cheshire, United Kingdom
B.S. Sian
UMAN, Manchester, United Kingdom
N. Sykes
Micronanics Laser Solution Center, Didcot, United Kingdom

Funding: STFC
Reduction of SEY was achieved by surface engineering through laser ablation with a laser operating at • = 355 nm. It was shown that the SEY can be reduced to near or below 1 on copper, aluminium and 316LN stainless steel. The laser treated surfaces show an increased surface resistance, with a wide variation in resistance found de-pending on the exact treatment details. However, a treated copper surface with similar surface resistance to aluminium was produced.

Slides TUOCB02 [94.339 MB]

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-TUOCB02

Export •

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WEPMB056

CVD Deposition of Nb Based Materials for SRF Cavities

2241

P. Pizzol, P. Chalker, T. Heil
The University of Liverpool, Liverpool, United Kingdom
O.B. Malyshev, S.M. Pattalwar, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
G.B.G. Stenning
STFC/RAL/ISIS, Chilton, Didcot, Oxon, United Kingdom

Bulk niobium cavities are widely employed in particle accelerators to create high accelerating gradient despite their high material and operation cost. Advancements in technology have taken bulk niobium close to its theoretical operational limits, pushing the research to explore novel materials, such as niobium based alloys. Nitrides of niobium offer such an alternative, exhibiting a higher Tc compared to bulk niobium. Replacing then the niobium with a material with better thermal conductivity, such as copper, coated with thin films of nitrides in a multilayer S-I-S would lead to improved performance at reduced cost. Physical vapour deposition (PVD) is currently used to produce these coatings, but it suffers from lack of conformity. This issue can be resolved by using chemical vapour deposition (CVD), which is able to produce high quality coatings over surfaces with a high aspect ratio. This project explores the use of CVD techniques to deposit NbN thin films starting from their chlorinated precursors. The samples obtained are characterized via SEM, FIB, XRD, and EDX.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMB056

Export •

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WEPMR029

New Material Studies in the Cornell Sample Host Cavity

2338

J.T. Maniscalco, D.L. Hall, M. Liepe
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
O.B. Malyshev, R. Valizadeh, S. Wilde
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Wilde
Loughborough University, Loughborough, Leicestershire, United Kingdom

Cornell has developed a TE mode sample host microwave cavity in order to study large, flat samples of novel SRF materials. In recent calibration tests, the cavity was shown to reach peak magnetic fields on the sample plate of >100 mT and a quality factor Q₀ greater than 10¹⁰, making it a powerful system to study the performance of superconductors at high RF fields with nOhms sensitivity. In this report we present results of measurements of two samples of thin-film Nb deposited on Cu using HiPIMS at 500 C and at 800 C.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-WEPMR029

Export •

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

THPMY017

A Comparison of Surface Properties of Metallic Thin Film Photocathodes

3691

S. Mistry, M.D. Cropper
Loughborough University, Loughborough, Leicestershire, United Kingdom
A.N. Hannah, L.B. Jones, K.J. Middleman, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

In this work physical vapour deposition magnetron sputtering has been employed to deposit metallic thin films onto Cu, Mo and Si substrates. The use of metallic thin films offers several advantages: (i) metal photocathodes present a fast response time and a relative insensitivity to the vacuum environment (ii) metallic thin films when prepared and transferred in vacuum can offer smoother and cleaner cathode surfaces. The photocathodes developed here will ultimately be used to drive NCRF guns such as that used in VELA and the proposed CLARA light source test facility. The samples grown on Si substrates were used to investigate the morphology and thickness of the film. The samples grown onto Cu and Mo substrates were analysed and tested as photocathodes in a surface characterisation chamber, where X-Ray photoelectron spectroscopy was employed to determine surface chemistry and a Kelvin probe apparatus used to determine work function. QE measurements were enabled using a 266 nm UV laser.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY017

Export •

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