IPAC2021 - List of Authors (Wuensch, W.)

Paper	Title	Page
MOPAB344	Machine Learning Models for Breakdown Prediction in RF Cavities for Accelerators	1068
	C. Obermair, A. Apollonio, T. Cartier-Michaud, N. Catalán Lasheras, L. Felsberger, W.L. Millar, W. Wuensch CERN, Geneva, Switzerland C. Obermair, F. Pernkopf TUG, Graz, Austria
	Radio Frequency (RF) breakdowns are one of the most prevalent limits in RF cavities for particle accelerators. During a breakdown, field enhancement associated with small deformations on the cavity surface results in electrical arcs. Such arcs degrade a passing beam and if they occur frequently, they can cause irreparable damage to the RF cavity surface. In this paper, we propose a machine learning approach to predict the occurrence of breakdowns in CERN’s Compact LInear Collider (CLIC) accelerating structures. We discuss state-of-the-art algorithms for data exploration with unsupervised machine learning, breakdown prediction with supervised machine learning, and result validation with Explainable-Artificial Intelligence (Explainable AI). By interpreting the model parameters of various approaches, we go further in addressing opportunities to elucidate the physics of a breakdown and improve accelerator reliability and operation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB344
About •	paper received ※ 20 May 2021 paper accepted ※ 16 July 2021 issue date ※ 11 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB074	S-Band Transverse Deflecting Structure Design for CompactLight	1540
	X.W. Wu, W. Wuensch CERN, Meyrin, Switzerland S. Di Mitri Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy N. Thompson Cockcroft Institute, Warrington, Cheshire, United Kingdom
	The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, which is based on high-gradient X-band (12 GHz) structures. However, to carry out pump-and-probe experiments in the project, two-bunch operation with a spacing of 10 X-band rf cycles is proposed. A sub-harmonic transverse deflecting structure working at S-band is proposed to direct the two bunches into two separate FEL lines. The two FEL pulses will have independently tunable wavelengths and can be combined in a single experiment with a temporal delay between pulses of ± 100 fs. The rf design of the transverse deflector is presented in this paper.
	Poster TUPAB074 [1.557 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB074
About •	paper received ※ 19 May 2021 paper accepted ※ 10 June 2021 issue date ※ 21 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB076	High-Gradient Breakdown Studies of an X-Band Accelerating Structure Operated in the Reversed Taper Direction	1543
	X.W. Wu, N. Catalán Lasheras, A. Grudiev, G. McMonagle, I. Syratchev, W. Wuensch CERN, Meyrin, Switzerland M. Boronat IFIC, Valencia, Spain A. Castilla, A.V. Edwards, W.L. Millar Lancaster University, Lancaster, United Kingdom
	The results of high-gradient tests of a tapered X-band traveling-wave accelerator structure powered in reversed direction are presented. Powering the tapered structure from the small aperture, normally output, at the end of the structure provides unique conditions for the study of gradient limits. This allows high fields in the first cell for a comparatively low input power and a field distribution that rapidly falls off along the length of the structure. A maximum gradient of 130 MV/m in the first cell at a pulse length of 100 ns was reached for an input power of 31.9 MW. Details of the conditioning and operation at high-gradient are presented. Various breakdown rate measurements were conducted at different power levels and rf pulse widths. The structure was standard T24 CLIC test structure and was tested in Xbox-3 at CERN.
	Poster TUPAB076 [1.077 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB076
About •	paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 12 August 2021
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WEPAB374	The Southern Hemisphere’s First X-Band Radio-Frequency Test Facility at the University of Melbourne	3588
	M. Volpi, R.P. Rassool, S.L. Sheehy, G. Taylor, S.D. Williams The University of Melbourne, Melbourne, Victoria, Australia M.J. Boland CLS, Saskatoon, Saskatchewan, Canada M.J. Boland University of Saskatchewan, Saskatoon, Canada N. Catalán Lasheras, S. Gonzalez Anton, G. McMonagle, S. Stapnes, W. Wuensch CERN, Meyrin, Switzerland R.T. Dowd, K. Zingre AS - ANSTO, Clayton, Australia
	The first Southern Hemisphere X-band Laboratory for Accelerators and Beams (X-LAB) is under construction at the University of Melbourne, and it will operate CERN X-band test stand containing two 12GHz 6MW klystron amplifiers. By power combination through hybrid couplers and the use of pulse compressors, up to 50 MW of peak power can be sent to any of 2 test slots at pulse repetition rates up to 400 Hz. The test stand is dedicated to RF conditioning and testing CLIC’s high gradient accelerating structures beyond 100 MV/m. It will also form the basis for developing a compact accelerator for medical applications, such as radiotherapy and compact light sources. Australian researchers working as part of a collaboration between the University of Melbourne, international universities, national industries, the Australian Synchrotron -ANSTO, Canadian Light Source and the CERN believe that creating a laboratory for novel accelerator research in Australia could drive technological and medical innovation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB374
About •	paper received ※ 18 May 2021 paper accepted ※ 06 July 2021 issue date ※ 30 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB380	Measurements of Field Emission Induced Optical Spectra	3602
	R.C. Peacock, G. Burt Lancaster University, Lancaster, United Kingdom S. Calatroni, W. Wuensch CERN, Meyrin, Switzerland
	Field emission induced optical spectra in a dc electrode system have been measured using a spectrometer and CCD camera system in order to gain insight into the nature of field emissions sites. Spectra were measured from between 2 ridged parallel copper electrodes with a gap ranging from 60µm to 100µm and a bias voltage of up to 8000V under high vacuum conditions. A strong correlation between the light intensity of the spectra and the measured field emitted current was observed as a function of applied voltage. A characteristic broadband spectrum ranging from 550nm and 850nm wavelength was observed but there were important features which varied as a function of observation angle, polarity, and conditioning state and also with time. Possible causes of the optical spectra being considered include black body radiation, optical transition radiation and cathode luminescence of copper. Further experiments are ongoing with an improved optical setup to increase optical alignment for measurements with different materials of electrodes, developing further understanding of the cause of the optical spectra, to provide understanding into characteristics and evolution of emission sites.
	Poster WEPAB380 [1.158 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB380
About •	paper received ※ 11 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXB02	Development of 36 GHz RF Systems for RF Linearisers	4518
	A. Castilla, G. Burt Lancaster University, Lancaster, United Kingdom M. Behtouei, B. Spataro INFN/LNF, Frascati, Italy G. Burt Cockcroft Institute, Warrington, Cheshire, United Kingdom J.C. Cai, A. Castilla, A. Latina, X. Liu, I. Syratchev, X.W. Wu, W. Wuensch CERN, Meyrin, Switzerland J.C. Cai, A. Castilla Cockcroft Institute, Lancaster University, Lancaster, United Kingdom A.W. Cross, L. Zhang USTRAT/SUPA, Glasgow, United Kingdom L.J.R. Nix University of Strathclyde, Glasgow, United Kingdom
	Funding: This project has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 777431. As part of the deign studies, the CompactLight project plans to use an injector in the C-band. Which constitutes a particular complication for the harmonic system in charge of linearising the beam’s phase space, since it means its operation frequency could be higher than the standard X-band RF technologies. In the present work, we investigated a 36 GHz (Ka-band) as the ideal frequency for the harmonic system. A set of structure designs are presented as candidates for the lineariser, based on different powering schemes and pulse compressor technologies. The comparison is made both in terms of beam dynamics and RF performance. Given the phase stability requirements for the MW class RF sources needed for this system, we performed careful studies of a Gyro-Klystron and a multi-beam klystron as potential RF sources, with both showing up to 3 MW available power using moderate modulator voltages. Alternatives for pulse compression at Ka-band are also discussed in this work.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-FRXB02
About •	paper received ※ 17 May 2021 paper accepted ※ 19 July 2021 issue date ※ 25 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Machine Learning Models for Breakdown Prediction in RF Cavities for Accelerators

1068

C. Obermair, A. Apollonio, T. Cartier-Michaud, N. Catalán Lasheras, L. Felsberger, W.L. Millar, W. Wuensch
CERN, Geneva, Switzerland
C. Obermair, F. Pernkopf
TUG, Graz, Austria

Radio Frequency (RF) breakdowns are one of the most prevalent limits in RF cavities for particle accelerators. During a breakdown, field enhancement associated with small deformations on the cavity surface results in electrical arcs. Such arcs degrade a passing beam and if they occur frequently, they can cause irreparable damage to the RF cavity surface. In this paper, we propose a machine learning approach to predict the occurrence of breakdowns in CERN’s Compact LInear Collider (CLIC) accelerating structures. We discuss state-of-the-art algorithms for data exploration with unsupervised machine learning, breakdown prediction with supervised machine learning, and result validation with Explainable-Artificial Intelligence (Explainable AI). By interpreting the model parameters of various approaches, we go further in addressing opportunities to elucidate the physics of a breakdown and improve accelerator reliability and operation.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-MOPAB344

About •

paper received ※ 20 May 2021 paper accepted ※ 16 July 2021 issue date ※ 11 August 2021

Export •

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

TUPAB074

S-Band Transverse Deflecting Structure Design for CompactLight

1540

X.W. Wu, W. Wuensch
CERN, Meyrin, Switzerland
S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
N. Thompson
Cockcroft Institute, Warrington, Cheshire, United Kingdom

The CompactLight project is currently developing the design of a next generation hard X-ray FEL facility, which is based on high-gradient X-band (12 GHz) structures. However, to carry out pump-and-probe experiments in the project, two-bunch operation with a spacing of 10 X-band rf cycles is proposed. A sub-harmonic transverse deflecting structure working at S-band is proposed to direct the two bunches into two separate FEL lines. The two FEL pulses will have independently tunable wavelengths and can be combined in a single experiment with a temporal delay between pulses of ± 100 fs. The rf design of the transverse deflector is presented in this paper.

Poster TUPAB074 [1.557 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB074

About •

paper received ※ 19 May 2021 paper accepted ※ 10 June 2021 issue date ※ 21 August 2021

Export •

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

TUPAB076

High-Gradient Breakdown Studies of an X-Band Accelerating Structure Operated in the Reversed Taper Direction

1543

X.W. Wu, N. Catalán Lasheras, A. Grudiev, G. McMonagle, I. Syratchev, W. Wuensch
CERN, Meyrin, Switzerland
M. Boronat
IFIC, Valencia, Spain
A. Castilla, A.V. Edwards, W.L. Millar
Lancaster University, Lancaster, United Kingdom

The results of high-gradient tests of a tapered X-band traveling-wave accelerator structure powered in reversed direction are presented. Powering the tapered structure from the small aperture, normally output, at the end of the structure provides unique conditions for the study of gradient limits. This allows high fields in the first cell for a comparatively low input power and a field distribution that rapidly falls off along the length of the structure. A maximum gradient of 130 MV/m in the first cell at a pulse length of 100 ns was reached for an input power of 31.9 MW. Details of the conditioning and operation at high-gradient are presented. Various breakdown rate measurements were conducted at different power levels and rf pulse widths. The structure was standard T24 CLIC test structure and was tested in Xbox-3 at CERN.

Poster TUPAB076 [1.077 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB076

About •

paper received ※ 19 May 2021 paper accepted ※ 12 July 2021 issue date ※ 12 August 2021

Export •

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

WEPAB374

The Southern Hemisphere’s First X-Band Radio-Frequency Test Facility at the University of Melbourne

3588

M. Volpi, R.P. Rassool, S.L. Sheehy, G. Taylor, S.D. Williams
The University of Melbourne, Melbourne, Victoria, Australia
M.J. Boland
CLS, Saskatoon, Saskatchewan, Canada
M.J. Boland
University of Saskatchewan, Saskatoon, Canada
N. Catalán Lasheras, S. Gonzalez Anton, G. McMonagle, S. Stapnes, W. Wuensch
CERN, Meyrin, Switzerland
R.T. Dowd, K. Zingre
AS - ANSTO, Clayton, Australia

The first Southern Hemisphere X-band Laboratory for Accelerators and Beams (X-LAB) is under construction at the University of Melbourne, and it will operate CERN X-band test stand containing two 12GHz 6MW klystron amplifiers. By power combination through hybrid couplers and the use of pulse compressors, up to 50 MW of peak power can be sent to any of 2 test slots at pulse repetition rates up to 400 Hz. The test stand is dedicated to RF conditioning and testing CLIC’s high gradient accelerating structures beyond 100 MV/m. It will also form the basis for developing a compact accelerator for medical applications, such as radiotherapy and compact light sources. Australian researchers working as part of a collaboration between the University of Melbourne, international universities, national industries, the Australian Synchrotron -ANSTO, Canadian Light Source and the CERN believe that creating a laboratory for novel accelerator research in Australia could drive technological and medical innovation.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB374

About •

paper received ※ 18 May 2021 paper accepted ※ 06 July 2021 issue date ※ 30 August 2021

Export •

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

WEPAB380

Measurements of Field Emission Induced Optical Spectra

3602

R.C. Peacock, G. Burt
Lancaster University, Lancaster, United Kingdom
S. Calatroni, W. Wuensch
CERN, Meyrin, Switzerland

Field emission induced optical spectra in a dc electrode system have been measured using a spectrometer and CCD camera system in order to gain insight into the nature of field emissions sites. Spectra were measured from between 2 ridged parallel copper electrodes with a gap ranging from 60µm to 100µm and a bias voltage of up to 8000V under high vacuum conditions. A strong correlation between the light intensity of the spectra and the measured field emitted current was observed as a function of applied voltage. A characteristic broadband spectrum ranging from 550nm and 850nm wavelength was observed but there were important features which varied as a function of observation angle, polarity, and conditioning state and also with time. Possible causes of the optical spectra being considered include black body radiation, optical transition radiation and cathode luminescence of copper. Further experiments are ongoing with an improved optical setup to increase optical alignment for measurements with different materials of electrodes, developing further understanding of the cause of the optical spectra, to provide understanding into characteristics and evolution of emission sites.

Poster WEPAB380 [1.158 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB380

About •

paper received ※ 11 May 2021 paper accepted ※ 24 June 2021 issue date ※ 24 August 2021

Export •

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

FRXB02

Development of 36 GHz RF Systems for RF Linearisers

4518

A. Castilla, G. Burt
Lancaster University, Lancaster, United Kingdom
M. Behtouei, B. Spataro
INFN/LNF, Frascati, Italy
G. Burt
Cockcroft Institute, Warrington, Cheshire, United Kingdom
J.C. Cai, A. Castilla, A. Latina, X. Liu, I. Syratchev, X.W. Wu, W. Wuensch
CERN, Meyrin, Switzerland
J.C. Cai, A. Castilla
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
A.W. Cross, L. Zhang
USTRAT/SUPA, Glasgow, United Kingdom
L.J.R. Nix
University of Strathclyde, Glasgow, United Kingdom

Funding: This project has received funding from the European Union’s Horizon2020 research and innovation programme under grant agreement No 777431.
As part of the deign studies, the CompactLight project plans to use an injector in the C-band. Which constitutes a particular complication for the harmonic system in charge of linearising the beam’s phase space, since it means its operation frequency could be higher than the standard X-band RF technologies. In the present work, we investigated a 36 GHz (Ka-band) as the ideal frequency for the harmonic system. A set of structure designs are presented as candidates for the lineariser, based on different powering schemes and pulse compressor technologies. The comparison is made both in terms of beam dynamics and RF performance. Given the phase stability requirements for the MW class RF sources needed for this system, we performed careful studies of a Gyro-Klystron and a multi-beam klystron as potential RF sources, with both showing up to 3 MW available power using moderate modulator voltages. Alternatives for pulse compression at Ka-band are also discussed in this work.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-FRXB02

About •

paper received ※ 17 May 2021 paper accepted ※ 19 July 2021 issue date ※ 25 August 2021

Export •

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