IPAC2017 - List of Authors (Barnes, M.J.)

Paper	Title	Page
TUPVA007	Impact of LHC and SPS Injection Kicker Rise Times on Lhc Filling Schemes and Luminosity Reach	2043
	W. Bartmann, M.J. Barnes, J. Boyd, E. Carlier, A. Chmielinska, B. Goddard, G. Kotzian, C. Schwick, L.S. Stoel, D. Valuch, F.M. Velotti, V. Vlachodimitropoulos, C. Wiesner CERN, Geneva, Switzerland
	The 2016 LHC proton filling schemes generally used a spacing between injections of batches of bunches into SPS and LHC corresponding to the design report specification for the SPS and LHC injection kicker rise times, respectively. A reduction of the batch spacing can be directly used to increase luminosity without detrimental effects on beam stability, and with no increase in the number of events per crossing seen by the experiments. Measurements and simulations were performed in SPS and LHC to understand if a shorter injection kicker rise time and associated tighter batch spacing would lead to increased injection oscillations of the first and last bunches of a bunch train and eventually also a systematic growth of the transverse emittance. The results were used to define the minimum possible batch spacing for an acceptable emittance growth in LHC, with gains of reductions of about 10% possible in both machines. The results are discussed, including the potential improvement of the LHC luminosity for different filling schemes.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA007
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WEPVA024	Design of an Inductive Adder for the FCC Injection Kicker Pulse Generator	3312
	D. Woog, M.J. Barnes, L. Ducimetière, J. Holma, T. Kramer CERN, Geneva, Switzerland
	The injection system for a 100 TeV centre-of-mass collider is an important part of the Future Circular Collider (FCC) study. Due to issues with conventional kicker systems, such as self-triggering and long term availability of thyratrons and limitations of HV-cables, innovative design changes are planned for the FCC injection kicker pulse generator. An inductive adder (IA) based on semiconductor (SC) switches is a promising technology for kicker systems. Its modular design, and the possibility of an active ripple suppression are significant advantages. Since the IA is a complex device, with multiple components whose characteristics are important, a detailed design study and construction of a prototype is necessary. This paper summarizes the system requirements and constraints, and describes the main components and design challenges of the prototype IA. It outlines the results from simulations and measurements on different magnetic core materials as well as on SC switches. The paper concludes on the design choices and progress for the prototype to be built at CERN.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA024
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WEPVA094	Study of an Improved Beam Screen Design for the LHC Injection Kicker Magnet for HL-LHC	3471
	V. Vlachodimitropoulos, M.J. Barnes, L. Ducimetière, L. Vega Cid, W.J.M. Weterings CERN, Geneva, Switzerland
	During Run 1 of the LHC, one of the injection kicker magnets (MKIs) occasionally exhibited an excessively high ferrite temperature, caused by coupling of the high intensity beam to the real impedance of the magnet. Beam-screen upgrades have been very effective in reducing beam coupling impedance during Run 2. However, temperature measurements during LHC operation have shown that one end of the MKIs ferrite yoke is consistently hotter than the other: this effect is due to highly non-uniform beam induced power deposition along the kicker. Electromagnetic and thermal simulations show that part of the ferrite yoke will be above its Curie temperature when the LHC is operated with HL-LHC beam parameters, which could increase the turn-around time between fills of the LHC. An impedance mitigation study is presented in this paper with emphasis on the effect of the beam screen layout upon both total beam induced power deposition and its longitudinal distribution. Results of complex thermal simulations, to benchmark the effectiveness of the proposed schemes, are reported. To validate the proposed modification a test bench measurement was performed and preliminary results are discussed
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA094
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WEPVA095	Preliminary Estimate of Beam Induced Power Deposition in a FCC-hh Injection Kicker Magnet	3475
	A. Chmielinska, M.J. Barnes, W. Bartmann, F. Burkart, B. Goddard CERN, Geneva, Switzerland A. Chmielinska EPFL, Lausanne, Switzerland
	The Future Circular Collider for hadrons (FCC-hh) will require a fast injection kicker system that is highly reliable and that does not limit accelerator performance. Important considerations in the design of such a system are machine protection constraints, collider filling factor and hence rise and fall times of the kicker magnet field. Fast rise time kicker magnets are generally ferrite loaded transmission line type magnets with a rectangular shaped aperture. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, beam-induced heating of the ferrite yoke due to the real component of the longitudinal beam coupling impedance needs to be controlled: if the ferrite temperature exceeds the Curie point this impacts the ability to inject beam and hence the availability of the machine. This paper presents estimates for the beam induced power deposition in the ferrite yoke, based on a calculated FCC beam spectrum and an analytical model of longitudinal impedance for unshielded kicker magnets.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA095
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WEPVA096	Thermal Analysis of the LHC Injection Kicker Magnets	3479
	L. Vega Cid, M.J. Barnes, V. Vlachodimitropoulos, W.J.M. Weterings CERN, Geneva, Switzerland A. Abánades ETSII UPM, Madrid, Spain
	Funding: Research supported by the HL-LHC project. The CERN Large Hadron Collider LHC is equipped with two fast pulsed magnet systems (MKIs) that inject particle beams coming from the injector chain. Operation with high intensity beams for many hours can lead to significant beam induced heating of the ferrite yokes of the MKIs. When the ferrite exceeds the Curie temperature of 125°C it loses its magnetic properties, preventing further injection until the ferrite cools down, potentially causing a delay of several hours. Hence important upgrades of the beam-screen were implemented after Run 1 of LHC. However, the High-Luminosity (HL) LHC will be operated with significantly higher intensity beams and hence additional measures are required to limit the ferrite temperature. These magnets operate under ultra-high vacuum conditions: convection is negligible and, as a result of low emissivity of the inside of the vacuum tanks, thermal radiation is limited. A detailed study of the thermal behaviour of these magnets is reported and compared with measurements. In addition several options to improve cooling of the ferrites are presented and analysed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA096
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WEPVA097	Upgrading the SPS Fast Extraction Kicker Systems for HL-LHC	3483
	M.J. Barnes, M.S. Beck, H.A. Day, L. Ducimetière, E. Garcia-Tabares Valdivieso, B. Goddard, H. Neupert, A. Romano, L. Vega Cid, W.J.M. Weterings CERN, Geneva, Switzerland C. Zannini ADAM SA, Geneva, Switzerland
	The CERN SPS has two fast extraction systems, each consisting of travelling wave kicker magnets (MKEs). The beam induced heating in the ferrite yoke of these magnets was historically kept to an acceptable level by implementing water cooling of the kicker magnets: in addition serigraphy was applied on the surfaces of the ferrite yoke facing the beam. Nevertheless, high intensity beams needed in the future for HL-LHC will significantly increase the beam induced heating, potentially raising the MKE ferrite yoke temperature to its Curie point. Hence detailed studies of longitudinal beam coupling impedance were carried out to identify simple but effective methods of further reducing beam induced power deposition. Based on the results of these studies, and in the framework of the LHC Injectors Upgrade (LIU) project, an upgraded MKE kicker magnet was installed during the 2015-2016 shutdown. This paper reports and compares results of predictions, laboratory measurements, temperature measurements during SPS operation, and machine development studies. Measurements of both dynamic pressure rise in the upgraded magnet and Secondary Electron Yield, on samples, are also reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA097
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WEPVA098	Measurements on a 12.5 kV Prototype Inductive Adder for the CLIC DR Extraction Kickers	3487
	J. Holma, M.J. Barnes CERN, Geneva, Switzerland
	The CLIC study is investigating the technical feasibility of an electron-positron collider with high luminosity and a nominal centre-of-mass energy of 3 TeV. The pre-damping rings and damping rings (DRs) will produce ultra-low emittance beam with high bunch charge. To avoid beam emittance increase, the DR kicker systems must provide extremely stable field pulses during injection and extraction of bunches. The DR extraction kicker system consists of a stripline kicker and two pulse modulators. The current specifications for the modulators call for pulses with 160 ns or 900 ns flattop duration of ±12.5 kV and 305 A, with ripple of not more than ±0.02 % (±2.5 V). An inductive adder is a very promising approach to meeting the specifications because analogue modulation methods can be applied to adjust the output waveform. Recently, the first full-scale, 20-layer, 12.5 kV prototype inductive adder has been assembled at CERN and testing has commenced. The goal is to tailor the output waveform of the prototype to the waveform required for the DR extraction stripline kicker. The results of the initial tests and measurements are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA098
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WEPVA099	Influence of Conducting Serigraphy Upon Field Pulse Shape of the SPS Extraction Kicker Systems	3491
	A. Adraktas, M.J. Barnes, L. Ducimetière CERN, Geneva, Switzerland
	Fast pulsed magnets with ferrite yokes are used for beam extraction from the CERN SPS accelerator. These kickers are transmission line type magnets with a rectangular shaped aperture through which the beam circulates. Unless special precautions are taken, the beam impedance of the yoke can provoke significant induced heating, especially for high intensity beams. Previous upgrades of the SPS extraction kicker magnets have included silver fingers serigraphed on the surface of the ferrite facing the beam, to help shield the ferrite yoke from circulating beam. Beam based measurements of the extracted beam indicated that the serigraphy may influence the shape of the field pulse, causing it to increase slightly in magnitude during the flat-top. Hence theoretical studies have been carried out to determine whether the serigraphy influences the field pulse: these studies are reported in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA099
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WEPVA100	Operational Experience of the Upgraded LHC Injection Kicker Magnets During Run 2 and Future Plans	3495
	M.J. Barnes, A. Adraktas, G. Bregliozzi, L. Ducimetière, B. Goddard, B. Salvant, J. Sestak, L. Vega Cid, W.J.M. Weterings, C. Yin Vallgren CERN, Geneva, Switzerland
	During Run 1 of the LHC, one of the injection kicker magnets caused occasional operational delays due to beam induced heating with high bunch intensity and short bunch lengths. In addition, there were also sporadic issues with vacuum activity and electrical flashover of the injection kickers. An extensive program of studies was launched and significant upgrades were carried out during Long Shutdown 1 (LS 1). These upgrades included a new design of beam screen to reduce both beam coupling impedance of the kicker magnet and the electric field associated with the screen conductors, hence decreasing the probability of electrical breakdown in this region. This paper presents operational experience of the injection kicker magnets during the first years of Run 2 of the LHC, including a discussion of faults and kicker magnet issues that limited LHC operation. In addition, in light of these issues, plans for further upgrades are briefly discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA100
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WEPVA101	Review of Stripline Beam Impedance: Application to the Extraction Kicker for the CLIC Damping Rings	3499
	C. Belver-Aguilar, M.J. Barnes CERN, Geneva, Switzerland
	The beam coupling impedance of the stripline kicker for beam extraction from the CLIC Damping Rings (DRs) has been studied analytically, numerically with CST Particle Studio (PS) and measured in the laboratory, although not all the results were understood. In order to have a better knowledge about the beam coupling impedance of a stripline kicker, a simple model has been first studied, with flat electrodes and a cylindrical beam pipe. From this preliminary study, a new approach for the dipolar component of the horizontal impedance has been derived, when considering both odd and even operating modes of the striplines. This new approach has been used to understand the differences found between the predicted transverse impedance and the two wire measurements carried out in the laboratory for the prototype CLIC DR striplines. Future tests of beam coupling impedance with beam in the ALBA Synchrotron Ligth Source will complete this study.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA101
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Paper

Title

Page

Impact of LHC and SPS Injection Kicker Rise Times on Lhc Filling Schemes and Luminosity Reach

2043

W. Bartmann, M.J. Barnes, J. Boyd, E. Carlier, A. Chmielinska, B. Goddard, G. Kotzian, C. Schwick, L.S. Stoel, D. Valuch, F.M. Velotti, V. Vlachodimitropoulos, C. Wiesner
CERN, Geneva, Switzerland

The 2016 LHC proton filling schemes generally used a spacing between injections of batches of bunches into SPS and LHC corresponding to the design report specification for the SPS and LHC injection kicker rise times, respectively. A reduction of the batch spacing can be directly used to increase luminosity without detrimental effects on beam stability, and with no increase in the number of events per crossing seen by the experiments. Measurements and simulations were performed in SPS and LHC to understand if a shorter injection kicker rise time and associated tighter batch spacing would lead to increased injection oscillations of the first and last bunches of a bunch train and eventually also a systematic growth of the transverse emittance. The results were used to define the minimum possible batch spacing for an acceptable emittance growth in LHC, with gains of reductions of about 10% possible in both machines. The results are discussed, including the potential improvement of the LHC luminosity for different filling schemes.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-TUPVA007

Export •

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

WEPVA024

Design of an Inductive Adder for the FCC Injection Kicker Pulse Generator

3312

D. Woog, M.J. Barnes, L. Ducimetière, J. Holma, T. Kramer
CERN, Geneva, Switzerland

The injection system for a 100 TeV centre-of-mass collider is an important part of the Future Circular Collider (FCC) study. Due to issues with conventional kicker systems, such as self-triggering and long term availability of thyratrons and limitations of HV-cables, innovative design changes are planned for the FCC injection kicker pulse generator. An inductive adder (IA) based on semiconductor (SC) switches is a promising technology for kicker systems. Its modular design, and the possibility of an active ripple suppression are significant advantages. Since the IA is a complex device, with multiple components whose characteristics are important, a detailed design study and construction of a prototype is necessary. This paper summarizes the system requirements and constraints, and describes the main components and design challenges of the prototype IA. It outlines the results from simulations and measurements on different magnetic core materials as well as on SC switches. The paper concludes on the design choices and progress for the prototype to be built at CERN.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA024

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WEPVA094

Study of an Improved Beam Screen Design for the LHC Injection Kicker Magnet for HL-LHC

3471

V. Vlachodimitropoulos, M.J. Barnes, L. Ducimetière, L. Vega Cid, W.J.M. Weterings
CERN, Geneva, Switzerland

During Run 1 of the LHC, one of the injection kicker magnets (MKIs) occasionally exhibited an excessively high ferrite temperature, caused by coupling of the high intensity beam to the real impedance of the magnet. Beam-screen upgrades have been very effective in reducing beam coupling impedance during Run 2. However, temperature measurements during LHC operation have shown that one end of the MKIs ferrite yoke is consistently hotter than the other: this effect is due to highly non-uniform beam induced power deposition along the kicker. Electromagnetic and thermal simulations show that part of the ferrite yoke will be above its Curie temperature when the LHC is operated with HL-LHC beam parameters, which could increase the turn-around time between fills of the LHC. An impedance mitigation study is presented in this paper with emphasis on the effect of the beam screen layout upon both total beam induced power deposition and its longitudinal distribution. Results of complex thermal simulations, to benchmark the effectiveness of the proposed schemes, are reported. To validate the proposed modification a test bench measurement was performed and preliminary results are discussed

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA094

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WEPVA095

Preliminary Estimate of Beam Induced Power Deposition in a FCC-hh Injection Kicker Magnet

3475

A. Chmielinska, M.J. Barnes, W. Bartmann, F. Burkart, B. Goddard
CERN, Geneva, Switzerland
A. Chmielinska
EPFL, Lausanne, Switzerland

The Future Circular Collider for hadrons (FCC-hh) will require a fast injection kicker system that is highly reliable and that does not limit accelerator performance. Important considerations in the design of such a system are machine protection constraints, collider filling factor and hence rise and fall times of the kicker magnet field. Fast rise time kicker magnets are generally ferrite loaded transmission line type magnets with a rectangular shaped aperture. The beam coupling impedance of the kicker magnets is crucial, as this can be a dominant contribution to beam instabilities. In addition, beam-induced heating of the ferrite yoke due to the real component of the longitudinal beam coupling impedance needs to be controlled: if the ferrite temperature exceeds the Curie point this impacts the ability to inject beam and hence the availability of the machine. This paper presents estimates for the beam induced power deposition in the ferrite yoke, based on a calculated FCC beam spectrum and an analytical model of longitudinal impedance for unshielded kicker magnets.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA095

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WEPVA096

Thermal Analysis of the LHC Injection Kicker Magnets

3479

L. Vega Cid, M.J. Barnes, V. Vlachodimitropoulos, W.J.M. Weterings
CERN, Geneva, Switzerland
A. Abánades
ETSII UPM, Madrid, Spain

Funding: Research supported by the HL-LHC project.
The CERN Large Hadron Collider LHC is equipped with two fast pulsed magnet systems (MKIs) that inject particle beams coming from the injector chain. Operation with high intensity beams for many hours can lead to significant beam induced heating of the ferrite yokes of the MKIs. When the ferrite exceeds the Curie temperature of 125°C it loses its magnetic properties, preventing further injection until the ferrite cools down, potentially causing a delay of several hours. Hence important upgrades of the beam-screen were implemented after Run 1 of LHC. However, the High-Luminosity (HL) LHC will be operated with significantly higher intensity beams and hence additional measures are required to limit the ferrite temperature. These magnets operate under ultra-high vacuum conditions: convection is negligible and, as a result of low emissivity of the inside of the vacuum tanks, thermal radiation is limited. A detailed study of the thermal behaviour of these magnets is reported and compared with measurements. In addition several options to improve cooling of the ferrites are presented and analysed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA096

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

WEPVA097

Upgrading the SPS Fast Extraction Kicker Systems for HL-LHC

3483

M.J. Barnes, M.S. Beck, H.A. Day, L. Ducimetière, E. Garcia-Tabares Valdivieso, B. Goddard, H. Neupert, A. Romano, L. Vega Cid, W.J.M. Weterings
CERN, Geneva, Switzerland
C. Zannini
ADAM SA, Geneva, Switzerland

The CERN SPS has two fast extraction systems, each consisting of travelling wave kicker magnets (MKEs). The beam induced heating in the ferrite yoke of these magnets was historically kept to an acceptable level by implementing water cooling of the kicker magnets: in addition serigraphy was applied on the surfaces of the ferrite yoke facing the beam. Nevertheless, high intensity beams needed in the future for HL-LHC will significantly increase the beam induced heating, potentially raising the MKE ferrite yoke temperature to its Curie point. Hence detailed studies of longitudinal beam coupling impedance were carried out to identify simple but effective methods of further reducing beam induced power deposition. Based on the results of these studies, and in the framework of the LHC Injectors Upgrade (LIU) project, an upgraded MKE kicker magnet was installed during the 2015-2016 shutdown. This paper reports and compares results of predictions, laboratory measurements, temperature measurements during SPS operation, and machine development studies. Measurements of both dynamic pressure rise in the upgraded magnet and Secondary Electron Yield, on samples, are also reported.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA097

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WEPVA098

Measurements on a 12.5 kV Prototype Inductive Adder for the CLIC DR Extraction Kickers

3487

J. Holma, M.J. Barnes
CERN, Geneva, Switzerland

The CLIC study is investigating the technical feasibility of an electron-positron collider with high luminosity and a nominal centre-of-mass energy of 3 TeV. The pre-damping rings and damping rings (DRs) will produce ultra-low emittance beam with high bunch charge. To avoid beam emittance increase, the DR kicker systems must provide extremely stable field pulses during injection and extraction of bunches. The DR extraction kicker system consists of a stripline kicker and two pulse modulators. The current specifications for the modulators call for pulses with 160 ns or 900 ns flattop duration of ±12.5 kV and 305 A, with ripple of not more than ±0.02 % (±2.5 V). An inductive adder is a very promising approach to meeting the specifications because analogue modulation methods can be applied to adjust the output waveform. Recently, the first full-scale, 20-layer, 12.5 kV prototype inductive adder has been assembled at CERN and testing has commenced. The goal is to tailor the output waveform of the prototype to the waveform required for the DR extraction stripline kicker. The results of the initial tests and measurements are presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA098

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WEPVA099

Influence of Conducting Serigraphy Upon Field Pulse Shape of the SPS Extraction Kicker Systems

3491

A. Adraktas, M.J. Barnes, L. Ducimetière
CERN, Geneva, Switzerland

Fast pulsed magnets with ferrite yokes are used for beam extraction from the CERN SPS accelerator. These kickers are transmission line type magnets with a rectangular shaped aperture through which the beam circulates. Unless special precautions are taken, the beam impedance of the yoke can provoke significant induced heating, especially for high intensity beams. Previous upgrades of the SPS extraction kicker magnets have included silver fingers serigraphed on the surface of the ferrite facing the beam, to help shield the ferrite yoke from circulating beam. Beam based measurements of the extracted beam indicated that the serigraphy may influence the shape of the field pulse, causing it to increase slightly in magnitude during the flat-top. Hence theoretical studies have been carried out to determine whether the serigraphy influences the field pulse: these studies are reported in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA099

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

WEPVA100

Operational Experience of the Upgraded LHC Injection Kicker Magnets During Run 2 and Future Plans

3495

M.J. Barnes, A. Adraktas, G. Bregliozzi, L. Ducimetière, B. Goddard, B. Salvant, J. Sestak, L. Vega Cid, W.J.M. Weterings, C. Yin Vallgren
CERN, Geneva, Switzerland

During Run 1 of the LHC, one of the injection kicker magnets caused occasional operational delays due to beam induced heating with high bunch intensity and short bunch lengths. In addition, there were also sporadic issues with vacuum activity and electrical flashover of the injection kickers. An extensive program of studies was launched and significant upgrades were carried out during Long Shutdown 1 (LS 1). These upgrades included a new design of beam screen to reduce both beam coupling impedance of the kicker magnet and the electric field associated with the screen conductors, hence decreasing the probability of electrical breakdown in this region. This paper presents operational experience of the injection kicker magnets during the first years of Run 2 of the LHC, including a discussion of faults and kicker magnet issues that limited LHC operation. In addition, in light of these issues, plans for further upgrades are briefly discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA100

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WEPVA101

Review of Stripline Beam Impedance: Application to the Extraction Kicker for the CLIC Damping Rings

3499

C. Belver-Aguilar, M.J. Barnes
CERN, Geneva, Switzerland

The beam coupling impedance of the stripline kicker for beam extraction from the CLIC Damping Rings (DRs) has been studied analytically, numerically with CST Particle Studio (PS) and measured in the laboratory, although not all the results were understood. In order to have a better knowledge about the beam coupling impedance of a stripline kicker, a simple model has been first studied, with flat electrodes and a cylindrical beam pipe. From this preliminary study, a new approach for the dipolar component of the horizontal impedance has been derived, when considering both odd and even operating modes of the striplines. This new approach has been used to understand the differences found between the predicted transverse impedance and the two wire measurements carried out in the laboratory for the prototype CLIC DR striplines. Future tests of beam coupling impedance with beam in the ALBA Synchrotron Ligth Source will complete this study.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2017-WEPVA101

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