IPAC2014 - List of Authors (Gai, W.)

Paper	Title	Page
TUPME040	Drive Beam Break-up Control and Practical Gradient Limitation in Collinear Dielectric Wakefield Accelerators	1443
	C. Li, W. Gai, J.G. Power, A. Zholents ANL, Argonne, Ilinois, USA C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA C. Li, C.-X. Tang TUB, Beijing, People's Republic of China
	Dielectric wakefield accelerator (DWA) concept has gained significant attention for the need of the future large scale facilities. For a practical machine, one needs to overcome a major challenge for the DWA that is the efficient energy extraction and stable propagation at the same time for the drive beam. Typically, a slightly off axis beam become unstable in the dielectric channel due to transverse wakefield excitation, that could be controlled if a strong external alternating magnetic focusing channel applied at the same time. However, there is limitation on the practical magnetic field in the focusing channel (typically < 1 Tesla), thus imposing operating point for the DWA. In this article, we explore the operating point of the DWA for various structure frequencies and drive beam charge, particularly on the gradient and total acceleration distance, and provide guidance on the DWA design.
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TUPME058	The Argonne Wakefield Accelerator (AWA): Commissioning and Operation	1503
	M.E. Conde, S.P. Antipov, D.S. Doran, W. Gai, C.-J. Jing, C. Li, W. Liu, J.G. Power, J.Q. Qiu, J.H. Shao, C. Whiteford, E.E. Wisniewski ANL, Argonne, Illinois, USA S.P. Antipov, C.-J. Jing, J.Q. Qiu Euclid TechLabs, LLC, Solon, Ohio, USA S. Cao IMP, Lanzhou, People's Republic of China C. Li, J.H. Shao TUB, Beijing, People's Republic of China E.E. Wisniewski Illinois Institute of Technology, Chicago, Illinois, USA
	Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357. The commissioning of the upgraded AWA facility is well underway. The new L-band electron gun has been fully commissioned and has been successfully operated with its Cesium Telluride photocathode at a gradient of 80 MV/m. Single bunches of up to 100 nC, and bunch trains of four bunches with up to 80 nC per bunch have been generated. The six new accelerating cavities (L-band, seven cells, pi mode) have been RF conditioned to 12 MW or more; their operation at 10 MW brings the beam energy up to 75 MeV. Measurements of the beam parameters are presently underway, and the use of this intense beam to drive high gradient wakefields will soon follow. One of the main goals of the facility is to generate RF pulses with GW power levels, corresponding to accelerating gradients of hundreds of MV/m and energy gains on the order of 100 MeV per structure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME058
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TUPME059	Longitudinal Bunch Shaping with a Double Dogleg based Emittance Exchange Beam Line	1506
	G. Ha, M.E. Conde, W. Gai, C.-J. Jing, K.-J. Kim, J.G. Power, A. Zholents ANL, Argonne, Illinois, USA M.-H. Cho, G. Ha, W. Namkung POSTECH, Pohang, Kyungbuk, Republic of Korea C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA
	Funding: Work supported by High Energy Physics, Office of Science, US DOE. A new program is under development at Argonne National Laboratory (ANL) to use an emittance exchange (EEX) beamline to produce longitudinally shaped electron bunches. While the ultimate goal is to generate triangular shapes for high transformer ratio wakefield acceleration we are also exploring, in general, the capability of the double dogleg EEX beamline to control the bunch shape. We are studying effects that degrade the quality of the longitudinal current profile including: non-uniform particle distribution, emittance, the deflecting cavity thick-lens effect, 2nd order effects, space charge effects and coherent synchrotron radiation effects. We will present the double dogleg EEX beamline layout and the diagnostic design as well as give a progress report on the experimental status of the program.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME059
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WEPRO118	THz Radiation Generation in Multimode Wakefield Structures	2248
	S.P. Antipov, S.V. Baryshev, C.-J. Jing, A. Kanareykin, P. Schoessow Euclid TechLabs, LLC, Solon, Ohio, USA M.G. Fedurin BNL, Upton, Long Island, New York, USA W. Gai, A. Zholents ANL, Argonne, Ilinois, USA D. Wang TUB, Beijing, People's Republic of China
	Funding: DOE SBIR A number of methods for producing sub-picosecond electron bunches have been demonstrated in recent years. A train of these bunches is capable of generating THz radiation via multiple mechanisms like transition, Cherenkov and undulator radiation. We propose to use a bunch train like this to selectively excite a high order mode in a dielectric wakefield structure. This allows us to use wakefield structures that are geometrically larger and easier to fabricate for beam-based THz generation. In this paper we present a THz source design based on this concept and experimental progress to date.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRO118
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THOAB03	A High Resolution Spatial-temporal Imaging Diagnostic for High Energy Density Physics Experiments	2819
	W. Gai ANL, Argonne, Illinois, USA S. Cao, H.S. Xu, W.-L. Zhan, Z.M. Zhang, Y.T. Zhao IMP, Lanzhou, People's Republic of China J.Q. Qiu Euclid TechLabs, LLC, Solon, Ohio, USA C.-X. Tang TUB, Beijing, People's Republic of China
	We present a scheme that uses a high energy electron beam as a probe for time resolved (~ pico – nano seconds) imaging measurements of high energy density processes in materials with spatial resolution of < 1 μm. The device uses an electron bunch train with a flexible time structure penetrating a time varying high density target. By imaging the scattered electron beam, the detailed target profile and its density evolution can be accurately determined. In this paper, we discuss the viability of the concept and show that for densities in the range up to 400 gram/cm³, an electron beam consisting of a train of ~800 MeV bunchlets, each a few ps long and with charges ~nC is suitable. Successful demonstration of this concept will have a major impact for both future fusion science and HEDP physics research.
	Slides THOAB03 [2.493 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THOAB03
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THPRI059	Field Emission Study of RF cavity in Static Magnetic Field	3905
	T.H. Luo, D. Li LBNL, Berkeley, California, USA W. Gai ANL, Argonne, Illinois, USA J.H. Shao TUB, Beijing, People's Republic of China
	The RF cavity performance in solenoid magnetic field is crucial for the muon ionization cooling. Previous experiments have shown that the strong external magnetic field can significantly lower the maximum achievable RF voltage in the cavity. The mechanism of this performance degradation has been studied both analytically and experimentally, but so far no conclusive cause has been determined yet. In this paper, we propose an experiment to study the effect of a static B field on the field emission in the RF cavity, which hasn't been investigated before, and which can contribute to the cavity performance degradation in the solenoid field.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI059
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THPRI060	Conceptual Design of an Electromagnetic Driven Undulator Based Positron Target System for ILC	3908
	W. Gai, W. Liu ANL, Argonne, Illinois, USA
	There have been intense activities on development of the fast spinning Ti wheel positron target for ILC in the last few years. As in many high power target design, it requires solutions for many technical challenges, such as vacuum, thermal stress and radiation damage control, just to name a few. Due to the unique beam timing structure, in this paper, we present a target system based on a electromagnetic mechanical system that drives a bullet type Ti slug (~ 1.4x1.4x10 cm, weigh ~ 50 g) as the target system. The mechanism is similar to a reloadable EM rail gun driven projectiles. The system can be compact, vacuum isolated, and ease of cooling. Conceptual design layout and parameter estimations are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI060
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THPRI076	Laser Triggered RF Breakdown Study Using an S-band Photocathode Gun	3943
	J.H. Shao, W. Gai ANL, Argonne, Illinois, USA H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, C.-X. Tang, L.X. Yan TUB, Beijing, People's Republic of China C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA F.Y. Wang SLAC, Menlo Park, California, USA
	A laser triggered RF breakdown experiment was carried out with an S-band photocathode gun at Tsinghua University for attempting understanding of the RF breakdown processes. By systematic measurement of the time dependence of the breakdown current at the gun exit and the stored RF energy in the cavity, one might gain insight into the time evolution of RF breakdown physics. A correlation of the stored energy and field emission current has been analysed with an equivalent circuit model. Experimental details and analysis methods are reported.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI076
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THPRI077	Electric Field Enhancement Study using an L-band Photocathode Gun	3946
	J.H. Shao, W. Gai ANL, Argonne, Illinois, USA H.B. Chen, J. Shi TUB, Beijing, People's Republic of China C.-J. Jing Euclid TechLabs, LLC, Solon, Ohio, USA F.Y. Wang, L. Xiao SLAC, Menlo Park, California, USA
	RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI077
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Paper

Title

Page

Drive Beam Break-up Control and Practical Gradient Limitation in Collinear Dielectric Wakefield Accelerators

1443

C. Li, W. Gai, J.G. Power, A. Zholents
ANL, Argonne, Ilinois, USA
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
C. Li, C.-X. Tang
TUB, Beijing, People's Republic of China

Dielectric wakefield accelerator (DWA) concept has gained significant attention for the need of the future large scale facilities. For a practical machine, one needs to overcome a major challenge for the DWA that is the efficient energy extraction and stable propagation at the same time for the drive beam. Typically, a slightly off axis beam become unstable in the dielectric channel due to transverse wakefield excitation, that could be controlled if a strong external alternating magnetic focusing channel applied at the same time. However, there is limitation on the practical magnetic field in the focusing channel (typically < 1 Tesla), thus imposing operating point for the DWA. In this article, we explore the operating point of the DWA for various structure frequencies and drive beam charge, particularly on the gradient and total acceleration distance, and provide guidance on the DWA design.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME040

Export •

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

TUPME058

The Argonne Wakefield Accelerator (AWA): Commissioning and Operation

1503

M.E. Conde, S.P. Antipov, D.S. Doran, W. Gai, C.-J. Jing, C. Li, W. Liu, J.G. Power, J.Q. Qiu, J.H. Shao, C. Whiteford, E.E. Wisniewski
ANL, Argonne, Illinois, USA
S.P. Antipov, C.-J. Jing, J.Q. Qiu
Euclid TechLabs, LLC, Solon, Ohio, USA
S. Cao
IMP, Lanzhou, People's Republic of China
C. Li, J.H. Shao
TUB, Beijing, People's Republic of China
E.E. Wisniewski
Illinois Institute of Technology, Chicago, Illinois, USA

Funding: Work supported by the U.S. Department of Energy under contract No. DE-AC02-06CH11357.
The commissioning of the upgraded AWA facility is well underway. The new L-band electron gun has been fully commissioned and has been successfully operated with its Cesium Telluride photocathode at a gradient of 80 MV/m. Single bunches of up to 100 nC, and bunch trains of four bunches with up to 80 nC per bunch have been generated. The six new accelerating cavities (L-band, seven cells, pi mode) have been RF conditioned to 12 MW or more; their operation at 10 MW brings the beam energy up to 75 MeV. Measurements of the beam parameters are presently underway, and the use of this intense beam to drive high gradient wakefields will soon follow. One of the main goals of the facility is to generate RF pulses with GW power levels, corresponding to accelerating gradients of hundreds of MV/m and energy gains on the order of 100 MeV per structure.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME058

Export •

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TUPME059

Longitudinal Bunch Shaping with a Double Dogleg based Emittance Exchange Beam Line

1506

G. Ha, M.E. Conde, W. Gai, C.-J. Jing, K.-J. Kim, J.G. Power, A. Zholents
ANL, Argonne, Illinois, USA
M.-H. Cho, G. Ha, W. Namkung
POSTECH, Pohang, Kyungbuk, Republic of Korea
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA

Funding: Work supported by High Energy Physics, Office of Science, US DOE.
A new program is under development at Argonne National Laboratory (ANL) to use an emittance exchange (EEX) beamline to produce longitudinally shaped electron bunches. While the ultimate goal is to generate triangular shapes for high transformer ratio wakefield acceleration we are also exploring, in general, the capability of the double dogleg EEX beamline to control the bunch shape. We are studying effects that degrade the quality of the longitudinal current profile including: non-uniform particle distribution, emittance, the deflecting cavity thick-lens effect, 2nd order effects, space charge effects and coherent synchrotron radiation effects. We will present the double dogleg EEX beamline layout and the diagnostic design as well as give a progress report on the experimental status of the program.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-TUPME059

Export •

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WEPRO118

THz Radiation Generation in Multimode Wakefield Structures

2248

S.P. Antipov, S.V. Baryshev, C.-J. Jing, A. Kanareykin, P. Schoessow
Euclid TechLabs, LLC, Solon, Ohio, USA
M.G. Fedurin
BNL, Upton, Long Island, New York, USA
W. Gai, A. Zholents
ANL, Argonne, Ilinois, USA
D. Wang
TUB, Beijing, People's Republic of China

Funding: DOE SBIR
A number of methods for producing sub-picosecond electron bunches have been demonstrated in recent years. A train of these bunches is capable of generating THz radiation via multiple mechanisms like transition, Cherenkov and undulator radiation. We propose to use a bunch train like this to selectively excite a high order mode in a dielectric wakefield structure. This allows us to use wakefield structures that are geometrically larger and easier to fabricate for beam-based THz generation. In this paper we present a THz source design based on this concept and experimental progress to date.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-WEPRO118

Export •

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

THOAB03

A High Resolution Spatial-temporal Imaging Diagnostic for High Energy Density Physics Experiments

2819

W. Gai
ANL, Argonne, Illinois, USA
S. Cao, H.S. Xu, W.-L. Zhan, Z.M. Zhang, Y.T. Zhao
IMP, Lanzhou, People's Republic of China
J.Q. Qiu
Euclid TechLabs, LLC, Solon, Ohio, USA
C.-X. Tang
TUB, Beijing, People's Republic of China

We present a scheme that uses a high energy electron beam as a probe for time resolved (~ pico – nano seconds) imaging measurements of high energy density processes in materials with spatial resolution of < 1 μm. The device uses an electron bunch train with a flexible time structure penetrating a time varying high density target. By imaging the scattered electron beam, the detailed target profile and its density evolution can be accurately determined. In this paper, we discuss the viability of the concept and show that for densities in the range up to 400 gram/cm³, an electron beam consisting of a train of ~800 MeV bunchlets, each a few ps long and with charges ~nC is suitable. Successful demonstration of this concept will have a major impact for both future fusion science and HEDP physics research.

Slides THOAB03 [2.493 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THOAB03

Export •

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THPRI059

Field Emission Study of RF cavity in Static Magnetic Field

3905

T.H. Luo, D. Li
LBNL, Berkeley, California, USA
W. Gai
ANL, Argonne, Illinois, USA
J.H. Shao
TUB, Beijing, People's Republic of China

The RF cavity performance in solenoid magnetic field is crucial for the muon ionization cooling. Previous experiments have shown that the strong external magnetic field can significantly lower the maximum achievable RF voltage in the cavity. The mechanism of this performance degradation has been studied both analytically and experimentally, but so far no conclusive cause has been determined yet. In this paper, we propose an experiment to study the effect of a static B field on the field emission in the RF cavity, which hasn't been investigated before, and which can contribute to the cavity performance degradation in the solenoid field.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI059

Export •

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

THPRI060

Conceptual Design of an Electromagnetic Driven Undulator Based Positron Target System for ILC

3908

W. Gai, W. Liu
ANL, Argonne, Illinois, USA

There have been intense activities on development of the fast spinning Ti wheel positron target for ILC in the last few years. As in many high power target design, it requires solutions for many technical challenges, such as vacuum, thermal stress and radiation damage control, just to name a few. Due to the unique beam timing structure, in this paper, we present a target system based on a electromagnetic mechanical system that drives a bullet type Ti slug (~ 1.4x1.4x10 cm, weigh ~ 50 g) as the target system. The mechanism is similar to a reloadable EM rail gun driven projectiles. The system can be compact, vacuum isolated, and ease of cooling. Conceptual design layout and parameter estimations are presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI060

Export •

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

THPRI076

Laser Triggered RF Breakdown Study Using an S-band Photocathode Gun

3943

J.H. Shao, W. Gai
ANL, Argonne, Illinois, USA
H.B. Chen, Y.-C. Du, W.-H. Huang, J. Shi, C.-X. Tang, L.X. Yan
TUB, Beijing, People's Republic of China
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
F.Y. Wang
SLAC, Menlo Park, California, USA

A laser triggered RF breakdown experiment was carried out with an S-band photocathode gun at Tsinghua University for attempting understanding of the RF breakdown processes. By systematic measurement of the time dependence of the breakdown current at the gun exit and the stored RF energy in the cavity, one might gain insight into the time evolution of RF breakdown physics. A correlation of the stored energy and field emission current has been analysed with an equivalent circuit model. Experimental details and analysis methods are reported.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI076

Export •

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

THPRI077

Electric Field Enhancement Study using an L-band Photocathode Gun

3946

J.H. Shao, W. Gai
ANL, Argonne, Illinois, USA
H.B. Chen, J. Shi
TUB, Beijing, People's Republic of China
C.-J. Jing
Euclid TechLabs, LLC, Solon, Ohio, USA
F.Y. Wang, L. Xiao
SLAC, Menlo Park, California, USA

RF breakdown in high gradient accelerating structures is a fundamental problem that is still needed better understanding. Past studies have indicated that field emission, which is usually represented by electric field enhancement (i.e. β) produced from the Fowler-Nordheim plot, is strongly coupled to the breakdown problem. A controlled surface study using a high gradient L-band RF gun is being carried out. With a flat cathode, the maximum electric field on the surface reached 10³ MV/m. And electric field as high as 565 MV/m on the surface was achieved by a pin-shaped cathode. The field enhancement factor was measured at different surface field during the conditioning process. Initial results of the study are presented in this paper.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2014-THPRI077

Export •

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