IPAC2018 - List of Authors (Gao, Q.)

Paper	Title	Page
TUPMF020	Demonstration of Fast, Single-shot Photocathode QE Mapping Method Using MLA Pattern Beam	1293
	E.E. Wisniewski, M.E. Conde, D.S. Doran, W. Gai, Q. Gao, W. Liu, J.G. Power, C. Whiteford ANL, Argonne, Illinois, USA Q. Gao TUB, Beijing, People's Republic of China G. Ha PAL, Pohang, Republic of Korea A. Halavanau, P. Piot Northern Illinois University, DeKalb, Illinois, USA P. Piot Fermilab, Batavia, Illinois, USA
	Funding: UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S.A. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. Quantum efficiency (QE) is the chief figure of merit in the characterization of photocathodes. Semiconductor photocathodes, especially when used in high rep-rate photo-injectors, are known to show QE degradation over time and must be replaced. The total QE is the basic diagnostic which is used widely and is easy to obtain. However, a QE map indicating variations of QE across the cathode surface has greater utility. It can quickly diagnose problems of QE inhomogeneity. Most QE mapping techniques require hours to complete and are thus disruptive to a user facility schedule. A fast, single-shot method has been proposed (citation) using a micro-lens array (MLA) generated QE map. In this paper we report the implementation of the method at Argonne Wakefield Accelerator facility. A micro-lens array (MLA) is used to project an array of beamlets onto the photocathode. The resulting photoelectron beam in the form of an array of electron beamlets is imaged at a YAG screen. Four synchronized measurements are made and the results used to produce a QE map of the photocathode.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF020
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THPML012	Simulations and Measurements of the Wakefield Loading Effect in Argonne Wakefield Accelerator Beamline	4675
	J. Upadhyay, E.I. Simakov LANL, Los Alamos, New Mexico, USA M.E. Conde, Q. Gao, N.R. Neveu, J.G. Power, J.H. Shao, E.E. Wisniewski ANL, Argonne, Illinois, USA N.R. Neveu IIT, Chicago, Illinois, USA
	A beam driven acceleration experiment in a photonic band gap (PBG) structure is planned at Argonne wakefied accelerator (AWA) facility at Argonne National Laboratory. We plan to pass a high charge (drive) beam through a travelling wave 11.7 GHz PBG structure and generate a wakefield. This wakefield will be probed by a low charge (witness) beam to demonstrate wakefield acceleration and deceleration. The drive and witness bunches will be accelerated to above 60 MeV in the main accelerator at AWA which has frequency of 1.3 GHz. The charges used in this experiment could be as high as 20 nC. To measure the exclusive effect of PBG the structure on acceleration and deceleration of the witness bunch we have to exclude the effect of beam loading of the main AWA accelerator structure. To understand the wakefield effect in AWA, we conducted an experiment where we passed the high charge (10 nC) beam through the accelerator structure which was followed by a 2 nC witness beam separated by 4 wavelength. The energy of witness beam was measured in the presence and absence of the drive beam. The beam loading was observed and quantified. The results of this work will be presented in the conference.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML012
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THPML013	Demonstration of the Wakefield Acceleration in an 11.7 GHz Photonic Band Gap Accelerator Structure	4678
	J. Upadhyay, E.I. Simakov LANL, Los Alamos, New Mexico, USA M.E. Conde, Q. Gao, N.R. Neveu, J.G. Power, J.H. Shao, E.E. Wisniewski ANL, Argonne, Illinois, USA
	We plan to conduct a beam driven acceleration experiment in a photonic band gap (PBG) accelerator structure operating at 11.7 GHz at Argonne Wakefield Accelerator (AWA) facility. For the experiment, the PBG structure will be excited by a high charge (up to 10 nC) electron bunch, and a second smaller charge witness bunch will be accelerated. Because the PBG structure was fabricated with electroforming, the AWA beamline includes a Be window placed before the PBG structure that protects the cathode from contamination due to possible outgassing from the electroformed copper. The diameter of the Be window is 9 mm and the beam tube diameter of the PBG structure is 6.4 mm. The size of the high charge electron beam on Be window has to be minimized to minimize scattering. The parameters of the beamline had to be adjusted to achieve good propagation of the beam. An OPAL simulation for the AWA beamline was performed for 1, 5, and 10 nC beams. The beam size was experimentally measured at different positions in the beamline for different charges to verify simulations. Finally, the high charge electron beam was passed through the PBG structure and acceleration of the witness bunch was measured
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML013
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Paper

Title

Page

Demonstration of Fast, Single-shot Photocathode QE Mapping Method Using MLA Pattern Beam

1293

E.E. Wisniewski, M.E. Conde, D.S. Doran, W. Gai, Q. Gao, W. Liu, J.G. Power, C. Whiteford
ANL, Argonne, Illinois, USA
Q. Gao
TUB, Beijing, People's Republic of China
G. Ha
PAL, Pohang, Republic of Korea
A. Halavanau, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
P. Piot
Fermilab, Batavia, Illinois, USA

Funding: UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S.A. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357.
Quantum efficiency (QE) is the chief figure of merit in the characterization of photocathodes. Semiconductor photocathodes, especially when used in high rep-rate photo-injectors, are known to show QE degradation over time and must be replaced. The total QE is the basic diagnostic which is used widely and is easy to obtain. However, a QE map indicating variations of QE across the cathode surface has greater utility. It can quickly diagnose problems of QE inhomogeneity. Most QE mapping techniques require hours to complete and are thus disruptive to a user facility schedule. A fast, single-shot method has been proposed (citation) using a micro-lens array (MLA) generated QE map. In this paper we report the implementation of the method at Argonne Wakefield Accelerator facility. A micro-lens array (MLA) is used to project an array of beamlets onto the photocathode. The resulting photoelectron beam in the form of an array of electron beamlets is imaged at a YAG screen. Four synchronized measurements are made and the results used to produce a QE map of the photocathode.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPMF020

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THPML012

Simulations and Measurements of the Wakefield Loading Effect in Argonne Wakefield Accelerator Beamline

4675

J. Upadhyay, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
M.E. Conde, Q. Gao, N.R. Neveu, J.G. Power, J.H. Shao, E.E. Wisniewski
ANL, Argonne, Illinois, USA
N.R. Neveu
IIT, Chicago, Illinois, USA

A beam driven acceleration experiment in a photonic band gap (PBG) structure is planned at Argonne wakefied accelerator (AWA) facility at Argonne National Laboratory. We plan to pass a high charge (drive) beam through a travelling wave 11.7 GHz PBG structure and generate a wakefield. This wakefield will be probed by a low charge (witness) beam to demonstrate wakefield acceleration and deceleration. The drive and witness bunches will be accelerated to above 60 MeV in the main accelerator at AWA which has frequency of 1.3 GHz. The charges used in this experiment could be as high as 20 nC. To measure the exclusive effect of PBG the structure on acceleration and deceleration of the witness bunch we have to exclude the effect of beam loading of the main AWA accelerator structure. To understand the wakefield effect in AWA, we conducted an experiment where we passed the high charge (10 nC) beam through the accelerator structure which was followed by a 2 nC witness beam separated by 4 wavelength. The energy of witness beam was measured in the presence and absence of the drive beam. The beam loading was observed and quantified. The results of this work will be presented in the conference.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML012

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

THPML013

Demonstration of the Wakefield Acceleration in an 11.7 GHz Photonic Band Gap Accelerator Structure

4678

J. Upadhyay, E.I. Simakov
LANL, Los Alamos, New Mexico, USA
M.E. Conde, Q. Gao, N.R. Neveu, J.G. Power, J.H. Shao, E.E. Wisniewski
ANL, Argonne, Illinois, USA

We plan to conduct a beam driven acceleration experiment in a photonic band gap (PBG) accelerator structure operating at 11.7 GHz at Argonne Wakefield Accelerator (AWA) facility. For the experiment, the PBG structure will be excited by a high charge (up to 10 nC) electron bunch, and a second smaller charge witness bunch will be accelerated. Because the PBG structure was fabricated with electroforming, the AWA beamline includes a Be window placed before the PBG structure that protects the cathode from contamination due to possible outgassing from the electroformed copper. The diameter of the Be window is 9 mm and the beam tube diameter of the PBG structure is 6.4 mm. The size of the high charge electron beam on Be window has to be minimized to minimize scattering. The parameters of the beamline had to be adjusted to achieve good propagation of the beam. An OPAL simulation for the AWA beamline was performed for 1, 5, and 10 nC beams. The beam size was experimentally measured at different positions in the beamline for different charges to verify simulations. Finally, the high charge electron beam was passed through the PBG structure and acceleration of the witness bunch was measured

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPML013

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