IPAC2019 - List of Authors (Li, D.)

Paper	Title	Page
TUPRB097	Recent Progress on the Design of Normal Conducting APEX-II VHF CW Electron Gun	1891
	D. Li, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, T.H. Luo, C.E. Mitchell, J. Qiang, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA H.Q. Feng TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 We report recent progress on the design of a normal conducting CW electron gun, APEX-II (Advanced Photo-injector EXperiment-II) at Lawrence Berkeley National Laboratory. APEX-II is an upgrade of the successful APEX gun and the LCLS-II (Linac Coherent Light Source-II) injector, aiming at applications for Free electron laser (FEL) such as LCLS-II High Energy upgrade, UED (Ultrafast Electron Diffraction) and UEM (Ultrafast Electron Microscopy). The APEX-II adopted a two-cell cavity design with resonant frequency of 162.5 MHz. The APEX-II gun is targeting to achieve exceeding 30 MV/m of launch gradient at the cathode and output energy above 1.5 MeV with transverse emittance of 0.1 um at 100 pC. Advanced MOGA optimization technique has been used for both the RF cavity design and extensive beam dynamics studies using APEX-like and LCLS-II like injector layout. Detailed RF designs, beam dynamics studies, preliminary engineering design and FEA analysis will be presented, with cavity features that were demonstrated to be crucial in the operation of the APEX gun.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPRB097
About •	paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPTS076	RF Design of APEX2 Cavities	2094
	T.H. Luo, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, D. Li, C.E. Mitchell, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA H.Q. Feng TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231 APEX2 is a proposed high repetition rate, high brightness electron source based on CW normal conducting RF cavities, aiming to further extend the brightness performance for FEL and UED/UEM beyond APEX. APEX2 consists of two cavities, one gun cavity for generating photo-electrons and one following cavity for beam energy boosting. In this paper, we present the RF design of the APEX2 cavities. The design has considered both beam dynamics requirements and engineering feasibility. A novel geometry optimization method with Genetic Algorithm has been implemented in the design procedure.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS076
About •	paper received ※ 15 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPTS080	Beam Dynamics Studies of an APEX2-Based Photoinjector	2109
	C.E. Mitchell, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, D. Li, T.H. Luo, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA
	APEX2 is a proposed normal conducting radio-frequency (RF) electron gun operating in the very high frequency (VHF) range in continuous wave (CW) mode, designed to drive applications that require both high beam brightness and high repetition rate, such as free electron lasers (such as LCLS-II-HE), ultra-fast electron diffraction, and microscopy. The gun consists of a two-cell RF cavity operating at 162.5 MHz with a cathode field of 34 MV/m, together with an embedded focusing solenoid. We study the beam dynamics in an APEX-II-based photoinjector (up to ~20 MeV), targeting a transverse 95% beam emittance of 0.1 um at 12.5 A peak current for the case of 100 pC charge for FEL applications. The high cathode field leads to enhanced beam brightness, while the increased gun exit energy of ~1.5 MeV reduces the effects of space charge, and possibly eliminates the need for an RF buncher. The embedded solenoid is designed to control the transverse beam size while minimizing emittance growth due to geometric aberrations. As a result, the transverse beam performance targets are achieved, and ongoing work will further optimize longitudinal beam quality for downstream FEL transport.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS080
About •	paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPRB080	Optimization of RF Cavities Using MOGA for ALS-U	3007
	H.Q. Feng, K.M. Baptiste, D. Li, T.H. Luo LBNL, Berkeley, California, USA H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 A multi-objective genetic algorithm-based optimiza-tion process has been applied to optimize the RF design of a 500 MHz main cavity and a 1.5 GHz Higher Harmon-ic Cavity (HHC) for the Advanced Light Source upgrade (ALS-U) in Lawrence Berkeley National Laboratory (LBNL). For the main cavity, a significant improvement, compared with the existing ALS cavity, has been achieved in cavity shunt impedance and power loss den-sity simultaneously. The field strengths and distribution of the optimized structure are analysed for further re-search. For the HHC, a cavity with low R/Q has been pre-liminary designed to mitigate the beam instability. This study also serves as an example of how a genetic algo-rithm can be used for optimizing RF cavities.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB080
About •	paper received ※ 16 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPRB081	Design Study on Higher Harmonic Cavity for ALS-U	3011
	H.Q. Feng, K.M. Baptiste, S. De Santis, D. Li, T.H. Luo LBNL, Berkeley, California, USA H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang TUB, Beijing, People’s Republic of China
	Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 The ALS upgrade (ALS-U) to a diffraction-limited light source [1] depends on the ability to lengthen the stored bunches to limit the emittance growth and increase the beam life time. Higher harmonic cavities (HHCs), also known as Landau cavities, have been proposed to in-crease beam lifetime and Landau damping by lengthen-ing the bunch. We present an optimized 1.5 GHz normal conducting HHC design for the ALS-U with a supercon-ducting-like geometry using multi-objective genetic algorithm (MOGA) for lower R/Q. The optimization goal is to reach the required shunt impedance while maintain-ing a relatively high Q value of the cavities. To minimize the coupled bunch instabilities, higher-order mode (HOM) of the HHC as well as corresponding impedance are explored and characterized.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB081
About •	paper received ※ 16 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPRB084	Mechanical Design and Analysis of the Proposed APEX2 VHF CW Electron Gun	3014
	A.R. Lambert, H.Q. Feng, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells LBNL, Berkeley, California, USA
	Funding: Work supported by the Office of Science, U.S. Department of Energy under DOE contract number DEAC02-05CH11231 Normal conducting radio-frequency (RF) guns resonating in the very high frequency (VHF) range (30-300 MHz) and operating in continuous wave (CW) mode have successfully achieved the targeted brightness and reliability necessary for upgrading the performance of current lower repetition rate accelerator-based instruments such as X-ray free electron lasers (FELs), and ultra-fast electron diffraction (UED) and microscopy (UEM). The APEX2 (Advanced Photo-injector Experiment 2) electron gun is a proposed upgrade for the current LCLS-II injector, which was based on the original APEX design. In contrast, APEX2 is designed as a two-cell cavity operating at 162.5 MHz with a launching field at the cathode equal to 34 MV/m, producing a beam energy of 1.5 to 2 MeV, more than double APEX. Operation of the gun in this condition will require upwards of 200 kW of RF power, thus proper thermal management is crucial to achieve target performance. This paper describes the current design, thermal performance and tuning methods.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB084
About •	paper received ※ 13 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Recent Progress on the Design of Normal Conducting APEX-II VHF CW Electron Gun

1891

D. Li, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, T.H. Luo, C.E. Mitchell, J. Qiang, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA
H.Q. Feng
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
We report recent progress on the design of a normal conducting CW electron gun, APEX-II (Advanced Photo-injector EXperiment-II) at Lawrence Berkeley National Laboratory. APEX-II is an upgrade of the successful APEX gun and the LCLS-II (Linac Coherent Light Source-II) injector, aiming at applications for Free electron laser (FEL) such as LCLS-II High Energy upgrade, UED (Ultrafast Electron Diffraction) and UEM (Ultrafast Electron Microscopy). The APEX-II adopted a two-cell cavity design with resonant frequency of 162.5 MHz. The APEX-II gun is targeting to achieve exceeding 30 MV/m of launch gradient at the cathode and output energy above 1.5 MeV with transverse emittance of 0.1 um at 100 pC. Advanced MOGA optimization technique has been used for both the RF cavity design and extensive beam dynamics studies using APEX-like and LCLS-II like injector layout. Detailed RF designs, beam dynamics studies, preliminary engineering design and FEA analysis will be presented, with cavity features that were demonstrated to be crucial in the operation of the APEX gun.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPRB097

About •

paper received ※ 15 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

Export •

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

TUPTS076

RF Design of APEX2 Cavities

2094

T.H. Luo, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, D. Li, C.E. Mitchell, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA
H.Q. Feng
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231
APEX2 is a proposed high repetition rate, high brightness electron source based on CW normal conducting RF cavities, aiming to further extend the brightness performance for FEL and UED/UEM beyond APEX. APEX2 consists of two cavities, one gun cavity for generating photo-electrons and one following cavity for beam energy boosting. In this paper, we present the RF design of the APEX2 cavities. The design has considered both beam dynamics requirements and engineering feasibility. A novel geometry optimization method with Genetic Algorithm has been implemented in the design procedure.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS076

About •

paper received ※ 15 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

Export •

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

TUPTS080

Beam Dynamics Studies of an APEX2-Based Photoinjector

2109

C.E. Mitchell, H.Q. Feng, D. Filippetto, M.J. Johnson, A.R. Lambert, D. Li, T.H. Luo, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA

APEX2 is a proposed normal conducting radio-frequency (RF) electron gun operating in the very high frequency (VHF) range in continuous wave (CW) mode, designed to drive applications that require both high beam brightness and high repetition rate, such as free electron lasers (such as LCLS-II-HE), ultra-fast electron diffraction, and microscopy. The gun consists of a two-cell RF cavity operating at 162.5 MHz with a cathode field of 34 MV/m, together with an embedded focusing solenoid. We study the beam dynamics in an APEX-II-based photoinjector (up to ~20 MeV), targeting a transverse 95% beam emittance of 0.1 um at 12.5 A peak current for the case of 100 pC charge for FEL applications. The high cathode field leads to enhanced beam brightness, while the increased gun exit energy of ~1.5 MeV reduces the effects of space charge, and possibly eliminates the need for an RF buncher. The embedded solenoid is designed to control the transverse beam size while minimizing emittance growth due to geometric aberrations. As a result, the transverse beam performance targets are achieved, and ongoing work will further optimize longitudinal beam quality for downstream FEL transport.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-TUPTS080

About •

paper received ※ 14 May 2019 paper accepted ※ 23 May 2019 issue date ※ 21 June 2019

Export •

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

WEPRB080

Optimization of RF Cavities Using MOGA for ALS-U

3007

H.Q. Feng, K.M. Baptiste, D. Li, T.H. Luo
LBNL, Berkeley, California, USA
H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
A multi-objective genetic algorithm-based optimiza-tion process has been applied to optimize the RF design of a 500 MHz main cavity and a 1.5 GHz Higher Harmon-ic Cavity (HHC) for the Advanced Light Source upgrade (ALS-U) in Lawrence Berkeley National Laboratory (LBNL). For the main cavity, a significant improvement, compared with the existing ALS cavity, has been achieved in cavity shunt impedance and power loss den-sity simultaneously. The field strengths and distribution of the optimized structure are analysed for further re-search. For the HHC, a cavity with low R/Q has been pre-liminary designed to mitigate the beam instability. This study also serves as an example of how a genetic algo-rithm can be used for optimizing RF cavities.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB080

About •

paper received ※ 16 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

Export •

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

WEPRB081

Design Study on Higher Harmonic Cavity for ALS-U

3011

H.Q. Feng, K.M. Baptiste, S. De Santis, D. Li, T.H. Luo
LBNL, Berkeley, California, USA
H.Q. Feng, W.-H. Huang, Z.N. Liu, C.-X. Tang
TUB, Beijing, People’s Republic of China

Funding: Director of Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
The ALS upgrade (ALS-U) to a diffraction-limited light source [1] depends on the ability to lengthen the stored bunches to limit the emittance growth and increase the beam life time. Higher harmonic cavities (HHCs), also known as Landau cavities, have been proposed to in-crease beam lifetime and Landau damping by lengthen-ing the bunch. We present an optimized 1.5 GHz normal conducting HHC design for the ALS-U with a supercon-ducting-like geometry using multi-objective genetic algorithm (MOGA) for lower R/Q. The optimization goal is to reach the required shunt impedance while maintain-ing a relatively high Q value of the cavities. To minimize the coupled bunch instabilities, higher-order mode (HOM) of the HHC as well as corresponding impedance are explored and characterized.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB081

About •

paper received ※ 16 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

Export •

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

WEPRB084

Mechanical Design and Analysis of the Proposed APEX2 VHF CW Electron Gun

3014

A.R. Lambert, H.Q. Feng, D. Filippetto, M.J. Johnson, D. Li, T.H. Luo, C.E. Mitchell, F. Sannibale, J.W. Staples, S.P. Virostek, R.P. Wells
LBNL, Berkeley, California, USA

Funding: Work supported by the Office of Science, U.S. Department of Energy under DOE contract number DEAC02-05CH11231
Normal conducting radio-frequency (RF) guns resonating in the very high frequency (VHF) range (30-300 MHz) and operating in continuous wave (CW) mode have successfully achieved the targeted brightness and reliability necessary for upgrading the performance of current lower repetition rate accelerator-based instruments such as X-ray free electron lasers (FELs), and ultra-fast electron diffraction (UED) and microscopy (UEM). The APEX2 (Advanced Photo-injector Experiment 2) electron gun is a proposed upgrade for the current LCLS-II injector, which was based on the original APEX design. In contrast, APEX2 is designed as a two-cell cavity operating at 162.5 MHz with a launching field at the cathode equal to 34 MV/m, producing a beam energy of 1.5 to 2 MeV, more than double APEX. Operation of the gun in this condition will require upwards of 200 kW of RF power, thus proper thermal management is crucial to achieve target performance. This paper describes the current design, thermal performance and tuning methods.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPRB084

About •

paper received ※ 13 May 2019 paper accepted ※ 18 May 2019 issue date ※ 21 June 2019

Export •

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