IPAC2018 - List of Authors (Wu, J.)

Paper	Title	Page
THPMK016	Simulation Study of the NSRRC High Brightness Linac System and Free Electron Laser	4329
	W.K. Lau, C.H. Chen, H.P. Hsueh, N.Y. Huang NSRRC, Hsinchu, Taiwan J. Wu SLAC, Menlo Park, California, USA
	A 263 MeV linac system has been designed to provide a high brightness electron beam for the NSRRC VUV FEL test facility. This system is equipped with a dogleg with linearization optics to compensate the effects of nonlinear energy chirps introduced into the system by the chirper linac voltage during bunch compression. In this study, we performed start-to-end simulation to illustrate the capability of this linac system to generate a beam that can be used to drive a SASE FEL to saturation within reasonable undulator length. It has been demonstrated that, for a 200 pC beam, such FEL has a saturated output power of ~200 MW at 6-m undulator length. Further optimization of bunch current profile and momentum spectrum is required.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK016
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK051	Theoretical Formulation of Improved SASE FEL Based on Slippage Enhancement Scheme	4398
	C.-Y. Tsai, J. Wu, C. Yang, G. Zhou SLAC, Menlo Park, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea G. Zhou IHEP, Beijing, People's Republic of China
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164. A method to improve the spectral brightness of self-amplified spontaneous emission (SASE) based on slippage enhancement has been proposed, . The implementation is to insert a series of magnetic chicanes to introduce a path-length delay of the electron beam to the radiation beam. By correlating the electron slices of neighboring cooperation distances this can lengthen the collective interaction and thus enhance the spectral brightness. In the existing literature most studies rely on numerical simulations and there is limited work on analytical analysis. In this paper we formulate the problem of slippage enhanced SASE (SeSASE) high-gain FEL with inclusion of by-pass magnetic chicanes. The analysis takes the finite energy spread of the electron beam and the nonzero momentum compaction of the chicane into consideration. The evolution of spectral bandwidth of SeSASE is compared with that of usual SASE in theory and numerical simulations. The effects of finite beam energy spread and non-isochronisity are also quantified. J. Wu et al., FEL2012 **B. W. J. McNeil et al., PRL 110, 134802 (2013)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK051
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK052	Numerical Simulation of Phase-Shift Method for Fel Power Enhancement in PAL-XFEL	4402
	C.-Y. Tsai, J. Wu, C. Yang, G. Zhou SLAC, Menlo Park, California, USA H.-S. Kang PAL, Pohang, Kyungbuk, Republic of Korea M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea G. Zhou IHEP, Beijing, People's Republic of China
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164. Recently the phase jump method for efficiency enhancement in free-electron laser (FEL) was proposed. One of the unique features of PAL-XFEL with phase shifters may be taken for the experimental demonstration of this phase jump scheme. In this paper we numerically investigate the scheme using the three-dimensional numerical simulation code GENESIS. The physical parameters are based on hard x-ray line of PAL-XFEL*. The preliminary simulation results indicate that this potential phase jump scheme can enhance at least one order of magnitude of FEL power performance. Combination of this scheme with undulator tapering is also discussed in this paper. A. Mak, F. Curbis, and S. Werin, PRAB 20, 060703 (2017) S. Rieche, NIMA 429(1):243-248 (1999) *I. S. Ko et al., Appl. Sci. 2017, 7, 479 (2017)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK052
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK053	Simulation for LCLS-II Hard X-ray Self Seeding Scheme	4406
	C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou SLAC, Menlo Park, California, USA H.X. Deng SINAP, Shanghai, People's Republic of China D.H. He USTC/NSRL, Hefei, Anhui, People's Republic of China Y. Hong, B. Yang University of Texas at Arlington, Arlington, USA X.F. Wang CIAE, Beijing, People's Republic of China M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea G. Zhou IHEP, Beijing, People's Republic of China
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Oﬃce of Science Early Career Research Program grant FWP-2013-SLAC-100164. Typical SASE FELs have poor temporal coherence because of starting from shot noise. Self-seeding scheme is an approach to improve the longitudinal coherence. The single crystal monochromator self-seeding has been in successful operation in LCLS. For the high repetition rate LCLS-II machine, for damage consideration, it was initially proposed to have a two-stage self-seeding scheme, yet we have found the two-stage self-seeding scheme has no advantage over one-stage self-seeding scheme. In this paper, we investigate the optimal self-seeding conﬁguration of LCLS-II for different photon energies, and present a comparison between one-stage and two-stage self-seeding scheme of LCLS-II.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK053
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK054	Analysis of 1D FEL Sideband Instability with Inclusion of Energy Detune and Space Charge	4410
	C.-Y. Tsai, J. Wu, C. Yang, G. Zhou SLAC, Menlo Park, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164. It has been known that free-electron laser (FEL) is capable of generating a coherent high-power radiation over a broad spectrum. Recently there is a great interest in pursuing higher peak power (for example, at terawatt level) in FEL that can enable coherent diffraction imaging and probe fundamental high-field physics. The FEL radiation power can be increased by virtue of undulator tapering. However the FEL sideband signal begins to exponentially grow in the post-saturation regime. In this paper we extend our sideband analysis* by including both the energy detune due to discrete undulator tapering and longitudinal space charge in an effective 1-D model. A dispersion relation with explicit energy detune and space charge is derived. The study is carried out semi-analytically and compared with simulations. The impact of energy detune and space charge is analyzed. * C.-Y. Tsai et al., Analysis of the sideband instability based on a one-dimensional high-gain free electron laser model, PRAB (accepted)
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK054
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK055	Self Seeding Scheme for LCLS-II-HE	4414
	C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou SLAC, Menlo Park, California, USA H.X. Deng, X.F. Wang SINAP, Shanghai, People's Republic of China D.H. He USTC/NSRL, Hefei, Anhui, People's Republic of China Y. Hong, B. Yang University of Texas at Arlington, Arlington, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea G. Zhou IHEP, Beijing, People's Republic of China
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Oﬃce of Science Early Career Research Program grant FWP-2013-SLAC-100164. Self-seeding is a reliable approach to generate fully coherent FEL pulses. Hard X-ray self-seeding can be realized by using a single crystal in Bragg transmission geometry. However, for a high repetition rate machine, the heat load on the crystal may become an issue. In this paper, we will study the facility performance of LCLS-II-HE by numerical simulations, and discuss the heat load and optimal undulator baseline conﬁguration of LCLS-II-HE self-seeding scheme, and study the emittance tolerance of the LCLS-II-HE.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK055
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMK056	Effect of Transverse Radiation Defocusing in Post-Saturation Regime of High-Gain X-Ray Free-Electron Laser	4418
	C.-Y. Tsai, J. Wu, C. Yang, G. Zhou SLAC, Menlo Park, California, USA M. Yoon POSTECH, Pohang, Kyungbuk, Republic of Korea G. Zhou IHEP, Beijing, People's Republic of China
	Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164. When untapered high-gain free electron laser (FEL) reaches saturation, the exponential growth ceases and the radiation power starts to oscillate about an equilibrium. For a high-gain tapered FEL, although the power is enhanced after the first saturation, it is known that there is a so-called second saturation point where the FEL power growth stops. In addition to the sideband instability, lack of transverse radiation focusing in the post-saturation regime can be another major reason leading to occurrence of the second saturation. In this paper we study the transverse diffraction effect and its impact on tapered FEL in the post-saturation regime. The study is carried out analytically together with three-dimensional numerical simulation. The numerical parameters are taken from LCLS-like electron beam and undulator system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK056
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Simulation Study of the NSRRC High Brightness Linac System and Free Electron Laser

4329

W.K. Lau, C.H. Chen, H.P. Hsueh, N.Y. Huang
NSRRC, Hsinchu, Taiwan
J. Wu
SLAC, Menlo Park, California, USA

A 263 MeV linac system has been designed to provide a high brightness electron beam for the NSRRC VUV FEL test facility. This system is equipped with a dogleg with linearization optics to compensate the effects of nonlinear energy chirps introduced into the system by the chirper linac voltage during bunch compression. In this study, we performed start-to-end simulation to illustrate the capability of this linac system to generate a beam that can be used to drive a SASE FEL to saturation within reasonable undulator length. It has been demonstrated that, for a 200 pC beam, such FEL has a saturated output power of ~200 MW at 6-m undulator length. Further optimization of bunch current profile and momentum spectrum is required.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK016

Export •

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

THPMK051

Theoretical Formulation of Improved SASE FEL Based on Slippage Enhancement Scheme

4398

C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
SLAC, Menlo Park, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea
G. Zhou
IHEP, Beijing, People's Republic of China

Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
A method to improve the spectral brightness of self-amplified spontaneous emission (SASE) based on slippage enhancement has been proposed*, **. The implementation is to insert a series of magnetic chicanes to introduce a path-length delay of the electron beam to the radiation beam. By correlating the electron slices of neighboring cooperation distances this can lengthen the collective interaction and thus enhance the spectral brightness. In the existing literature most studies rely on numerical simulations and there is limited work on analytical analysis. In this paper we formulate the problem of slippage enhanced SASE (SeSASE) high-gain FEL with inclusion of by-pass magnetic chicanes. The analysis takes the finite energy spread of the electron beam and the nonzero momentum compaction of the chicane into consideration. The evolution of spectral bandwidth of SeSASE is compared with that of usual SASE in theory and numerical simulations. The effects of finite beam energy spread and non-isochronisity are also quantified.
*J. Wu et al., FEL2012
**B. W. J. McNeil et al., PRL 110, 134802 (2013)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK051

Export •

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

THPMK052

Numerical Simulation of Phase-Shift Method for Fel Power Enhancement in PAL-XFEL

4402

C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
SLAC, Menlo Park, California, USA
H.-S. Kang
PAL, Pohang, Kyungbuk, Republic of Korea
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea
G. Zhou
IHEP, Beijing, People's Republic of China

Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Recently the phase jump method for efficiency enhancement in free-electron laser (FEL) was proposed*. One of the unique features of PAL-XFEL with phase shifters may be taken for the experimental demonstration of this phase jump scheme. In this paper we numerically investigate the scheme using the three-dimensional numerical simulation code GENESIS**. The physical parameters are based on hard x-ray line of PAL-XFEL***. The preliminary simulation results indicate that this potential phase jump scheme can enhance at least one order of magnitude of FEL power performance. Combination of this scheme with undulator tapering is also discussed in this paper.
*A. Mak, F. Curbis, and S. Werin, PRAB 20, 060703 (2017)
**S. Rieche, NIMA 429(1):243-248 (1999)
***I. S. Ko et al., Appl. Sci. 2017, 7, 479 (2017)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK052

Export •

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

THPMK053

Simulation for LCLS-II Hard X-ray Self Seeding Scheme

4406

C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou
SLAC, Menlo Park, California, USA
H.X. Deng
SINAP, Shanghai, People's Republic of China
D.H. He
USTC/NSRL, Hefei, Anhui, People's Republic of China
Y. Hong, B. Yang
University of Texas at Arlington, Arlington, USA
X.F. Wang
CIAE, Beijing, People's Republic of China
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea
G. Zhou
IHEP, Beijing, People's Republic of China

Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Oﬃce of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Typical SASE FELs have poor temporal coherence because of starting from shot noise. Self-seeding scheme is an approach to improve the longitudinal coherence. The single crystal monochromator self-seeding has been in successful operation in LCLS. For the high repetition rate LCLS-II machine, for damage consideration, it was initially proposed to have a two-stage self-seeding scheme, yet we have found the two-stage self-seeding scheme has no advantage over one-stage self-seeding scheme. In this paper, we investigate the optimal self-seeding conﬁguration of LCLS-II for different photon energies, and present a comparison between one-stage and two-stage self-seeding scheme of LCLS-II.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK053

Export •

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

THPMK054

Analysis of 1D FEL Sideband Instability with Inclusion of Energy Detune and Space Charge

4410

C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
SLAC, Menlo Park, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea

Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
It has been known that free-electron laser (FEL) is capable of generating a coherent high-power radiation over a broad spectrum. Recently there is a great interest in pursuing higher peak power (for example, at terawatt level) in FEL that can enable coherent diffraction imaging and probe fundamental high-field physics. The FEL radiation power can be increased by virtue of undulator tapering. However the FEL sideband signal begins to exponentially grow in the post-saturation regime. In this paper we extend our sideband analysis* by including both the energy detune due to discrete undulator tapering and longitudinal space charge in an effective 1-D model. A dispersion relation with explicit energy detune and space charge is derived. The study is carried out semi-analytically and compared with simulations. The impact of energy detune and space charge is analyzed.
* C.-Y. Tsai et al., Analysis of the sideband instability based on a one-dimensional high-gain free electron laser model, PRAB (accepted)

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK054

Export •

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

THPMK055

Self Seeding Scheme for LCLS-II-HE

4414

C. Yang, Y. Feng, J. Krzywinski, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou
SLAC, Menlo Park, California, USA
H.X. Deng, X.F. Wang
SINAP, Shanghai, People's Republic of China
D.H. He
USTC/NSRL, Hefei, Anhui, People's Republic of China
Y. Hong, B. Yang
University of Texas at Arlington, Arlington, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea
G. Zhou
IHEP, Beijing, People's Republic of China

Funding: The work was supported by the US Department of Energy (DOE) under contract DE-AC02-76SF00515 and the US DOE Oﬃce of Science Early Career Research Program grant FWP-2013-SLAC-100164.
Self-seeding is a reliable approach to generate fully coherent FEL pulses. Hard X-ray self-seeding can be realized by using a single crystal in Bragg transmission geometry. However, for a high repetition rate machine, the heat load on the crystal may become an issue. In this paper, we will study the facility performance of LCLS-II-HE by numerical simulations, and discuss the heat load and optimal undulator baseline conﬁguration of LCLS-II-HE self-seeding scheme, and study the emittance tolerance of the LCLS-II-HE.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK055

Export •

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

THPMK056

Effect of Transverse Radiation Defocusing in Post-Saturation Regime of High-Gain X-Ray Free-Electron Laser

4418

C.-Y. Tsai, J. Wu, C. Yang, G. Zhou
SLAC, Menlo Park, California, USA
M. Yoon
POSTECH, Pohang, Kyungbuk, Republic of Korea
G. Zhou
IHEP, Beijing, People's Republic of China

Funding: The work was supported by the US Department of Energy (DOE) under contract DE- AC02-76SF00515 and the US DOE Office of Science Early Career Research Program grant FWP-2013-SLAC-100164.
When untapered high-gain free electron laser (FEL) reaches saturation, the exponential growth ceases and the radiation power starts to oscillate about an equilibrium. For a high-gain tapered FEL, although the power is enhanced after the first saturation, it is known that there is a so-called second saturation point where the FEL power growth stops. In addition to the sideband instability, lack of transverse radiation focusing in the post-saturation regime can be another major reason leading to occurrence of the second saturation. In this paper we study the transverse diffraction effect and its impact on tapered FEL in the post-saturation regime. The study is carried out analytically together with three-dimensional numerical simulation. The numerical parameters are taken from LCLS-like electron beam and undulator system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPMK056

Export •

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