FEL2017 - List of Authors (Yoon, M.)

Paper	Title	Page
MOP020	Sideband Instability in a Tapered Free Electron Laser	76
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA J. Wu, C. Yang 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. For a high-gain tapered free electron laser (FEL), it is known that there is a so-called second saturation point where the FEL power growth stops. Sideband instability is one of the major reasons leading to this second-saturation and thus prevents reaching terawatt-level power output in an X-ray FEL. It is believed that a strong taper can effectively suppress the sideband instability and further improve the efficiency and peak power. In this paper, we give quantitative analysis on the necessary taper gradient to minimize the sideband growth. We also discuss the transverse effects of induced electron de-trapping which is yet another major reason for the occurrence of the second-saturation point even with a strong enough taper. The study is carried out analytically together with numerical simulation. The numerical parameters are taken from LCLS-II type electron bunch and undulator system.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP020
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MOP021	Sideband Suppression in Tapered Free Electron Lasers	80
	C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA J. Wu, C. Yang 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. It is known that in a high-gain tapered free electron laser, there is the so-called second saturation point where the FEL power ceases to grow. Sideband instability is one of the major reasons causing this second saturation. Electron synchrotron oscillation coupling to the wideband SASE radiation leads to the appearance of sidebands in the FEL spectrum, and is believed to prevent a self-seeding tapered FEL from reaching very high peak power. A strong seed together with a fresh electron bunch or a fresh slice in conjunction with strong tapering of undulators can effectively suppress the sideband instability. In this paper, we give quantitative analysis on the necessary seed power as well as undulator tapering to minimize the sideband effects. The study is carried out semi-analytically together with numerical simulation. The machine and electron bunch parameters are chosen as those of PAL-XFEL and LCLS-II.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP021
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TUP057	Measurement of Short-Wavelength High-Gain FEL Temporal Coherence Length by a Phase Shifter	344
	G. Zhou IHEP, Beijing, People's Republic of China W. Liu USTC/NSRL, Hefei, Anhui, People's Republic of China W. Qin, T.O. Raubenheimer, J. Wu, C. Yang SLAC, Menlo Park, California, USA C.-Y. Tsai Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA B. Yang University of Texas at Arlington, Arlington, 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. Short-wavelength high-gain free-electron lasers (FELs) are now well established as a source of ultra-fast, ultra-brightness, longitudinally partial coherent light. Since coherence is one of the fundamental properties of light source, so continual effort is devoted to high-gain free-electron laser coherence measurements. In this work, we propose a possible approach, employing a phase shifter to induce electron beam delay to measure the temporal coherence length. Simple analysis, numerical simulation and preliminary experimental results are presented. This approach can be robust and independent of frequency.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP057
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MOP018	Distributed Self-Seeding Scheme for LCLS-II	68
	C. Yang, Y. Feng, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou SLAC, Menlo Park, California, USA B. Yang University of Texas at Arlington, Arlington, USA
	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 successful approach for generating high-brightness x-ray free electron laser (XFEL). A single-crystal monochromator in-between the undulator sections to generate a coherent seed is adopted in LCLS. However, for a high-repetition rate machine like LCLS-II, the crystal monochromator in current setup cannot sustain the high average power; hence a distributed self-seeding scheme utilizing multi-stages is necessary. Based on the criteria set on the crystal, the maximum allowed x-ray energy deposited in the crystal will determine the machine configuration for such a distributed self-seeding scheme. In this paper, a distributed self-seeding configuration is optimized for LCLS-II type projects in the hard x-ray FEL energy regime. The study is carried out based on numerical simulation.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP018
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TUP058	Slippage-Enhanced SASE FEL	348
	J. Wu, A. Brachmann, K. Fang, A. Marinelli, C. Pellegrini, T.O. Raubenheimer, C.-Y. Tsai, C. Yang, M. Yoon, G. Zhou SLAC, Menlo Park, California, USA H.-S. Kang, G. Kim, I.H. Nam PAL, Pohang, Republic of Korea B. Yang University of Texas at Arlington, Arlington, USA
	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. High-brightness XFEL is demanding for many users, in particular for certain types of imaging applications. Seeded FELs including self-seeding XFELs were successfully demonstrated. Alternative approaches by enhancing slippage between the x-ray pulse and the electron bunch were also demonstrated. This class of Slippage-enhanced SASE (SeSASE) schemes can be unique for FEL spectral range between 1.5 keV to 4 keV where neither grating-based soft x-ray self-seeding nor crystal-based hard x-ray self-seeding can easily access. SeSASE can provide high-brightness XFEL for high repetition rate machines not suffering from heat load on the crystal monochromator. We report start-to-end simulation results for LCLS-II project and PAL-XFEL project with study on tolerance. Performance comparison between SaSASE FEL and self-seeding FEL in the overlapping frequency range is also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP058
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Paper

Title

Page

Sideband Instability in a Tapered Free Electron Laser

76

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
J. Wu, C. Yang
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.
For a high-gain tapered free electron laser (FEL), it is known that there is a so-called second saturation point where the FEL power growth stops. Sideband instability is one of the major reasons leading to this second-saturation and thus prevents reaching terawatt-level power output in an X-ray FEL. It is believed that a strong taper can effectively suppress the sideband instability and further improve the efficiency and peak power. In this paper, we give quantitative analysis on the necessary taper gradient to minimize the sideband growth. We also discuss the transverse effects of induced electron de-trapping which is yet another major reason for the occurrence of the second-saturation point even with a strong enough taper. The study is carried out analytically together with numerical simulation. The numerical parameters are taken from LCLS-II type electron bunch and undulator system.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP020

Export •

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

MOP021

Sideband Suppression in Tapered Free Electron Lasers

80

C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
J. Wu, C. Yang
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.
It is known that in a high-gain tapered free electron laser, there is the so-called second saturation point where the FEL power ceases to grow. Sideband instability is one of the major reasons causing this second saturation. Electron synchrotron oscillation coupling to the wideband SASE radiation leads to the appearance of sidebands in the FEL spectrum, and is believed to prevent a self-seeding tapered FEL from reaching very high peak power. A strong seed together with a fresh electron bunch or a fresh slice in conjunction with strong tapering of undulators can effectively suppress the sideband instability. In this paper, we give quantitative analysis on the necessary seed power as well as undulator tapering to minimize the sideband effects. The study is carried out semi-analytically together with numerical simulation. The machine and electron bunch parameters are chosen as those of PAL-XFEL and LCLS-II.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP021

Export •

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

TUP057

Measurement of Short-Wavelength High-Gain FEL Temporal Coherence Length by a Phase Shifter

344

G. Zhou
IHEP, Beijing, People's Republic of China
W. Liu
USTC/NSRL, Hefei, Anhui, People's Republic of China
W. Qin, T.O. Raubenheimer, J. Wu, C. Yang
SLAC, Menlo Park, California, USA
C.-Y. Tsai
Virginia Polytechnic Institute and State University, Blacksburg, Virginia, USA
B. Yang
University of Texas at Arlington, Arlington, 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.
Short-wavelength high-gain free-electron lasers (FELs) are now well established as a source of ultra-fast, ultra-brightness, longitudinally partial coherent light. Since coherence is one of the fundamental properties of light source, so continual effort is devoted to high-gain free-electron laser coherence measurements. In this work, we propose a possible approach, employing a phase shifter to induce electron beam delay to measure the temporal coherence length. Simple analysis, numerical simulation and preliminary experimental results are presented. This approach can be robust and independent of frequency.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP057

Export •

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

MOP018

Distributed Self-Seeding Scheme for LCLS-II

68

C. Yang, Y. Feng, T.O. Raubenheimer, C.-Y. Tsai, J. Wu, M. Yoon, G. Zhou
SLAC, Menlo Park, California, USA
B. Yang
University of Texas at Arlington, Arlington, USA

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 successful approach for generating high-brightness x-ray free electron laser (XFEL). A single-crystal monochromator in-between the undulator sections to generate a coherent seed is adopted in LCLS. However, for a high-repetition rate machine like LCLS-II, the crystal monochromator in current setup cannot sustain the high average power; hence a distributed self-seeding scheme utilizing multi-stages is necessary. Based on the criteria set on the crystal, the maximum allowed x-ray energy deposited in the crystal will determine the machine configuration for such a distributed self-seeding scheme. In this paper, a distributed self-seeding configuration is optimized for LCLS-II type projects in the hard x-ray FEL energy regime. The study is carried out based on numerical simulation.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-MOP018

Export •

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

TUP058

Slippage-Enhanced SASE FEL

348

J. Wu, A. Brachmann, K. Fang, A. Marinelli, C. Pellegrini, T.O. Raubenheimer, C.-Y. Tsai, C. Yang, M. Yoon, G. Zhou
SLAC, Menlo Park, California, USA
H.-S. Kang, G. Kim, I.H. Nam
PAL, Pohang, Republic of Korea
B. Yang
University of Texas at Arlington, Arlington, USA

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.
High-brightness XFEL is demanding for many users, in particular for certain types of imaging applications. Seeded FELs including self-seeding XFELs were successfully demonstrated. Alternative approaches by enhancing slippage between the x-ray pulse and the electron bunch were also demonstrated. This class of Slippage-enhanced SASE (SeSASE) schemes can be unique for FEL spectral range between 1.5 keV to 4 keV where neither grating-based soft x-ray self-seeding nor crystal-based hard x-ray self-seeding can easily access. SeSASE can provide high-brightness XFEL for high repetition rate machines not suffering from heat load on the crystal monochromator. We report start-to-end simulation results for LCLS-II project and PAL-XFEL project with study on tolerance. Performance comparison between SaSASE FEL and self-seeding FEL in the overlapping frequency range is also presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2017-TUP058

Export •

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