FEL2019 - List of Authors (Li, Y.S.)

Paper	Title	Page
TUP037	Optimization of the Transverse Gradient Undulator (TGU) for Application in a Storage Ring Based XFELO	131
	Y.S. Li University of Chicago, Chicago, Illinois, USA K. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: U.S. Dept. of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357 The stringent energy spread requirement of the XFELO poses a challenge for its application in storage rings. One way to overcome this is by using a transverse gradient undulator (TGU) [1]. The TGU gain formula was discussed previously [2]. In this paper, we begin by reviewing the analytical 3D gain formula derived from the gain convolution formula. Following that, we apply numerical optimization to investigate the optimal beam and field parameters for maximal TGU gain. We found that a small emittance ratio (i.e. "flat beam" configuration) has a strong positive impact on TGU gain, as well as other patterns in the optimal parameters. [1] T. I. Smith et al., J. Appl. Phys. 50 (1979) 4580 [2] R. R. Lindberg et al., in Proceedings FEL’13, New York, USA, 2013, pp. 740-748, paper THOBNO02
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP037
About •	paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019
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TUP038	Axial Symmetry in Spontaneous Undulator Radiation for XFELO Two-Bunch Experiment	134
	Y.S. Li University of Chicago, Chicago, Illinois, USA K. Kim, R.R. Lindberg ANL, Lemont, Illinois, USA
	Funding: U.S. DOE, Office of Science, Office of BES, under Contract No. DE-AC02-06CH11357 and National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams. A well known discrepancy exists between 2D and 3D FEL simulation codes with respect to the radiation field intensity prior to the exponential gain regime [1]. This can be qualitatively explained by the fact that the 3D field representation preserves many more modes than does the axisymmetric field solved for by a 2D code. In this paper, we seek to develop an analytical model that quantifies this difference. We begin by expanding the spontaneous undulator radiation field as a multipole series, whose lowest order mode is axisymmetric. This allows us to calculate the difference in predicted intensity. Next, we confirm these results with numerical calculation and existing FEL codes GINGER and GENESIS. Finally, we discuss the implications of this study with respect to the XFELO two-bunch experiment to be conducted at LCLS-II. [1] Z. Huang and K.-J. Kim, "Review of X-ray free-electron laser theory", Phys. Rev. ST-AB, vol. 10, p. 034801, 2007.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP038
About •	paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Optimization of the Transverse Gradient Undulator (TGU) for Application in a Storage Ring Based XFELO

131

Y.S. Li
University of Chicago, Chicago, Illinois, USA
K. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: U.S. Dept. of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357
The stringent energy spread requirement of the XFELO poses a challenge for its application in storage rings. One way to overcome this is by using a transverse gradient undulator (TGU) [1]. The TGU gain formula was discussed previously [2]. In this paper, we begin by reviewing the analytical 3D gain formula derived from the gain convolution formula. Following that, we apply numerical optimization to investigate the optimal beam and field parameters for maximal TGU gain. We found that a small emittance ratio (i.e. "flat beam" configuration) has a strong positive impact on TGU gain, as well as other patterns in the optimal parameters.
[1] T. I. Smith et al., J. Appl. Phys. 50 (1979) 4580
[2] R. R. Lindberg et al., in Proceedings FEL’13, New York, USA, 2013, pp. 740-748, paper THOBNO02

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP037

About •

paper received ※ 19 August 2019 paper accepted ※ 27 August 2019 issue date ※ 05 November 2019

Export •

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

TUP038

Axial Symmetry in Spontaneous Undulator Radiation for XFELO Two-Bunch Experiment

134

Y.S. Li
University of Chicago, Chicago, Illinois, USA
K. Kim, R.R. Lindberg
ANL, Lemont, Illinois, USA

Funding: U.S. DOE, Office of Science, Office of BES, under Contract No. DE-AC02-06CH11357 and National Science Foundation under Award No. PHY-1549132, the Center for Bright Beams.
A well known discrepancy exists between 2D and 3D FEL simulation codes with respect to the radiation field intensity prior to the exponential gain regime [1]. This can be qualitatively explained by the fact that the 3D field representation preserves many more modes than does the axisymmetric field solved for by a 2D code. In this paper, we seek to develop an analytical model that quantifies this difference. We begin by expanding the spontaneous undulator radiation field as a multipole series, whose lowest order mode is axisymmetric. This allows us to calculate the difference in predicted intensity. Next, we confirm these results with numerical calculation and existing FEL codes GINGER and GENESIS. Finally, we discuss the implications of this study with respect to the XFELO two-bunch experiment to be conducted at LCLS-II.
[1] Z. Huang and K.-J. Kim, "Review of X-ray free-electron laser theory", Phys. Rev. ST-AB, vol. 10, p. 034801, 2007.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-FEL2019-TUP038

About •

paper received ※ 19 August 2019 paper accepted ※ 28 August 2019 issue date ※ 05 November 2019

Export •

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