IPAC2015 - List of Authors (Wu, J.)

Paper	Title	Page
MOPWI022	Experimental Study of a Two-Color Storage Ring FEL	1198
	J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu FEL/Duke University, Durham, North Carolina, USA S. Huang PKU, Beijing, People's Republic of China J.Y. Li USTC/NSRL, Hefei, Anhui, People's Republic of China N. Vinokurov BINP SB RAS, Novosibirsk, Russia J. Wu SLAC, Menlo Park, California, USA
	Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033. Multi-color Free-electron Lasers (FELs) have been developed on linac based FELs over the past two decades. On the storage ring, the optical klystron (OK) FEL in its early days was demonstrated to produce lasing at two adjacent wavelengths with their spectral separation limited by the bandwidth of single wiggler radiation. Here, we report a systematic experimental study on the two-color operation at the Duke FEL facility, the first experimental demonstration of a tunable two-color harmonic FEL operation of a storage ring based FEL. We demonstrate a simultaneous generation of two FEL wavelengths, one in infrared (IR) and the other in ultraviolet (UV) with a harmonic relationship. The experimental results show a good performance of the two-color FEL operation in terms of two-color wavelength tunability, power tunability and power stability.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWI022
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TUPJE052	Bunch Compression in the Driver Linac for the Proposed NSRRC VUV FEL	1738
	N.Y. Huang, W.K. Lau, A.P. Lee NSRRC, Hsinchu, Taiwan A. Chao, K. Fang, M.-H. Wang, J. Wu SLAC, Menlo Park, California, USA
	A bunch compressor is designed for the S-band driver linac system of the proposed NSRRC VUV free electron laser (FEL). Instead of using a more conventional rf harmonic linearizer, one main feature of this compressor is to use electron linearization optics to correct the nonlinearity in the energy-time correlation of the electron bunch longitudinal phase space. The strategy of compressor design will be discussed by an analytical calculation and particle tracking simulation. The beam dynamics which include the collective instabilities such as the space charge effects, the wake fields and the coherent synchrotron radiation (CSR) effects are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE052
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TUPMA021	Optimization of an Improved SASE (iSASE) FEL	1881
	L. Gupta Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA K. Fang, J. Wu SLAC, Menlo Park, California, USA
	Funding: Supported by US DOE FWP-2013-SLAC-100164 and DOE SULI. In order to improve free electron laser technology for the future LCLSII at SLAC, a new strategy for creating radiation with increased temporal coherence is under development. The improved Self-Amplified Spontaneous Emission (iSASE) FEL utilizes phase shifters which allow for the spontaneously emitted radiation to interact with and stimulate more electrons to radiate coherently. Five phase shifters were simulated, with 34 normal-conducting undulators and focusing-defocusing quadrupoles as an LCLSII FEL lattice using the FEL software Genesis 1.3. Two general schemes, one providing a total phase shift of arbitrary distribution, the other providing a sequential or distributed phase shift, were simulated and optimized using a simulated annealing algorithm. The results suggest that the phase shifters must provide a total shift comparable to the bunch length, and the shifts must be distributed with one large shift, followed by smaller shifts. * J. Wu, A. Marinelli, C. Pellegrini, Proc. FEL2012, pp. 237, Japan (2012). ** J. Wu, et al., Proc. IPAC2013, pp. 2068, China (2013).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA021
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TUPMA030	Narrowband Continuously Tunable Radiation in the 5 to 10 Terahertz Range by Inverse Compton Scattering	1901
	Z. Wu, K. Fang, M.-H. Wang, J. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by U.S. Department of Energy under Grants DE-AC02-76SF00515, DE-FG02-13ER41970 and by DARPA Grant N66001-11-1-4199. 5 to 10 THz has recently become the frontier of THz radiation sources development, pushed by the growing interests of spectroscopy and pump-probe material study in this frequency range. This spectrum “Gap” lies in between the several THz range covered by Electro-Optical crystal based THz generation, and the tens of THz range covered by the difference frequency generation method. The state-of-the-art EO crystal THz source using tilted pulse front technique has been able to reach ~ 100 MV/m peak field strength, large enough to be used in an inverse Compton scattering process to push these low energy photons to shorter wavelengths of the desired 5-10 THz range. The required electron beam energy is within 1~2 MeV, therefore a compact footprint of the whole system. The process would occur coherently granted the electron beam is bunched to a fraction of the radiation wavelengths (several microns). A system operating at KHz or even MHz repetition rate is possible given the low electron energy and thus low RF acceleration gradient required. This work will explore the scheme with design parameters and simulation results.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA030
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TUPMA031	Dispersive Property of the Pulse Front Tilt of a Short Pulse Optical Undulator	1904
	M.-H. Wang, J. Wu, Z. Wu SLAC, Menlo Park, California, USA
	Funding: Work supported by the US DOE No. DE-AC02-76SF00515. A short pulse laser can be used as an optical undulator to achieve a high-gain and high-brightness X-ray free electron laser (FEL) [1]. To extend the interaction duration of electron and laser field, the electron and the laser will propagate toward each other with an small angle. In addition, to maintain the FEL lasing resonant condition, the laser pulse shape need be flattened and the pulse front will be titled. Due to the short pulse duration, the laser pulse has a broad bandwidth. In this paper, we will first describe the method of generalized Gaussian beam propagation using ray matrix. By applying the Gaussian beam ray matrix, we can study the dispersive property after the pulse front of the short laser is tilted. The results of the optics design for the proposal of SLAC Compton scattering FEL are shown as an example in this paper. [1] C. Chang, et al.,“High-brightness X-ray free-electron laser with an optical undulator by pulse shaping”. Optics Express, Vol. 21, Issue 26, pp. 32013-32018 (2013).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA031
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Paper

Title

Page

Experimental Study of a Two-Color Storage Ring FEL

1198

J. Yan, H. Hao, S.F. Mikhailov, V. Popov, Y.K. Wu
FEL/Duke University, Durham, North Carolina, USA
S. Huang
PKU, Beijing, People's Republic of China
J.Y. Li
USTC/NSRL, Hefei, Anhui, People's Republic of China
N. Vinokurov
BINP SB RAS, Novosibirsk, Russia
J. Wu
SLAC, Menlo Park, California, USA

Funding: This work is supported in part by the US DOE grant no. DE-FG02-97ER41033.
Multi-color Free-electron Lasers (FELs) have been developed on linac based FELs over the past two decades. On the storage ring, the optical klystron (OK) FEL in its early days was demonstrated to produce lasing at two adjacent wavelengths with their spectral separation limited by the bandwidth of single wiggler radiation. Here, we report a systematic experimental study on the two-color operation at the Duke FEL facility, the first experimental demonstration of a tunable two-color harmonic FEL operation of a storage ring based FEL. We demonstrate a simultaneous generation of two FEL wavelengths, one in infrared (IR) and the other in ultraviolet (UV) with a harmonic relationship. The experimental results show a good performance of the two-color FEL operation in terms of two-color wavelength tunability, power tunability and power stability.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOPWI022

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

TUPJE052

Bunch Compression in the Driver Linac for the Proposed NSRRC VUV FEL

1738

N.Y. Huang, W.K. Lau, A.P. Lee
NSRRC, Hsinchu, Taiwan
A. Chao, K. Fang, M.-H. Wang, J. Wu
SLAC, Menlo Park, California, USA

A bunch compressor is designed for the S-band driver linac system of the proposed NSRRC VUV free electron laser (FEL). Instead of using a more conventional rf harmonic linearizer, one main feature of this compressor is to use electron linearization optics to correct the nonlinearity in the energy-time correlation of the electron bunch longitudinal phase space. The strategy of compressor design will be discussed by an analytical calculation and particle tracking simulation. The beam dynamics which include the collective instabilities such as the space charge effects, the wake fields and the coherent synchrotron radiation (CSR) effects are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPJE052

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TUPMA021

Optimization of an Improved SASE (iSASE) FEL

1881

L. Gupta
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
K. Fang, J. Wu
SLAC, Menlo Park, California, USA

Funding: Supported by US DOE FWP-2013-SLAC-100164 and DOE SULI.
In order to improve free electron laser technology for the future LCLSII at SLAC, a new strategy for creating radiation with increased temporal coherence is under development. The improved Self-Amplified Spontaneous Emission (iSASE) FEL utilizes phase shifters which allow for the spontaneously emitted radiation to interact with and stimulate more electrons to radiate coherently. Five phase shifters were simulated, with 34 normal-conducting undulators and focusing-defocusing quadrupoles as an LCLSII FEL lattice using the FEL software Genesis 1.3. Two general schemes, one providing a total phase shift of arbitrary distribution, the other providing a sequential or distributed phase shift, were simulated and optimized using a simulated annealing algorithm. The results suggest that the phase shifters must provide a total shift comparable to the bunch length, and the shifts must be distributed with one large shift, followed by smaller shifts.
* J. Wu, A. Marinelli, C. Pellegrini, Proc. FEL2012, pp. 237, Japan (2012).
** J. Wu, et al., Proc. IPAC2013, pp. 2068, China (2013).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA021

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TUPMA030

Narrowband Continuously Tunable Radiation in the 5 to 10 Terahertz Range by Inverse Compton Scattering

1901

Z. Wu, K. Fang, M.-H. Wang, J. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by U.S. Department of Energy under Grants DE-AC02-76SF00515, DE-FG02-13ER41970 and by DARPA Grant N66001-11-1-4199.
5 to 10 THz has recently become the frontier of THz radiation sources development, pushed by the growing interests of spectroscopy and pump-probe material study in this frequency range. This spectrum “Gap” lies in between the several THz range covered by Electro-Optical crystal based THz generation, and the tens of THz range covered by the difference frequency generation method. The state-of-the-art EO crystal THz source using tilted pulse front technique has been able to reach ~ 100 MV/m peak field strength, large enough to be used in an inverse Compton scattering process to push these low energy photons to shorter wavelengths of the desired 5-10 THz range. The required electron beam energy is within 1~2 MeV, therefore a compact footprint of the whole system. The process would occur coherently granted the electron beam is bunched to a fraction of the radiation wavelengths (several microns). A system operating at KHz or even MHz repetition rate is possible given the low electron energy and thus low RF acceleration gradient required. This work will explore the scheme with design parameters and simulation results.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA030

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

TUPMA031

Dispersive Property of the Pulse Front Tilt of a Short Pulse Optical Undulator

1904

M.-H. Wang, J. Wu, Z. Wu
SLAC, Menlo Park, California, USA

Funding: Work supported by the US DOE No. DE-AC02-76SF00515.
A short pulse laser can be used as an optical undulator to achieve a high-gain and high-brightness X-ray free electron laser (FEL) [1]. To extend the interaction duration of electron and laser field, the electron and the laser will propagate toward each other with an small angle. In addition, to maintain the FEL lasing resonant condition, the laser pulse shape need be flattened and the pulse front will be titled. Due to the short pulse duration, the laser pulse has a broad bandwidth. In this paper, we will first describe the method of generalized Gaussian beam propagation using ray matrix. By applying the Gaussian beam ray matrix, we can study the dispersive property after the pulse front of the short laser is tilted. The results of the optics design for the proposal of SLAC Compton scattering FEL are shown as an example in this paper.
[1] C. Chang, et al.,“High-brightness X-ray free-electron laser with an optical undulator by pulse shaping”. Optics Express, Vol. 21, Issue 26, pp. 32013-32018 (2013).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-TUPMA031

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