FEL2015 - List of Authors (Hemsing, E.)

Paper	Title	Page
MOB03	Transforming the FEL: Coherence, Complex Structures, and Exotic Beams	10
	E. Hemsing SLAC, Menlo Park, California, USA
	Modern high brightness electron beams used in FELs are extremely versatile and highly malleable. This flexibility can be used to precisely tailor the properties of the FEL light for improved temporal coherence (as in external seeding), but can also be exploited in new ways to generate exotic FEL modes of twisted light that carry orbital angular momentum (OAM) for new science. In this talk, I will describe how lasers and undulator harmonics can be combined to produce both simple and complex e-beam distributions that emit intense, coherent, and highly tunable OAM light in future FELs.
	Slides MOB03 [12.208 MB]
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MOP078	Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam	221
	R. Ianconescu Shenkar College of Engineering and Design, Ramat Gan, Israel A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel E. Hemsing, A. Marinelli SLAC, Menlo Park, California, USA A. Nause UCLA, Los Angeles, USA
	Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF) The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1]. [1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015) [2] E. Allaria et al., Nat. Photonics 7, 913 (2013) [3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)
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TUP027	Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA	422
	B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer SLAC, Menlo Park, California, USA D. Xiang Shanghai Jiao Tong University, Shanghai, People's Republic of China
	The Echo program currently underway at SLAC's NLCTA test accelerator aims to use Echo-Enabled Harmonic Generation (EEHG) to produce considerable bunching in the electron beam at high harmonics of a 2.4um seed laser. The production of such high harmonics in the EUV wavelength range necessitates an efficient radiator and associated light diagnostics to accurately characterize and tune the echo effect. We have installed and commissioned the Visible to Infrared SASE Amplifier (VISA) undulator, a strong focusing two meter long planar undulator of Halbach array design with 1.8cm period length. To characterize the output radiation, we have designed, built, and calibrated a grazing incidence EUV spectrometer which operates between 12-120nm with resolution sufficient to resolve individual harmonics. An absolute wavelength calibration is achieved by using both EEHG and High Gain Harmonic Generation (HGHG) signals from the undulator.
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WEC04	Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise
	D.F. Ratner, E. Hemsing, A. Marinelli SLAC, Menlo Park, California, USA A. Gover University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel A. Nause UCLA, Los Angeles, USA
	The phenomenon of Dicke's subradiance, in which the collective properties of a system suppress radiation, has received broad interest in atomic physics, but can also be applied to relativistic electron beams. The resulting "quiet" beam generates less spontaneous undulator radiation than emitted even by a random shot noise beam. Quiet beams could have diverse accelerator applications, including lowering power requirements for seeded FELs. Here we present recent experimental observations at the Next Linear Collider Test Accelerator and discuss prospects for pushing the phenomenon to X-ray wavelengths.
	Slides WEC04 [2.935 MB]
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WEP025	Effect of Microbunching on Seeding Schemes for LCLS-II	639
	G. Penn, J. Qiang LBNL, Berkeley, California, USA P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang SLAC, Menlo Park, California, USA
	Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.
	Poster WEP025 [0.962 MB]
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Paper

Title

Page

Transforming the FEL: Coherence, Complex Structures, and Exotic Beams

10

E. Hemsing
SLAC, Menlo Park, California, USA

Modern high brightness electron beams used in FELs are extremely versatile and highly malleable. This flexibility can be used to precisely tailor the properties of the FEL light for improved temporal coherence (as in external seeding), but can also be exploited in new ways to generate exotic FEL modes of twisted light that carry orbital angular momentum (OAM) for new science. In this talk, I will describe how lasers and undulator harmonics can be combined to produce both simple and complex e-beam distributions that emit intense, coherent, and highly tunable OAM light in future FELs.

Slides MOB03 [12.208 MB]

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MOP078

Sub-Radiance and Enhanced-Radiance of Undulator Radiation from a Correlated Electron Beam

221

R. Ianconescu
Shenkar College of Engineering and Design, Ramat Gan, Israel
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
E. Hemsing, A. Marinelli
SLAC, Menlo Park, California, USA
A. Nause
UCLA, Los Angeles, USA

Funding: We acknowledge the United States - Israel Binational Science Foundation (BSF)
The radiant intensity of Synchrotron Undulator Radiation (UR) depends on the current noise spectrum of the electron beam injected into the wiggler. The current noise spectrum and intensity can be controlled (suppressed or enhanced relative to the shot-noise level) by the effect of collective longitudinal space charge interaction in a drift and dispersion sections[1]. This new control lever is of significant interest for possible control of SASE in FEL, since UR is the incoherent seed of SASE. Thus, control of spontaneous UR is a way to enhance the coherence of seeded FEL [2], or alternatively, obtain enhanced radiation from a cascade noise-amplified electron beam [3]. The dependence of UR emission on the current noise is primarily a result of the longitudinal correlation of the e-beam distribution due to the longitudinal space charge effect. However, at short wavelengths, 3-D effects of transverse correlation and effects of emittance disrupts the proportionality relation between the UR intensity and e-beam current noise. We present analysis and simulation of UR subradiance/superradiance under various ranges of beam parameters, and compare to recent experimental observations [1].
[1] D. Ratner et al., PRST - ACCELERATORS AND BEAMS 18, 050703 (2015)
[2] E. Allaria et al., Nat. Photonics 7, 913 (2013)
[3] A. Marinelli et al., Phys. Rev. Lett. 110, 264802 (27 June 2013)

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TUP027

Facility Upgrades for the High Harmonic Echo Program at SLAC's NLCTA

422

B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer
SLAC, Menlo Park, California, USA
D. Xiang
Shanghai Jiao Tong University, Shanghai, People's Republic of China

The Echo program currently underway at SLAC's NLCTA test accelerator aims to use Echo-Enabled Harmonic Generation (EEHG) to produce considerable bunching in the electron beam at high harmonics of a 2.4um seed laser. The production of such high harmonics in the EUV wavelength range necessitates an efficient radiator and associated light diagnostics to accurately characterize and tune the echo effect. We have installed and commissioned the Visible to Infrared SASE Amplifier (VISA) undulator, a strong focusing two meter long planar undulator of Halbach array design with 1.8cm period length. To characterize the output radiation, we have designed, built, and calibrated a grazing incidence EUV spectrometer which operates between 12-120nm with resolution sufficient to resolve individual harmonics. An absolute wavelength calibration is achieved by using both EEHG and High Gain Harmonic Generation (HGHG) signals from the undulator.

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WEC04

Subradiant Spontaneous Undulator Emission through Collective Suppression of Shot Noise

D.F. Ratner, E. Hemsing, A. Marinelli
SLAC, Menlo Park, California, USA
A. Gover
University of Tel-Aviv, Faculty of Engineering, Tel-Aviv, Israel
A. Nause
UCLA, Los Angeles, USA

The phenomenon of Dicke's subradiance, in which the collective properties of a system suppress radiation, has received broad interest in atomic physics, but can also be applied to relativistic electron beams. The resulting "quiet" beam generates less spontaneous undulator radiation than emitted even by a random shot noise beam. Quiet beams could have diverse accelerator applications, including lowering power requirements for seeded FELs. Here we present recent experimental observations at the Next Linear Collider Test Accelerator and discuss prospects for pushing the phenomenon to X-ray wavelengths.

Slides WEC04 [2.935 MB]

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WEP025

Effect of Microbunching on Seeding Schemes for LCLS-II

639

G. Penn, J. Qiang
LBNL, Berkeley, California, USA
P. Emma, E. Hemsing, Z. Huang, G. Marcus, T.O. Raubenheimer, L. Wang
SLAC, Menlo Park, California, USA

Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
External seeding and self-seeding schemes are particularly sensitive to distortions and fluctuations in the electron beam profile. Wakefields and the microbunching instability are important sources of such imperfections. Even at modest levels, their influence can degrade the spectrum and decrease the output brightness. These effects are evaluated for seeded FELs at the soft X-ray beam line of LCLS-II. FEL simulations are performed in GENESIS based on various realistic electron distributions obtained using the IMPACT tracking code. The sensitivity depends on both the seeding scheme and the output wavelength.

Poster WEP025 [0.962 MB]

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