FEL2015 - List of Authors (Nause, A.)

Paper	Title	Page
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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TUP008	High-Gain FEL in the Space-Charge Dominated Raman Limit	347
	I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig UCLA, Los Angeles, California, USA
	While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.
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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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Paper

Title

Page

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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TUP008

High-Gain FEL in the Space-Charge Dominated Raman Limit

347

I.I. Gadjev, C. Emma, A. Nause, J.B. Rosenzweig
UCLA, Los Angeles, California, USA

While FEL technology has reached the EUV and X-ray regime at existing machines such as LCLS and SACLA, the scale of these projects is often impractical for research and industrial applications. Sub-millimeter period undulators can reduce the size of a high-gain EUV FEL, but will impose stringent conditions on the electron beam. In particular, a high-gain EUV FEL based on undulators with a sub-millimeter period will require electron beam currents upwards of 1 kA at energies below 100 MeV. Coupled with the small gap of such undulators and their low undulator strengths, K < 0.1, these beam parameters bring longitudinal space-charge effects to the foreground of the FEL process. When the wavelength of plasma oscillations in the electron beam becomes comparable to the gain-length, the 1D theoretical FEL model transitions from the Compton to the Raman limit. In this work, we investigate the behavior of the FEL's gain-length and efficiency in these two limits. The starting point for the analysis was the one-dimensional FEL theory including space-charge forces. The derived results were compared to numerical results of Genesis 1.3 simulations. This theoretical model predicts that in the Raman limit, the gain-length scales as the beam current to the -1/4th power while the efficiency plateaus to a constant.

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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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