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WEOCNO01 |
Simulation Studies of FEL Green Function and Its Saturation |
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- Y.C. Jing, Y. Hao, V. Litvinenko, G. Wang
BNL, Upton, Long Island, New York, USA
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FEL amplifiers can be used for a number of applications ranging from the HGHG [1] , the coherent seed amplifying [2] or amplifier in Coherent electron Cooler [3]. Linear response of an FEL amplifier can be described using its Green function. In this paper we present results of detailed studies of the evolution and saturation of the Green function in FEL as function of its length. We are using time resolved mode of the code Genesis [4] for these studies, which include delta-function like seed and shot noise in electron beam. We simulate a statistically representative set of initial shot noise with and without the seed, and extract the Green function amplitude and phase evolution, as well as their fluctuation. We present results for three spectral ranges: the IR, the visible and the soft X-rays. We summarize our finding and compare them with a simple theoretical formula.
[1] L.H. Yu et al., science, 289 (2000)
[2] J. Feldhaus et al., NIMA, 1997
[3] V. N. Litvinenko et al., Phys. Rev. Lett. 102, 114801 (2009)
[4] S.Reiche, Genesis 2.0
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Slides WEOCNO01 [0.479 MB]
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WEOCNO02 |
Echo-enabled Devices and Coulombian Diffusion |
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- G. Dattoli, E. Sabia
ENEA C.R. Frascati, Frascati (Roma), Italy
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The mechanism of Echo-enabled FEL devices have been discussed by Stupakov and coworkers who have provided detailed analysis for an experimental implementation of their proposal. More recently the effect of the Coulombian diffusion as an element determining a dilution of the bunching coefficients has been studied by Stupakov, the problem has been treated using the diffusion equation coupled to a kind of ray tracing procedure. We propose a different approach based on the use of a Vlasov equation composed by two contributions accounting for the Liouville and diffusive part of the interaction. The equation is solved using simplectic integration procedures which provide an effective method of solution, easily implemented numerically, flexible and modular. The results which can be extended to different experimental conditions are confronted with those of earlier works.
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Slides WEOCNO02 [1.474 MB]
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| WEOCNO03 |
3-D Theory of a High Gain Free-Electron Laser Based on a Transverse Gradient Undulator |
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- P. Baxevanis, Y. Ding, Z. Huang, R.D. Ruth
SLAC, Menlo Park, California, USA
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The performance of a free-electron laser (FEL) depends significantly on the various parameters of the driving electron beam. In particular, a large energy spread in the beam results in a great reduction of the FEL gain, an effect which is relevant when one considers FELs driven by plasma accelerators or storage rings. For such cases, one possible solution is to use a transverse gradient undulator (TGU) [*,**]. In this concept, the energy spread problem is mitigated by properly dispersing the e-beam and introducing a linear, transverse field dependence in the undulator. This paper presents a self-consistent theoretical analysis of a TGU-based high gain FEL, taking into account three-dimensional (3-D) effects and beam size variations along the undulator [***]. The results of our theory compare favorably with simulation and are used in fast optimization studies of various X-ray FEL configurations.
*T. Smith et al., J. Appl. Phys. 50, 4580 (1979).
**Z. Huang, Y. Ding, C. Schroeder, Phys. Rev. Lett. 109, 204801 (2012).
***P. Baxevanis, R. Ruth, Z. Huang, Phys. Rev. ST-AB 16, 010705 (2013).
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Slides WEOCNO03 [3.217 MB]
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WEOCNO04 |
The Echo Scheme: An Efficient Alternative to Slicing on Storage Rings |
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- C. Evain
SOLEIL, Gif-sur-Yvette, France
- C. Evain
PhLAM/CERCLA, Villeneuve d'Ascq Cedex, France
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Echo-enabled harmonic generation was proposed in Free Electron Lasers [1] in order to enhance dramatically the FEL radiation on very high harmonic orders. Two laser-electron interactions that modulate the longitudinal charge distribution at a harmonic number of the laser wavelength are required, before FEL radiation is produced in a last radiator. The scheme has been applied to a storage ring [2], in order to produce femtosecond pulses of soft x-ray coherent undulator radiation. The output photon flux is expected to be several orders of magnitude higher than in the case of the conventional slicing scheme. Analytical as well as numerical simulations are presented in the case of SOLEIL storage ring.
[1] G. Stupakov, PRL 102, 074801 (2009).
[2] C. Evain et al., New Journal of Physics 14, 023003 (2012).
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Slides WEOCNO04 [2.067 MB]
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