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MOC01 |
Using Pipe With Corrugated Walls for a Sub-Terahertz FEL |
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- G. Stupakov
SLAC, Menlo Park, California, USA
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Funding: This work was supported by Department of Energy contract DE-AC03-76SF00515.
A metallic pipe with corrugated walls supports propagation of a high-frequency mode that is in resonance with a relativistic beam propagating along the axis of the pipe. This mode can be excited by a beam whose length is a fraction of the wavelength. In this work, we discuss another option of excitation of the resonant mode'via the mechanism of the free electron laser instability. This mechanism works if the bunch length is much longer than the wavelength of the radiation, and hence does not require bunch compression. It provides an alternative to excitation by short bunches that can be realized with relatively low energy and low peak-current electron beams.
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Slides MOC01 [1.252 MB]
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| MOC02 |
Optimization of a High Efficiency Free Electron Laser Amplifier |
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- E. Schneidmiller, M.V. Yurkov
DESY, Hamburg, Germany
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Technique of undulator tapering in the post-saturation regime is used at the existing X-ray FELs for increasing the radiation power. We present comprehensive analysis of the problem in the framework of one-dimensional and three-dimensional theory. We find that diffraction effects essentially influence on the choice of the tapering strategy. Our studies resulted in a general law of the undulator tapering for a seeded FEL amplifier as well as for SASE FEL.
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Slides MOC02 [24.462 MB]
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| MOC03 |
Estimate of Free-Electron Laser Gain Length in the Presence of Electron Beam Collective Effects |
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- S. Di Mitri
Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
- S. Spampinati
Cockcroft Institute, Warrington, Cheshire, United Kingdom
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A novel definition for the three-dimensional free electron laser gain length is proposed*, which takes into account the increase of electron beam projected emittance as due, for example, to geometric transverse wakefield and coherent synchrotron radiation developing in linear accelerators. The analysis shows that the gain length is affected by an increase of the electron beam projected emittance, even though the slice (local) emittance is preserved, and found to be in agreement with Genesis code simulation results. It is then shown that the minimum gain length and the maximum of output power may notably differ from the ones derived when collective effects are neglected. The proposed model turns out to be handy for a parametric study of electron beam six-dimensional brightness and FEL performance as function, e.g., of bunch length compression factor, accelerator alignment tolerances and optics design.
* S. Di Mitri, S. Spampinati, Phys. Rev. Special Topics Accel. Beams, 17, 110702 (2014)
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Slides MOC03 [2.528 MB]
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| MOC04 |
Operating of SXFEL in a Single Stage High Gain Harmonic Generation Scheme |
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- G.L. Wang, D.X. Dai, G.R. Wu, X.M. Yang, W.Q. Zhang
DICP, Dalian, People's Republic of China
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The beam energy spread at the entrance of undulator system is of paramount importance for efficient density modulation in high-gain seeded free-electron lasers (FELs). In this paper, the dependencies of high harmonic bunching efficiency in the high-gain harmonic generation (HGHG) schemes on the electron energy spread distribution are studied. Theoretical investigations and multi-dimensional numerical simulations are applied to the cases of uniform and saddle beam energy distributions and compared to a traditional Gaussian distribution. It shows that the uniform and saddle electron energy distributions significantly enhance the performance of HGHG-FELs. A numerical example demonstrates that, with the saddle distribution of sliced beam energy spread controlled by a laser heater, the 30th harmonic radiation can be directly generated by a single-stage seeding scheme for a soft x-ray FEL facility.
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Slides MOC04 [3.345 MB]
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