| Paper | Title | Page |
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| MOPPH004 | Effect of Energy Spread on Start Current of Smith-Purcell BWO | 13 |
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| We perform a linear analysis of Maxwell-Vlasov equations for Smith-Purcell Backward Wave Oscillator, including the energy spread of the initial beam distribution. The expression for start current as a function of energy spread is obtained and its dependence on energy spread is discussed. The effect of beam emittance is also included through equivalent energy spread. Results of linear analysis are compared with full nonlinear numerical simulations. | ||
| MOPPH013 | Mode Growth and Competition in the X-ray FEL Oscillator Start-up from Noise | 32 |
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| We describe the radiation properties of an X-ray, free electron laser (FEL) oscillator starting with its start-up from noise through saturation. We decompose the initially chaotic undulator radiation into the longitudinal modes of the resonator whose properties are largely determined by the transverse gain profile and the bandwidth of the Bragg mirror. Because the radiation is initially comprised of several modes whose growth rates are comparable, we show that only after many oscillator passes is the output pulse dominantly characterized by the lowest-order, gaussian mode. We also comment on the transverse structure of the radiation, and discuss how the FEL gain can modify the free space resonator modes. Understanding the full longitudinal and transverse structure during the initial amplification will be critical in assessing the tolerances on electron beam, undulator, and optical cavity required for robust operation. | ||
| MOPPH037 | Smith-Purcell BWO with Electron Beam Focussing | 67 |
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We have recently studied the electron beam requirement for successful operation of Smith-Purcell Backward Wave Oscillator and found that one requires a flat electron beam*. Without focussing, the rquirement leads to a very stringent condition on vertical emittance. In this paper, we discuss another way to produce flat beam by focussing the electron beam and show that the method leads to an improved performance of Smith-Purcell FEL.
* K.-J. Kim and V. Kumar, Phys. Rev. ST Accel. Beams 10, 080702 (2007). |