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- H.-L. Chang, C. H. Chen, W. C. Cheng, A.-C. Chiang, Y.-C. Huang
NTHU, Hsinchu
- W. K. Lau, G.-H. Luo
NSRRC, Hsinchu
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SASE FEL built up from shot noises exhibits noisy temporal and spectral structures at the output. We propose to use a laser to modulate the electron density at low beam energy and improve the emission characteristics of the SASE FEL at high beam energy. In this scheme, a laser beat wave is incident on the photocathode of an electron gun to generate periodically bunched electrons at the beat-wave frequency. The density modulated electrons can generate superradiance at the harmonics of the beat frequency in all types of single-pass FEL, including Smith-Purcell FEL, Cherenkov FEL, and undulator FEL. The bunching frequency can be further increased by a factor of 10-100 by compressing a chirped, density-modulated, low-energy electron pulse in an alpha magnet, which is subsequently accelerated to high energy for SASE FEL. Computer simulation using particle-in-cell codes, including ASTRA, ELEGANT, and GINGER, shows significant improvements on the gain and coherence of SASE FEL. We will report our detailed study and experimental progress in the conference.
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