Parameter analysis for a high-gain harmonic generation FEL using a recently developed 3D polychromatic code

One possible design for a fourth-generation light source is the high-gain h armonic generation (HGHG) free-electron laser (FEL). Here, a coherent seed with a wavelength at a subharmonic of the desired output radiation interact s with the electron beam in an energy-modulating section. This energy modul ation is then converted into spatial bunching while traversing a dispersive section (a three-dipole chicane). The final step is passage through an und ulator tuned to the desired higher harmonic output wavelength. The coherent seed serves to suppress noise and can be at a much lower subharmonic of th e output radiation. Recently, a 3D code that includes multiple frequencies, multiple undulators (both in quantity and/or type), quadrupole magnets, an d dipole magnets was developed to easily simulate HGHG. Here, a brief revie w of the HGHG theory, the code development, the Accelerator Test Facility's (ATF) HGHG FEL experimental parameters, and the parameter analysis from si mulations of this specific experiment will be discussed. (C) 2000 Elsevier Science B.V. All rights reserved.