Theory and design studies for an rf-linac-driven free-electron laser for the extreme UV

The theoretical design of a free-electron laser (FEL) oscillator configuration operating in the extreme UV spectral region (1000-100 A) is described. The FEL is assumed to be driven by an electron beam from an rf linear accelerator. Since the small signal gain decreases with optical wavelength, and high gains (≅4) are required due to lower mirror reflectivity, the major emphasis on the authors' design studies is to determine the electron-beam quality necessary to operation. The measure of electron-beam quality are values for the current, the transverse emittance, and energy spread. Initial simulation results indicate that an electron beam with the following parameters is required: I ≤ 100A; ε/sub n/ (normalized emittance) ≥ 20π; and Δγ/γ ≥ 0.25%. The present FEL experiment at Los Alamos has exceeded the required current with ≅3-4 times larger values for the normalized emittance and energy spread. Improvements in the emittance and energy spread are expected with development of the photocathode injector