FELs and optical klystrons based on tandem electrostatic accelerators - a tunable coherent source in the 10-1000 micrometer region

Summary form only given. The authors discuss the potential of FELs (free-electron lasers) and microwiggler optical klystrons based on tandem accelerators as a coherent tunable quasi-CW (continuous wave) source in the 10-1000 micrometer region. They demonstrate the feasibility of the concept based on a recently developed 1-A 5-6-MeV tandem accelerator. To extend the operating region of electrostatic accelerators in the mid- to near-IR region, the authors propose the following: (1) Use of the straight geometry tandem electrostatic accelerator operating in the depressed collector mode with a positively charged internal high voltage terminal. The wiggler is placed in the internal terminal, and the electron gun and multistage collector are grounded. This results in an electron beam with high current, high quality, and long pulse duration. (2) Use of microwiggler with λ_w < 5 μ. (3) Use of an optical klystron configuration in which the central part of the wiggler is replaced by a dispersive magnet section to enhance the electron bunching. This makes it possible to obtain substantial gain even with a short microwiggler.