A 0.1 kW operation of the JAERI superconducting RF linac-based FEL

First and stable laser oscillation has been obtained around a wavelength of 24 mu m using the Japan Atomic Energy Research Institute, Tokai (JAERI) su perconducting RF-linac-based FEL driver and far infrared FEL device. The el ectron beam energy and spread are 15.8 MeV and 0.6%, respectively. The beam current varies between 2 and 4 mA, and the pulse width between 0.1 and 0.9 ms, respectively. The near-concentric optical resonator is 14.4 m long, an d uses gold-coated copper mirrors 120 mm in diameter. The hybrid, planar un dulator has 52 periods, 33 mm in length and K = 0.7. Remote-controlled actu ators precisely adjust the optical axes and distance of the mirrors in orde r to coincide with the electron beam and micro pulse repetition rate, respe ctively, before oscillation. The power has been measured and is scattered f rom 10(7) to 10(8) times higher than that of the spontaneous emission. Duri ng the first successful operation, the highest average FEL power was measur ed to be about a hundred watts. The FWHM of the FEL spectrum is around the Fourier-transform limited value, and less than 0.09 mu m, which corresponds to Delta lambda/lambda = 0.37%. The detuning curve of the cavity is asymme tric, and spans about 15 mu m. (C) 1999 Published by Elsevier Science B.V. All rights reserved.