Magnetron driven classical microtron as an injector for a wide band tunable compact far infrared free electron laser

A compact 12 turn classical microtron driven by a 2.8 GHz magnetron has been improved for use as an injector of a compact wide-band far infrared (FIR) free electron laser (FEL). The microtron provides an accelerated beam current of up to 70 mA by total energy of up to 7.2 MeV in a 5.5 μs duration macro pulse. The frequency of the magnetron was stabilized in the range of (3-4)×10^-5 by the frequency pulling of the magnetron with the reflected wave from the accelerating cavity. The measured energy spread and emittances in vertical and horizontal components of the electron beam were less than 0.4%, 1.5 mm·mrad and 3.5 mm·mrad, respectively. A measured temporal deviation of the bunch repetition rate of less than 120 kHz could be obtained by optimization of the microtron operating conditions for the FEL. With a total energy of electrons and macro pulse current of 7 MeV and 45 mA respectively stable FIR lasing could be obtained in the wavelength range from 97 to 150 μm by changing the undulator K-parameter. The accelerating cavity moving system was upgraded to increase the variable range of the electron beam energy from 4.3 to 7 MeV, which provides wide tuning range of the FIR FEL wavelength up to 300 μm