Stabilization of the microtron-injector for a wide-band compact FIR FEL

To provide parameters of a simple and inexpensive magnetron-driven microtron-injector acceptable for a wide-band FIR FEL, the microtron has been improved through stabilization of the beam current and the magnetron frequency. The beam current was stabilized during the macro-pulse by increasing the magnetron anode current. The pulse stabilization of the emission current makes possible the microtron operation with the maximal accelerated current, without risk of break-downs in the cavity and keeps the instability of the accelerated current at approximately 1% during long-time experiments. The magnetron frequency was stabilized using the microtron accelerating cavity as a stabilizing external resonator in a simple scheme that involved the cavity loading of the magnetron through a ferrite insulator. The scheme provides stabilization of the magnetron frequency with a coefficient of 3.5. The stabilization of current and the frequency at the microtron FIR FEL-injector provides satisfactory intrapulse stability of the extracted lasing power of 40-50 W in the FIR macro-pulse having duration of 3-4 μs and a long-time pulse-to-pulse instability of the FIR pulse energy in the range of ≤10%. Results of simulations of the stabilization based on the microtron operating parameters and measured results are presented and discussed