V.B. Bobylev

Project of powerful 4-beam planar FEM with distributed feedback for 75 GHz band

Theoretical and numerical considerations have shown that a planar FEM with 2-D distributed feedback is suitable to be used as a module for constructing multichannel devices to produce microwave radiation of GW level. Computer simulations for operation of 4-modules FEM-generator have demonstrated a perfect synchronization of all modules even at a little bit different energies of the electron beams. The project of 4-channel FEM-generator is designed on the base of the “ELMF”-device.

Progress in investigations on microwave FEL driven by microsecond sheet beam

For production of mm-radiation with 10 GW power one needs a few tens of kAs current of 1 MeV electrons passing through a generator. Ribbon or sheet E-beams allow one to reach this value of the current. In the result of our investigations at U-2 accelerator in 1994 this type of the beams with 30 kA current at 10 /spl mu/s duration was generated and transported through the slit vacuum channel. In 1996 at this accelerator in modelling experiments with the beam current 3-5 kA in a passive magnetic undulator of 4 cm period we also obtained 200 J energy of 4 mm radiation in a few /spl mu/s pulse. The next step of investigations was aimed to reach the maximal efficiency of the microwave generation at a single mode operation of the generator. On this goal in 1997-98 we made reconstruction of the experimental setup intended to investigate FEM-oscillator. In order to increase productivity of the investigations this setup was replaced from the U-2 accelerator to the U-3 one that was specially reconstructed for generation of sheet beams.

Generation and transformation of 0.4-mj ribbon beam with a U-2 device

The paper presents the experimental results on generating and transforming the ribbon (3.5 X 130 cm) beam with the electron energy 1 MeV, beam current 70 kA and pulse duration 8 microsecond(s) . The 70% efficiency of the energy transfer from a capacitor storage to the ribbon beam has been achieved. The close value of the efficiency has been obtained for transforming the ribbon beam to the compressed circular one at the optimal conditions. According to the measurements the angular spread of the compressed beam is less than 100.