Powerful multichannel schemes of spatially-extended planar FEMs operated with two-dimensional distributed feedback

Novel schemes of powerful multichannel planar FEMs was developed based on two parallel sheet beams 0.8 MeV / 1 kA forming by the accelerator ELMI. In 75 GHz frequency band two-channel planar FEM operating with two-dimensional distributed feedback was elaborated. For record transverse size of interaction space (up to 45 × 2.5 wavelengths) synchronization of emission from both electron beams and realization of stable narrow-band generation have been demonstrated. As a result, spatially-coherent radiation with the output power of 30-50 MW and pulse duration of ~100 ns was obtained in this FEM in each channel. To advance powerful long-pulse FEM into THz frequency range original project of two-stage oscillator is under development at the ELMI accelerator. As a microwave system for such oscillator a ring cavity based on four Bragg deflectors has been proposed. Recent results of theoretical and experimental studies of this FEM scheme are presented.