Generation Of Intense Spatially Coherent Superradiant Pulses In Strongly Oversized 2d Periodical Surface-Wave Structure

We present the results of experiments on generation of high-power superradiant (SR) pulses by an extended electron bunch moving in a cylindrical surface-wave structure with two-dimensional periodical corrugation. In such a structure, azimuthally propagating wave fluxes are excited, which synchronize radiation from different azimuthal segments of a tubular electron bunch with a diameter greatly exceeding the wavelength. This facilitates a drastic increase in total electron current and, correspondingly, in SR pulses peak power while maintaining the azimuthal coherence of the radiation. In experiments carried out, subnanosecond 90GHz SR pulses with a record-level peak power of up to 150MW and an axially symmetric directional pattern were generated. The results of experiments are in line with the theoretical predictions based on the quasi-optical approach and direct particle-in-cell simulations.