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 90 GHz SR pulses with a record-level peak power of up to 150 MW 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.