THz-range cyclotron super-radiance from photoinjector-formed dense bunch of rotating electrons

Abstract

We study the possibility of terahertz pulse generation based on cyclotron super-radiance (SR) of an extended (in the scale of the wavelength) bunch of rotating electrons, which moves in a cylindrical waveguide with a translational velocity close to the wave's group velocity. In the rest frame, this group synchronism regime corresponds to radiation of an unmoving bunch of excited cyclotron oscillators at a quasi-cutoff frequency of a waveguide mode. We develop the generalized self-consistent model of cyclotron SR in the group synchronism regime describing both the azimuthal self-bunching of rotating electrons and their longitudinal displacements under the action of Coulomb repulsive forces and recoil effects caused by high-frequency magnetic fields of the generated SR pulse. Within the framework of the developed analytical model and based on direct PIC simulations, we demonstrate the feasibility of generating picosecond SR pulses with a central frequency of 1 THz and a peak power of 90 MW by photoinjector-formed electron bunches guided in a strong magnetic field of 10.5 T. Simulations show that in the group synchronism regime, the SR pulse is less affected by longitudinal forces, as compared to the case of mismatched velocities. In addition, the Lorentz force can provide partial self-compression of the electron bunch with the formation of electron density filaments.