Efficient generation of -radiation in a beam-driven thick plasma with oblique density modulation

Recent experiments on the collective interaction of gigawatt electron beams with plasma at the GOL-PET facility have shown that the power of the electromagnetic radiation at the plasma frequency increases tens of times if the starting plasma is created with quasiperiodic radial density gradients. One of the mechanisms capable of providing highly efficient conversion of an unstable beam-driven wave into an electromagnetic one in the presence of periodic density perturbations is the mechanism of plasma antenna. However, earlier this mechanism was considered only for strictly longitudinal modulation of the plasma density, when its efficiency dropped drastically if the transverse size of the plasma significantly exceeded the radiation wavelength. In this work, based on both analytical theory and particle-in-cell modelling, we will show that the presence of oblique modulation of the plasma density makes the antenna mechanism effective even in a thick plasma, if the long-wavelength satellite of the most unstable beam-driven wave falls into resonance with natural plasma oscillations.