Multi-megawatt terahertz emission of a magnetized plasma with strong density gradients under the injection of a kiloampere REB

Injection of a relativistic electron beam (0.8 MeV, 10 kA, 5 \textmu s) into a magnetized plasma column has been actively studied last years at the GOL-PET facility as a method for generating high-power tunable terahertz radiation. Recent experiments [1] have shown that the power of radiation flux along the plasma column at the fundamental plasma frequency harmonic achieves 4 MW in case of strong radial plasma density gradients. We report that creating a low density plasma gap between the plasma column end and a graphite collector for the E-beam allows us to reach the power level of 10 MW in the radiation flux. Theoretical ideas about mechanisms of enhanced THz generation in the beam-plasma system will be also presented. The work was supported in part by the Russian Science Foundation (project no.19-12-00250). [1] Arzhannikov A Vet al. \textit{Plasma Physics and Controlled Fusion }\textbf{62,} 045002 (2020)