Properties of sub-THz waves generated by the plasma during interaction with relativistic electron beam

In the paper, last experiment’s results on sub-THz wave emission from the area of relativistic electron beam-plasma interaction in the GOL-PET device are described. A plasma column with the diameter of 6 cm, length of 2.5 m and electron density (0.2-2)×1015 cm−3 is confined by multiple-mirror magnetic field with mean value of 4 T. The relativistic electron beam injected into the column, has the following parameters: energy Eb ∼ 0.8 MeV, current Ib ∼ 30 kA, current density Jb ∼ 2 kA/cm2 in the mean magnetic field. Previous studies have shown that the beam pumps the plasma electron oscillations in a vicinity of the upper hybrid wave branch. These plasma oscillations can be converted in electromagnetic waves on regular or artificial plasma density gradients in a vicinity of upper hybrid frequency. The electromagnetic waves with the double upper hybrid frequency are also generated in the beam-plasma system due to coalescence of the plasma oscillations in case of high level of the oscillation energy density. The described experiments are devoted to measure the spectral properties of the generated radiation and the direction of the sub-THz plasma emission in depending on plasma and beam parameters. As results the wave emission with the specific power concentrated in the direction along the axis of the plasma column, in the frequency interval 0.25-0.5 THz has been obtained at the plasma density about of 1015 cm−3.