THZ-Spectrum of Megawatt Power Flux Generated by REB in a Plasma Column with a Strong Density Drop at the Output End *

Studies on the generation of electromagnetic radiation during beam-plasma interaction are of considerable scientific interest from the standpoint of analyzing the results of astrophysical observations [1] . Such studies look no less important from the standpoint of solving a wide range of practical problems using high-powerful submillimeter radiation. Experimental and theoretical studies on multimegawatt power submillimeter wave generation due to intense interaction of a relativistic electron beam (REB) with a magnetized plasma column are carried out in BINP SB RAS [2] . In the experiments performed at the GOL-PET facility, the beam with parameters 0.5 MeV/15 kA/6 μs was propagated in a magnetized (induction up to 4.7 T) plasma column with the diameter 6 cm, length 2 m and density (1÷2)x10 15 cm -3 . A radiation flux generated due to beam-plasma interaction was extracted in atmosphere through an output fluoroplastic window of 18 cm diameter. We measured the power and the spectral power density of this flux in the frequency band 0.1÷0.8 THz for various plasma density distributions. The radiation angular distribution of the output flux propagated in the hall atmosphere was also measured. The experiments have shown that the maximal spectral power density of the flux power is located in the frequency range 0.2÷0.35 THz that is the area of the upper-hybrid frequency of plasma oscillations. The value of the spectral power density in this frequency interval depends on the plasma density distribution over the plasma column diameter and on the law of density decrease along the axis at the beam output from the column. The experimental results are discussed in comparison with analytical and computer modeling.