Emission of submm-radiation by strong turbulent plasma at two-stream instability of high current REB

ONE of possible ways to generate submillimeter wave and THz radiation is to use transformation of plasma waves into electromagnetic radiation at strong Langmuir turbulence. We had already described some implementation of such method at the GOL-3 experiments, wherein the mechanism of plasma heating was recognized as the excitation of strong Langmuir turbulence (LT) via a two-stream instability induced by the propagating high current beam. The detailed theoretical consideration of LT-induced electromagnetic emission from turbulent plasmas distinguishes two main processes responsible for electromagnetic radiation emission during the beam-plasma interaction at GOL-3. First, plasmon scattering on plasma density fluctuations yields electromagnetic emission at the plasma frequency ω_p ("ω_p- process"). Second, plasmon-plasmon merging results in production of photons in the vicinity of the double plasma frequency 2ω_p ("2ω_p-process"). For plasma densities of 10¹⁴-10¹⁵ cm^-3, corresponding output radiation frequencies are located in the range from mm to sub-mm waves, ω_p/2π ≅ 90-283GHz, 2ω_p/2π ≅ 180-566GHz. In this paper, we present studies of LT-induced submm-wave emission from GOL-3 plasmas during injection of a 10-μs- REB. We intentionally focused on investigating 2ω_p-emission from the plasma at plasma density n ≈ 10₁₄-10₁₅ cm^-3, and magnetic field strength of 4T.