Generation of High-Power Sub-THz Waves in Magnetized Turbulent Electron Beam Plasmas

Abstract

Sub-THz radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation in a plasma with strong Langmuir (LT) turbulence produced via a two-stream instability of a high current relativistic electron beam (REB). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2^nd harmonic of the plasma frequency 2ω _p (“2ω _p -process”). For plasma densities of 10¹⁴ − 10¹⁵ cm⁻³, these frequencies are in the range of sub-THz waves at 370–570 GHz. The specific power density of sub-THz-wave emission from plasmas in the multi-mirror magnetic trap GOL-3 (at BINP) during injection of a 10-μs-REB with a current density of about 1 kA/cm² at plasma densities n _e  ≈ 5∙10¹⁴ cm⁻³, electron temperatures T _e  ≈ 1.5 keV and magnetic induction B ≈ 4 T was measured to be approx. 1 kW/cm³ in the frequency band around 300 GHz. In the case of a weakly relativistic 100-μs-electron beam (90 keV) with 250 A/cm² the corresponding results are 700 W/cm³ around 90 GHz with an efficiency of 1–2 % at n _e  ≈ 3∙10¹³ cm⁻³ (total power ≈ 30 kW). Theoretical investigations show that at a density of n _e  ≈ 3∙10¹⁵ cm⁻³ and a turbulence level of 5 % the generated sub-THz power can reach ≈ 1 MW/cm³.