Sub-mm radiation can be generated by conversion of plasma waves into electromagnetic (EM) radiation at strong Langmuir turbulence (LT) via the two-stream instability induced by a high current relativistic electron beam (REB). A plasmon scattering on plasma density fluctuations produces EM emission at the plasma frequency p (“p process”). Nonlinear plasmon-plasmon merging results in the generation of photons nearby the 2nd harmonic of the plasma frequency 2p (2p process”). For plasma densities 1020-1021 m-3, these frequencies are in the range of sub-mm waves: 180-566 GHz. The power density of sub-mm-wave emission from plasmas in the multi-mirror trap GOL-3 (BINP) during injection of a 10-s-REB at plasma densities ne [approximately equal] (1-5)1020 m-3, electron temperatures Te [approximately equal] 1-3 keV and magnetic field B [approximately equal] 4 T was measured to be up to 1 kW/cm3 in the frequency band above 100 GHz.

To calculate the second harmonic emission power from turbulent magnetized plasma we use the model of coalescence of two upper-hybrid waves. Results of these calculations and measured power are in good coincidence in the investigated area of plasma density.