  Generation of terahertz electromagnetic radiation due to coalescence of
upper-hybrid waves in the long-wavelength region of strong plasma turbulence
driven by a high-current relativistic electron beam in a magnetized plasma is
investigated. The width of frequency spectrum as well as angular
characteristics of this radiation for various values of plasma density and
turbulence energy are calculated using the simple theoretical model adequately
describing beam-plasma experiments at mirror traps. It is shown that the power
density of electromagnetic emission at the second harmonic of plasma frequency
in the terahertz range for these laboratory experiments can reach the level of
1 ${MW/cm}^3$ with 1% conversion efficiency of beam energy losses to
electromagnetic emission.
