  The amplification of a surface electromagnetic wave by means of
ultrarelativistic monoenergetic electron bunch running over the flat plasma
surface in absence of a magnetic field is studied theoretically. It is shown
that when the ratio of electron bunch number density to plasma electron number
density multiplied by a powered to 5 relativity factor is much higher than 1,
i.e $\gamma^5 n_b/n_p>> 1$, the saturation field of the surface electromagnetic
wave induced by trapping of bunch electrons gains the magnitude:
$E_x=B_y\approx 0.16 \frac{\omega_p m c}{e} (\frac{2n_b}{\gamma^2 n_p})^{1/7}$
and does not approache the surface electromagnetic wave front breakdown
threshold in plasma. The surface electromagnetic wave saturation energy density
in plasma can exceed the electron bunch energy density. Here, we discuss the
possibility of generation of superpower Teraherz radiation on a basis of such
scheme.
