| Abstract: | We consider effects related to acceleration of electrons by high-frequency plasma turbulence in the ionospheric F-region modified
by powerful radio waves. The threshold of avalanche growth of the number of accelerated particles due to additional ionization
is determined for pump-wave frequencies far from the multiple cyclotron resonance. The steady-state density of the accelerated
electrons is found for the above pump-frequency values taking into account both turbulent trapping in the accelerating layer
due to scattering of plasma waves and the return of electrons to this layer due to collisions. If the pump wave frequency
is close to the multiple cyclotron resonance, fast electron distribution with significant transverse anisotropy is formed.
Relaxation of this distribution due to collisions with charged particles outside the accelerating layer leads to the appearance
of a maximum over transverse velocities in the tail of the distribution function. We propose a generation mechanism for the
broad upshifted maximum feature in the spectrum of stimulated electromagnetic emission, which is related to the cyclotron
instability of the accelerated electrons. The instability occurs in the double-resonance region in which the pump frequency
is close to both the upper-hybrid and multiple-cyclotron frequency.
Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika,
Vol. 42, No. 7, pp. 651–669, July 1999. |
