VLF EMISSION PRODUCED BY A RAREFIED ELECTRON-BEAM DURING ACTIVE EXPERIMENTS IN THE EARTH-IONOSPHERE - CONDITIONS OF OBSERVATION OF THE EMISSION

The peculiarities of whistler waves spontaneously radiated by an elect ron beam artificially injected into the Earth ionosphere are discussed . The conditions of registration of the whistler wave packets by a rem ote on board VLF receiver have been analyzed- they depend on mutual di sposition of the electron gun and the VLF receiver as well as on the p itch angle of the injected electrons. It is shown that the internal fr equency width of the whistler signal, connected with ray representatio n of a wave field, depends oxi the distance between the emitting regio n of the beam and the receiver and determines the lowest bandwidth of the VLF receiver in use. In the case of a dense plasma (when the plasm a frequency omega(p) is much greater than the electron gyrofrequency o mega(c)) the main results are obtained analytically. The effective val ue of the electron collision frequency for the background plasma can b e estimated through measurements of the maximum value of the injection pitch angle of the beam's electrons, which leads to a steep drop in t he level of the whistler signal. It is shown that double-pole. singula rity in the single electron Cherenkov energy loss near the Gendrin's v elocity appears only at a single frequency depending on the beam and t he background plasma parameters. Thus the total growth of the energy l oss in this case reveals an increase by a factor of the order of omega (p)/omega(c) compared to the usual single-pole contribution. The Chere nkov radiation from the sharp leading front of the beam does not revea l any Mach cone structure. The peculiarities of the spectral parameter s of the whistler emission at the Doppler-shifted resonances are also discussed; the Mach cone exists in these cases. Thus this feature can be responsible for the crucial difference between the registration pat tern of high-frequency and whistler frequency emission in active exper iments similar to ARAKS.