Excitation of VLF waves by an electron beam injected into the ionosphere

Abstract

We propose a scenario for radiation of electromagnetic whistlers as a result of the injection of a modulated electron beam into the ionosphere. We show that for plasma parameters typical of the ionosphere and electron beam parameters typical of electron guns carried into space aboard rockets or spacecraft, the interaction can result in the instability of electrostatic waves driven by Cherenkov resonance between the waves and the beam. A linear stability analysis was carried out for two limiting cases: a wide and a narrow electron beam; the wave excitation is shown to develop at typical distances of the order of 1 km. Nonlinear evolution of the instability was investigated by a combination of analytical and numerical methods. Electron beam energy is efficiently transformed into the electrostatic mode. The mechanism of electromagnetic mode generation is then dipole radiation from the electron beam, which is strongly bunched as a result of the electrostatic instability. The efficiency of radiation is a strong function of the ratio of the electron beam velocity to electron Alfven velocity (Vae = C O)ce/O)pe); the possibility of increasing the efficiency of radiation is discussed.

Interaction of electromagnetic waves with a radially bounded electron beam

“…where n p is the background plasma density. One can see that the linear growth rate calculated taking into account the narrow beam conditions is proportional to (n b /n p ) 1/2 while in the wide beam case one has γ ∝ (n b /n p ) 1/3 [20].…”

“…The beam can be considered as narrow when the electromagnetic energy leakage in the perpendicular direction exceeds the accumulation rate of energy inside the interaction region. This condition can be written in a draft manner as γr L < v g⊥ [20], where v g⊥ is the perpendicular group velocity of the propagating whistler branch. The simulation code developed by Volokitin and Krafft [25] is applicable in this case and the field components governing the particles' motion can be calculated using Green functions techniques for a given modulated current slowly varying along the ambient magnetic field.…”

Nonlinear dynamics of electron bunches in the presence of dissipative effects

“…Recent results on Cherenkov emission of whistlers produced during the interaction of a modulated electron beam with a magnetized plasma have also been obtained in laboratory experiments (Krafft et al 1994a,b;Kostrov et al 1998). However, only the classical case of the nonlinear interaction of electrostatic waves with a modulated beam, with dissipative effects being neglected, has been given much theoretical consideration (O'Neil et al 1971;Matsiborko et al 1972;Jungwirth and Krlin 1975;Pivavorov et al 1995).…”

Resonant three-wave interaction in the presence of suprathermal electron fluxes

“…O'Neil et al, 1971;Shevchenko, 1968, 1971;Matsiborko et al, 1972Matsiborko et al, , 1973Kovalenko, 1983;Pivovarov et al, 1995;Volokitin and Krafft, 2000, 2001a, 2001b, 2004Krafft et al, 2000;Volokitin, 2002, 2003a): first, the study of the instability and the saturation processes of a single monochromatic wave (which can be used for the modeling of some experimental situations in laboratory), and second, the evolution of a wide spectrum of waves at the stage when the turbulence is well developed. However, the intermediate case, when only a few wave modes are governing the nonlinear processes through their mutual interaction and their interaction with the particles, has also to be considered for the adequate modeling of some space plasma phenomena.…”