a Study of Beam Driven Electrostatic Ion Cyclotron Instabilities in the Ionosphere.
The purpose of this work was to develop an extremely general electrostatic dispersion relation for a collisionless plasma and to code it for a computer. Once this was completed, computer code for the plasma dispersion function was generated, since it too formed an integral part of the work. Since the completed code was bulky, it was used to generate previously published results several times to ensure confidence in its accuracy. When these were successfully demonstrated, several current problems in plasma physics were analyzed. A mechanism was suggested for the excitation of electrostatic ion cyclotron waves at frequencies below the ion cyclotron frequency in the midst of the auroral acceleration region, which is assumed to consist of downward moving double layers. The mechanism involves upward flowing ions interacting with a downward flowing background plasma. Another situation studied was waves at frequencies below the lower hybrid frequency being triggered by a highly energetic low density electron beam in a multi-species plasma. The excited waves are either ion cyclotron resonance cone waves or beam plasma waves. Both waves show stop bands near the gyrofrequencies of the constituent ions. The code was also used to analyze electrostatic ion cyclotron waves with nearly zero frequency in an ion beam plasma. It is shown that the streaming background electrons, in addition to the target (stationary in the chosen frame of reference) ions, make an important contribution to the growth rate of the electrostatic ion cyclotron waves in the zero frequency band. The last case studied was counterstreaming bulk ion drift against neutralizing stationary background electrons. It is shown that electrons much hotter than either ion cause ion acoustic modes to become more unstable than ion cyclotron modes. Disparate masses also destabilize the plasma.
- Pub Date:
- Physics: Fluid and Plasma