Theoretical Investigations of Absolute and Convective Instabilities in BeamPlasma Systems.
Abstract
The Cerenkov interaction of a monoenergetic electron beam with the upper branch plasma wave of a cylindrical, homogeneous, Maxwellian magnetoplasma was investigated in the linear and nonlinear regimes. From linear theory the appropriate dispersion relation was derived and solved numerically to obtain conditions for the existence of the absolute and convective instabilities. The instability is shown to be convective when the group velocity of the plasma wave is positive, and is absolute when the group velocity is negative and the beam density exceeds a threshold density. Expressions for this were derived from a simplified form of the dispersion relation valid in the weak beam limit. A computer simulation was used to study the nonlinear regime. When a single mode dominates the instability, beam trapping is shown to be the limiting mechanism for further growth. In the case of the absolute instability a second nonlinear limit is obtained, where long term temporal oscillations were observed.
 Publication:

Ph.D. Thesis
 Pub Date:
 1975
 Bibcode:
 1975PhDT........41M
 Keywords:

 Physics: Fluid and Plasma; Energy;
 Electron Beams;
 Plasma Waves;
 Plasmas (Physics);
 Beam Plasma Amplifiers;
 Cerenkov Radiation;
 Computerized Simulation;
 Convection;
 Numerical Analysis;
 Plasma Oscillations;
 Plasma Physics