A fluid approach to linear beam plasma electromagnetic instabilities

Electromagnetic instabilities found for an arbitrary oriented wave vector are typically difficult to investigate analytically within the framework of kinetic theory. The case of a small density relativistic electron beam interacting with a plasma is considered, and a two-fluid theory of the system including a kinetic pressure tensor is developed. The model obtained agrees very well with temperature effects found on oblique instabilities from a kinetic model, and the respective roles of parallel and transverse beam temperatures are correctly reproduced. An analysis of the phase velocities of the unstable waves allows for an explanation of this similarity. Such a formalism could be used to study oblique instabilities in settings where kinetic theory becomes problematic to implement.(c) 2006 American Institute of Physics.