Axisymmetric instabilities of fast electron beams in dense plasmas

Axisymmetric radial modes of fast electron beams propagating through dense background plasmas with a return current are studied in a two electron-fluid model. The linear growth rate is obtained by numerically solving the self-consistent electron fluids system. The dispersion relation is also calculated for certain parameters. It is found that various radial modes are excited over the entire range of axial wavelengths, as the long-wavelength regime is dominated by hollowinglike modes characterized by an azimuthal number of m=0 and radial numbers of n=2 and n=3, and the short-wavelength regime is dominated by electromagnetic beam-plasma instabilities with higher radial mode numbers. Also, it is found that the finite beam-plasma temperatures, collisional effects and strongly asymmetric density conditions, with density of the beam being much less than the plasma density, can significantly reduce the growth rate of the instabilities. (c) 2008 American Institute of Physics.