Radial structure of two-stream instability in light ion beam

Two-stream instability induced by a uniform light ion beam of finite radius propagating in a background plasma is investigated numerically. Radial structure of the instability is obtained by a linear electromagnetic stability analysis. Problem is solved as an eigenvalue problem. Frequency and growth rate of the instability are obtained as the eigenvalues, and radial profile of perturbed physical quantities is obtained as the eigenfunction. Two types of the perturbation mode are obtained. One is that it's perturbation appears inside of the beam and is characterized by a radial mode number. Another is that the perturbation appears at the surface of the beam. It is also shown that although the growth rate increases with the radial mode number, it converges to a constant value for large mode number. (author)