Electromagnetic Mode in Counterstreaming Plasmas in a Magnetic Field

Electromagnetic waves propagating across an external magnetic field are investigated for a system composed of two identical counterstreaming electronic plasmas. Using the cold-plasma equations, it is found that the extraordinary wave is unaffected by relative streaming, while the ordinary wave is modified. The modified ordinary wave remains linearly polarized, but becomes dependent on the magnetic field. It has two propagation bands, one of which can be below the plasma frequency. This mode becomes unstable if the ratio of plasma frequency to electron gyrofrequency exceeds one-half the ratio of light velocity to relative streaming velocity. Brief discussion is given on the general case of nonidentical streams.