Convective Instability of the Bernstein Wave Propagating Obliquely to the Magnetic Field in a Beam-Plasma System

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Abstract
The Bernstein wave propagating obliquely to the magnetic field is excited by the coaxial probe and is heavily damped by the Landau and/or cyclotron damping with respect to the direction along the field, whose propagation direction may be coincident with that of the maximum value of group velocity (∂ω/∂ k ). When a rather weak electron beam is injected, the wave is amplified due to the convective instability, whose wave vector k is determined as follows: the wave number component k ∥ paralell to the field satisfies the Cherenkov excitation condition ( k ∥ υ b ≈ω), and then, the component k ⊥ perpendicular to the field is determined by the dispersion relation K (ω, k ∥ , k ⊥ )=0. Increasing the intensity of the electron beam above the threshold value, the spontaneous excitation of the wave is observed, which can be explained consistently as the result of the convective instability of thermal noise in plasma.

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