Stimulated Raman scattering of a transverse magnetic (TM) mode in a strongly magnetised plasma

Abstract

A strongly magnetized plasma, e.g., the one encountered in a plasma filled backward wave oscillator (BWO), supports an obliquely propagating electromagnetic (EM) mode, k 0 ⊥ 2 = (k 0z 2 − ω 0 2 c 2 )( ω p 2 ω 0 2 − 1) where ω p 2 ⪡ ω c 2, ω p 2 ⪡ ω 0 2, ω 0 and k 0 are the pump wave frequency and pump wave vector, ω p and ω c are electron plasma and cyclotron frequencies, c is the speed of light in vacuum and z and ⊥ refer to the static magnetic field. As this mode acquires large amplitude it becomes susceptible to decay into a Trivelpiece-Gould (TG) mode and a sideband electromagnetic mode. The growth rate of the instability scales as γ ⋍ 1 4 υ osc k z( k z k ⊥ ) 1 2 ( ω p k 1c ) 3 2 , where υ osc is the electron oscillatory velocity, k and k 1 are the wave vectors of the low frequency electrostatic (ES) Trivelpiece-Gould mode and EM sideband wave. For typical BWO parameters the growth rate is of the order of the 10 9 s −1 range.