Suppression of decay instability of the non-resonant beat wave excited by two counter-propagating x-mode lasers in magnetized plasma

Abstract

The decay instability of non-resonant beat mode is investigated in homogeneous, hot, and collision less plasma having transverse static magnetic field. Two counter-propagating X-mode lasers with frequency difference ω1∼ω2≥2ωp and wave numbers k→1 and k→2 drive a non-resonant space charge beat wave at phase matching conditions of frequency ω0=ω1∼ω2 and wave numbers k→0=k→1+k→2. The driven beat wave acts as a pump for decay instability and parametrically excites a pair of lower hybrid wave (ω,k→) and sideband upper hybrid wave (ω3,k→3) propagating in sideward direction so that momentum remains conserved. The sideband wave couples with the driver beat wave to exert ponderomotive force on plasma electrons at frequency ω=ω0+ω3. The oscillatory motion of plasma electrons due to ponderomotive force and lower hybrid wave causes density perturbation in plasma, which couples with oscillating beat mode by feedback mechanism and gives rise to a sideband wave at resonance. The maximum growth rate is achieved at scattering angels θs∼30° and θs∼150°. The growth rate becomes half by changing applied magnetic field from ∼90 T to ∼270 T. The suppression of decay instability can be beneficial for parametric excitation of fast plasma wave (coupled with slow plasma wave) by two counter-propagating lasers for electron acceleration.