Parametric excitation of coupled fast and slow upper hybrid waves by counter-propagating circularly polarized lasers in a magnetized plasma

Abstract

The parametric decay of large amplitude non-resonant beating mode of counter-propagating lasers (having a frequency difference ≥2ωp) into a pair of upper hybrid waves is studied in magnetized plasma. One of the excited upper hybrid waves (known as fast wave) having phase velocity close to c, can be utilized for electron acceleration. The coupled mode equations of fast and slow upper hybrid waves are modelled by solving equation of motion and continuity equation simultaneously (using the density perturbation technique) to derive the dispersion relation for two plasmon decay process. The growth rate of the present excitation process using right circularly polarized beating lasers is higher as compared with the growth rates of the excitation processes using ordinary and extraordinary beating lasers. However, the growth rate is not significant in the case of left circularly polarized beating lasers. The growth rate ∼0.15ωps−1 is achieved for right circularly polarized beating lasers having v1,2/c=0.1 for scattering angle θs∼160° and applied magnetic field ∼90 T. The growth rate of fast upper hybrid wave was reduced with the applied axial magnetic field in the present case. The present work is not only significant for the electron acceleration by fast upper hybrid wave but also for diagnostic purpose.