THEORETICAL MODELLING OF KELVIN HELMHOLTZ INSTABILITY DRIVEN BY AN ION BEAM IN A NEGATIVE ION PLASMA

An ion beam propagating through a magnetized plasma having positive ions K+ (Potassium ions), electrons and negative ions SF6 (Sulphur hexafluoride ions) drives Kelvin Helmholtz Instability (KHI) via Cerenkov interaction. For two modes, K+ and SF6 , the frequency and the growth rate of the unstable wave increase with the relative density of negative ions. It is observed that the beam has destabilizing effect on the growth rate of KHI in the presence of negative ions. However, at the large concentration of the negative ions beam stabilizes the growth rate of KHI. An increase in mass of negative ions also stabilizes the growth rate of KHI modes. It is also observed that increase in ion beam velocities and densities play a significant role in changing the growth rate of KHI modes. Moreover, the finite geometry effects tend to modify the dispersion properties and growth of KHI modes.