Influence of N₂ admixture on mode transition of discharge in N₂-Ar helicon plasma

Effects of N₂ admixture on multiple wave modes and transitions were investigated in N₂-Ar helicon plasma under fixed input power and magnetic field. The structures of helicon waves were measured by a B-dot probe to verify the different eigenmodes. The experimental results show that the plasma morphology, emission spectrum, and spatial profile change significantly during mode transitions with the N₂-Ar ratio. The calculated results from the pressure balance model indicate that the densities of species N₂, N⁺, Ar, and Ar⁺ will change largely during mode transition around some specific N₂ percentages, which will help to improve the application of N₂-Ar helicon plasma in material processing greatly.