Influence of Nitrogen Seeding on the Electron and Ion Behaviors in Helicon Wave Excited Argon Plasma

The effect of nitrogen gas seeding on electron density, electron energy probability functions (EEPFs), ion energy distribution functions (IEDFs) and ion species concentrations downstream of an argon helicon wave plasma (HWP) beam is investigated by Langmuir probe, electrostatic quadrupole plasma analyser and optical emission spectroscopy. Neutral depletion is found at axial location Z = 45 cm downstream of the HWP source, which can suppress the electron loss and cooling at the axis caused by N2 seeding. As the axial location increases to Z = 57.5 cm and then to 70 cm, neutral depletion becomes slight and the addition of N2 can effectively modulate the electron density and EEPFs. IEDFs results indicate a decrease of the average ion energy with an increase of nitrogen admixture, which is consistent with the sheath voltage fall estimated based on the electron temperature and the proportion of each ion species. Moreover, compared with Ar+ ions, the IEDFs of N2+ and N+ ions present a shift towards the higher energy region, due to the radio frequency oscillating sheath effects