Electron energy distribution function (EEDF) analysis of negative hydrogen ion (H−) enhancement in a magnetized sheet plasma source

Abstract

Electron energy distribution functions (EEDFs) in a weakly magnetized sheet plasma have been measured for different Ar-H₂ gas mixtures by means of a Langmuir probe. Gas ratios were controlled by adjusting the neutral gas flow rate. EEDFs showed distinct electron groups (slow and fast) favorable for negative hydrogen ion formation. Changing the streaming neutral gas flowrate showed significant changes in the EEDFs which indicate the role of Ar in electron density (n_e) enhancement and of H₂ in effective electron temperature (T_eff) cooling. The effect of streaming neutral gas on H⁻ ion enhancement by changing streaming neutral H₂ flowrate is also reported. An ExB probe was used to measure the H⁻ ion current. Observations show that when Ar flow rate was kept at minimal changes, the negative ion current can be enhanced by 12.84% (6 cm from the center) up to as much as 135.48% (center) and 241.89% (3 cm from the center). Comparison of EEDF measurements for increasing streaming neutral H₂ flowrates reveals the shifting of the electron population from the high-energy region to the low-energy region. Production efficiency calculations show optimum H⁻ ion production at 2−4 cm where a balance between the slow and fast electron population occurs.