A BIASED OPTICAL PROBE METHOD FOR MEASUREMENTS OF ELECTRON-ENERGY DISTRIBUTION IN A PLASMA

A biased optical probe (BOP) method, i.e. novel technique for measurem ents of the electron energy distribution function (EEDF) in a range of such high energies as 10-50 eV has been developed. This method is bas ed on the optical emission induced by electrons passing through a nega tively biased mesh in a plasma. The BOP method was used to measure the EEDF in a do glow discharge in He/Xe mixture while the low-energy par t (< 10 eV) of the EEDF was measured using the conventional Druyvestey n method. The measured distribution function considerably deviates fro m an ideal Maxwellian distribution, because of abundant high-energy el ectrons generated in a cathode fall. On the contrary, the EEDF measure d in a low-pressure inductive rf discharge was found to follow a singl e Maxwellian distribution over a wide energy range.