Effect of negative oxygen ions on the characteristics of plasma in a cylindrical DC discharge

Langmuir probe measurements are performedin cylindrical dc glow discharge plasma. Plasma wasgenerated in an evacuated glass tube, with circular planedisk electrodes. Measurements were carried out at differentpoints along the axis of tube for different working pressuresof pure argon and mixture of argon–oxygen gasses toobtain the plasma density and temperature as well asplasma and floating potentials. Variation of dischargepotential as a function of discharge pressure for bothplasmas is observed. It is shown that electron temperature,plasma potential, and floating potential in constant currentmode and constant pressure are increased from cathode toanode on the axial points of the discharge tube, whileelectron density is decreased. To sustain the dischargeprocess after adding oxygen to plasma, higher voltage isrequired since electrons are more energetic at lowerdensity.