Ambipolar Diffusion in Direct-Current Positive Column with Variations in Radius of Discharge Tube

The ambipolar diffusion and argon ion mobility as functions of the reduced electric field and pressure times the tube radius are investigated in a weakly ionized non-uniform glow discharge plasma system. In particular, the variable cross section at the same discharge tube on the ambipolar diffusion coefficient shows a more noticeable effect than the effects from the ion mobility. As the diffusion length Λ increases, the ambipolar diffusion D_a increases. However, it decreases as the discharge current is increased.