Fig.7(b) shows the characteristics of the electric field inside the ion collector when 40 V was applied at the inner elec-trode. It was observed that the electric field was distributed with the highest strength near the head and end of inner electrode whereas electricfield decreased in magnitude from the edge of the inner electrode to the outer electrode of the collector. It was also found that the holder insulator of the inner electrode could be used to change the distribution and uniformity of the electricfield in the collecting zone as shown inFig.7(b).