Technological and physical aspects of a constricted RF ion source

Experimental results are given for the perveance at different pressures and RF power using nitrogen and argon ions. The results are taken using a constricted axial RF ion source with an aspect ratio of the radius of the outlet aperture to the extraction gap width equals 0.4. Our data confirm the validity of the current scaling law at RF power equals 50 watt 20 watt in case of nitrogen and argon gases respectively at a pressure of 3 /spl mu/Hg. It is found that by increasing the pressure the beam current will decrease. Therefore, in order to keep the beam current constant, the RF power must be increased. In case of nitrogen, at a perveance of 0.24/spl times/10/sup -8/ Amp/V/sup 3/2/ corresponding to a pressure of 0.03/spl times/10/sup -8/ Amp/V/sup 3/2/ corresponding to a pressure of 25 /spl mu/Hg, it reduces to 1.2/spl deg/. In case of argon, at a perveance of 0.12/spl times/10/sup -8/ Amp/V/sup 3/2/ corresponding to a pressure of 3 /spl mu/Hg, the beam divergence is 7.2/spl deg/, while at a perveance of 0.02/spl times/10/sup -8/ Amp/V/sup 3/2/ corresponding to a pressure of 25 /spl mu/Hg, it becomes 3.2.