Design and fabrication of a spherical configuration ion source

We report a very simple ion source based on a glow discharge, where the cathode fall is used to accelerate ions; the applied voltage has therefore the purpose of both plasma generation and ion extraction, which makes construction and operation very simple. Discharge and ion beam characteristics of the spherical configuration ion source are studied at different experimental conditions. The ion beam current and gas flow pass through an orifice of small diameter which causes a mechanical confinement to focus the ion beam on the Faraday cup downstream of a distance of 3 cm. Experiments have been done with nitrogen as discharge gas. A disk of Bakelite insulator with different diameters (5, 10, 15, 20, 30 and 38 mm) has been put between the anode and the cathode. This disk covered the cathode area and reduced the discharge area on the cathode surface for discharge confinement; therefore, a higher output ion beam current could be obtained. The best working conditions were found to be at discharge pressure in the range of 10−4 mbar, gap distance between the cathode and the anode equal to 3 mm (insulator thickness) and orifice of the insulator diameter (Bakelite insulator) equal to 5 mm. Ion beam current of 230 μA was obtained at the optimum insulator orifice diameter of the Bakelite material (5 mm) for a nitrogen gas pressure of 5 ×10−4 mbar and a discharge current of 1 mA.