Optimization of cold cathode saddle field ion source

The modified cold cathode saddle field ion source operates at low gas pressure and requires neither magnetic field nor filament. We have designed a cold cathode saddle field ion source (cylindrical symmetry type) and characterized the discharge with nitrogen gas in the oscillating (“low pressure'') mode. The distance between the two anode rods was optimized for maximum electrostatic confinement of the electrons. The discharge anisotropy was investigated and the discharge was found to be mainly an axial one in which the electrons oscillate near the axis at the discharge region. A high output beam current was measured on the Faraday cup at a distance of 1.5 cm from the cylindrical cathode, and was found to be dependent upon the operating pressure and the discharge current. An ion beam current of 220 μA was obtained at the optimum distance between the two anode rods of 6 mm for a nitrogen gas pressure of 8×10−4 mbar and a discharge current of 2 mA.