OPTIMIZATION AND PERFORMANCE OF A SADDLE FIELD-ION SOURCE

The 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 and characterized the discharge with hydrogen in the oscillating ("low pressure") mode and in the transition mode. The anode design was optimized for maximum electrostatic confinement of the electrons and thus also maximum discharge current. A discharge current of 100 mA was obtained at a pressure of 0.5 Pa (3.8 mTorr) and a voltage of 10 kV. The discharge anisotropy was investigated and the discharge was found to be mainly an axial one in which the electrons oscillate near the axis. A highly peaked radial profile of current was measured at the end cathodes in the low pressure mode, and was dependent upon the operating pressure. A phenomenological explanation of these results is presented.