Cathode ions impacting onto

Ions impacting onto the cathode during a discharge cause secondary electrons and other charged and neutral species from the electrode material to be ejected. Some of these other particles derived... 

Impact of excited atoms onto the cathode (similar to the electron release caused by ions)... 

The ion beam is produced in the following way U atoms are evaporated from an oven at a temperature of typically 400 C, and are ionized and excited to the metastable 2 5 state by electron impact, when leaving the oven aperture. The electrons are emitted from a little ring-shaped tungsten wire cathode which is placed horizontally several millimeters above the oven exit. The cathode is held at ground potential, the oven at +200 V. The electrons are accelerated directly onto the oven aperture thus counterpropa-gating to the ions which are accelerated in the same electric field. The ions pass the cathode loop and are formed into a well-collimated beam by an electrostatic lens system. 

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