A Penning-type ion source with an expansion cup for impact processes

An ion source designed to perform ion-impact studies in the energy range up to 10 keV is described. It is a magnetically confined, oscillating electron-bombardment type with a cold cathode and expansion cup. It gives a helium ion current of approximately 150 mu A at normal operating conditions (V/sub d/=1.8 kV, V/sub e/=5 kV, and magnetic field=80 G). Measurements have been carried out to find the influence of pressure, discharge voltage, magnetic field, and extracting voltage on the ion-source properties. The ion beam is significantly increased with discharge voltage up to approximately 310 mu A for V/sub d/ approximately=3 kV. However, it is less affected with extracting voltage. At low pressure, the beam is influenced by the magnetic field to give a current increase of 30 mu A through the magnetic range up to 135 G, while it is almost unaffected by the magnetic field at high pressure. It showed an energy spread of 32 eV at a discharge voltage of 1.8 kV and an extraction voltage of 2 kV.<
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