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 ~150 μA at normal operating conditions (V_d=1.8 kV, V_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 ~310 μA for V_d ≃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 μA 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