ABSTRACT
The Penning ion source got its name, Penning, Ionization Gauge (PIG), from F. M. Penning who invented the Penning or Philips Ionization vacuum Gauge in 1937. Penning ion sources were first used as internal sources in cyclotrons in the 1940s. Cyclotron versions usually have longer anodes because of the larger gap of cyclotron magnets. Ions can be extracted from PIG ion sources axially through one cathode or, more commonly, radially through a slit in the anode. PIG sources can be operated in dc or pulsed mode, depending on the operational mode of the accelerator and on the power level needed to generate a specific ion beam. PIG sources with axial ion extraction give lower currents of multiply charged ions for several reasons. If a high-current mode of operation is used in a PIG with axial extraction, an expansion cup improves the beam formation and quality.
