Electron Scattering Cross Sections Experimental Apparatus: : The electron gun and the collimating apertures

2.2 The electron gun and the collimating apertures

A Kimbal Physics Model EGG-3101 electron gun was used to produce the electron beam in the energy range 100 – 4000 eV. This gun produces electrons using thermionic emission. It uses a refractory metal thermionic emitter consisting of a disk mounted on a hairpin filament that emits electrons when the filament wire is heated by the voltage source. This cathode is directly heated by an isolated voltage source. The voltage source is control by an energy supply, a negative high voltage supply (100 to 10000 eV) with reference to ground.

The gun is equipped with a beam focusing device and beam deflection plates. Neither of these devices were used in the present experiment since the experiment was design to perform with 100 pA electron beam current. For the entire energy range (100 – 4000 eV) a stable 100 pA beam current, as measured by the ESA-Faraday cup combination, could be obtained by applying 40 mA or less emission current to the filament. The electron beam emerging from the gun passed through three well-aligned 0.76mm diameter apertures, spaced 2 cm apart, to collimate the electron beam.