User Rating: / 0
PoorBest 

• Experimental Apparatus
• The electron gun and the collimating apertures
• Gas cell and gas delivery system
• Vacuum chamber and attached instruments
• Electrostatic analyzer and Faraday cup combination
• Computer control interface
• Data collection procedure
• Experimental errors

Chapter two

Experimental Apparatus

2.1 Overview

The experimental arrangement was designed to measure the attenuation of the electron beam through a gas cell using the linear transmission technique to calculate the total electron scattering cross section. The schematic of the experimental arrangement is given in Figure 2.1. A beam of 100 – 4000 eV electrons, produced by an electron gun, was utilized to measure attenuation by the gas in the scattering chamber. A well-collimated narrow electron beam was obtained by passing the beam through three well-aligned apertures. The collimated beam entered the gas cell through the entrance aperture. Electrons emerging from the gas cell entered an electrostatic analyzer (ESA) which deflected the inelastically scattered electrons and passed the selected mono-energetic electrons. These electrons were collected at the exit aperture of the ESA with a Faraday cup. Intensity was measured with an electrometer. The ESA, gas cell, electron gun, and entire electron optics system were shielded from the earth’s magnetic field and other stray magnetic fields by using m metal. A differential pumping system was used along the beam transportation system to maintain a vacuum in the gas cell, electron gun region, and in the chamber where the ESA-Faraday cup combination is housed. Each item in the experimental setup is discussed below in detail.

Fig. 2.1 A schematic diagram of experimental setup.