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2. Gaseous Conduction

Table of Contents:

1. Introduction
2. Gaseous Conduction
3. Glow Discharge
4. Sputter Coating
5. Operating Characteristics
6. Specification

If an inert gas such as argon is included in a cathode gas tube, the free ions and electrons are attracted to opposite electrodes and a small current is produced.

As the voltage is increased some ionisation is produced by collision of electrons with gas atoms, the 'Townsend' discharge. When the voltage across the tube exceeds the breakdown potential, a self-sustaining glow discharge occurs, characterised by a luminous glow.

Characteristics of Gaseous Discharge

Figure 1.

The current density and voltage drop remains relatively constant, the increase in total current being satisfied by the area of the glow increasing. Increasing the supply voltage increases current density and voltage drop; this is the abnormal glow region.

Further increase in supply voltage concentrate the glow into a cathode spot and arc discharge is apparent. The operating parameters of Sputter Coaters are within the glow discharge regions of the characteristic described.

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