Abstract :
A NECESSARY condition for the initiation of an electric discharge between two electrodes immersed in a gas is that the voltage difference between the electrodes be greater than a critical value called the breakdown voltage. The nature and pressure of the gas and the shape, separation, and nature of the electrodes determine this critical value. When a gas tube breaks down or fires, a positiveion space charge is formed so that electrons can flow in great quantities without the limitations of mutual repulsion. A self-sustaining discharge in a cold-cathode tube requires, in addition, a positiveion current sufficiently heavy to provide for electron emission from the negative electrode or cathode.
