4. DC discharge

Applying a DC voltage between two electrodes in a gas tube remains a classic method for producing a discharge. For example, we use a glass tube a few centimetres in diameter, fitted with electrodes at both ends, and filled with a gas at medium pressure, of the order of 1 torr.

A DC potential difference V is applied across the tube through a load resistor R _c by an electromotive force generator V ₀ . By acting on R _c and V ₀ , the current I flowing through the gas can be varied from very low values, of the order of 10 ^-18 A, up to some 10 A. Each value of I corresponds to a value of V, defining a current-voltage characteristic of the discharge,...