[6.5.4] An electric discharge characterized by a low, approximately constant current density at the cathode (on the order of 10 µA/mm2), at low cathode temperature, and a large voltage drop (typically 50 volts or more). Secondary emission from the cathode is much greater than the thermionic emission.

Note: A distinction is made between the normal cathode drop (potential difference due to space charge near the cathode) that occurs when the glow does not cover the cathode completely (with constant current density) and which is independent of the discharge current, and the abnormal cathode drop that occurs when the glow covers the cathode completely (with increased current density) and which depends on the discharge current.

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