15.1.1.2 Negative Pulseless Glow
The negative pulseless glow mode is characterized by a pulseless discharge current. As indicated by the
well-defined visual aspect of the discharge (Fig. 15.2b), the discharge itself is particularly stable, which
shows the basic characteristics of a miniature glow discharge. Starting from the cathode, a cathode dark
space can be distinguished, followed by a negative glow region, a Faraday dark space and, finally, a
positive column of conical shape. As with low-pressure glow discharges, these features of the pulseless
glow discharge result from very stable conditions of electron emission from the cathode by ionic
bombardment. The electrons, emitted with very low kinetic energy, are first propelled through the
cathode dark space, where they acquire sufficient energy to ionize the gas, and intensive ionization
occurs at the negative glow region. At the end of the negative glow region, the electrons lose most of their
kinetic energy and are again accelerated across the Faraday dark space before they can ionize the gas
atoms in the positive column. The conical shape of the positive column is attributed to the diffusion of
the free electrons in the low-field region.
0.5 cm0.3 cm(a)(b) (c)0.5 cmFIGURE 15.2 Corona modes at cathode: (a) Trichel streamers; (b) negative pulseless glow; (c) negative streamers.
Cathode: spherical protrusion (d¼0.8 cm) on a sphere (D¼7 cm); gap 19 cm; time exposure 1=4 s. (From Trinh,
N.G. and Jordan, I.B.,IEEE Trans., PAS-87, 1207, 1968; Trinh, N.G.,IEEE Electr. Insul. Mag., 11, 23, 1995a. With
permission.)