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~~[MERIT]~~ · 08-15-2012, 09:27 PM

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Figure 1 shows a typical experimental gas discharge tube consisting of cathode and anode electrodes at opposite ends of a sealed, gas-filled, glass vessel. When a voltage is applied, a region of non-fluorescence known as the Faraday Dark Space extends from the cathode for a distance that depends mainly on the gas pressure. Then, at a fairly sharply defined boundary marking where the accelerating electrons have enough energy to excite the gas molecules, the "Positive Column," or "Glow Discharge" region begins, and extends to the anode. In a commercial fluorescent tube the design parameters are arranged to minimize the dark space at the cathode, so that the glow fills virtually the entire length. The reddish glow of the Sun's chromosphere, closer in where the converging field lines create an intensifying field, is strongly suggestive of a glow discharge region. This is also consistent with the appearance of "red giant" stars, where a chromosphere viewed from afar would give a bloated appearance if the supply current were sufficiently low for nothing more spectacular to be happening inside.

To maintain a steady discharge, the anode must collect an uninterrupted stream of sufficient electrons to carry the current--charge moved per unit time--flowing in the full cross-section of the discharge plasma. Particles in the discharge plasma posses two kinds of motion. First are random, or thermal, motions reflected in the measure of internal energy or "temperature," in which the less massive particles move faster. Superposed upon these is a steady drift current imposed by the electric field, comprising the combined effects of electrons impelled toward the anode and ions toward the cathode. The random motions of the fast-moving electrons are typically much more energetic than their drift motions and create complications for the anode trying to maintain a stable discharge.