Electrical Discharges Gallery
Here are some photographs of various unusual or interesting glow discharges. All
effects shown are easy to recreate, although various high voltage DC and RF power
supplies and a high-vacuum pump are required in most cases. Pressures, where
given, were measured with a very accurate capacitance manometer.
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Striated Discharges in Air
These photographs show two striated (banded) discharge modes in air with direct-current excitation. The glass discharge
tube is 1.5" in diameter and contains copper wire electrodes sealed into constrictions at each end. The cathode (-) is at the
top of the tube. In the image at right can be seen the typical striated positive column, Crookes dark space and other
features of the "normal glow" at a pressure of 0.12 torr. This mode draws very low currents at a relatively high voltage.
The image at left shows another striation effect, much more sensitive to conditions and much less stable than that of the
normal glow, occurring at 11.5 torr. This discharge draws substantial current and behaves more like an arc, with a low
voltage drop once "ignited." The tube becomes very hot in short order. It is possible, through very careful control of the
high voltage and the pressure, to obtain only two or three sausage-like striae widely separated in the tube. This mode
also has some nitrogen afterglow associated with it, which is easy to see by switching off the tube in darkness.