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.