Theory of Operation

An evacuated glass comainer is sealed and pumped to.5 to 2 Torrs of pressure. A metal cap seals the con-

tainer and serves as an electrode for charging the remaining thin gas mixture. The voltage applied to the cap is at a potential of 10 to 20 thousand volts and is at a high frequency of approximately 25 kHz. The capacitive effect of the thin gas causes a current to flow, creating the plasma discharges. One may visual­ize the device in the following manner: A capacitor is formed by the conductive gas inside the container forming one plate, the glass envelope being the insu­lating dielectric and the outer air serving as the other plate. Any conducting object brought near the con­tainer now only enhances this effect and appears to draw the plasma arc to the point of contact.

The vacuum will vary along with the physical parameters of the container and can be adjusted to enhance the type of discharge desired. A pressure where the plasma discharges are most defined may be critical. Increases will create a broken, wispy effect, whereas a further decrease will broaden the discharge and eventually form striations as a series of weird, orange disks. Any weird effects are possible from changing pressure, power frequencies, and voltage.

The effect of where the conduction of a gas peaks at a certain pressure is known as the Townsend effect and becomes an important factor in the design of vacuum systems where medium – to high-voltages are encountered. The device as described does not use any gas other than the existing atmosphere rarefied by evacuation. Other colors and effects are limitless when the builder chooses to charge the unit with other gases or combinations of pressures.

Project Description

The described device is intended for display pur­poses, novelty decorations, and special effects, as well as an educational science fair project demonstrating plasma that is controlled electrically and magneti­cally. Special materials treated by a controlled plasma beam can also be realized.

Plasma is often considered lo be the fourth state of matter. It consists of atoms that are ionized and

demonstrates peculiar effects unlike the other three forms of matter.

Columns of pinkish and purplish plasma are attracted to external influences such as fingers and other objects when placed on or near the display con­tainer. These columns of plasma light span the entire length of the display container, dancing and writhing with a tornado-like effect. Balls of plasma and fingers are created and controlled by simply touching the container. This effect cannot be effectively or justifi­ably described in words and can only be appreciated when actually observed.

The device is low powered, high frequency, and high voltage, producing the necessary parameters for obtaining the described plasma effect. This generator utilizes conventional electrified circuitry, consisting of a transistor switching the ferrite core of a high-volt­age resonant transformer (similar to a TV flyback). Power for the transistors is obtained from a simple step-down transformer and rectifier combination.

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