Lamp with plasma

Constitution

The lamp is generally a large transparent hollow sphere of about thirty centimetres in diameter, filled with rare gas under low Pression equipped with a small sphere full for the center playing the part with electrode. Strong a electric Tension alternative is applied between the two spheres. The frequency lies between 10 Khz and 60 Khz.

The gas inside is generally a mixture of inert gases, often of the Néon and Xenon. According to the mixture the colors obtained are different, but the lamps sold in the trade are generally blue-lavender-pink orange.

Operation

The principle of operation of a lamp with plasma is connected with that of a Electric shock with barrier Diélectrique. The high voltage applied to the central electrode will generate a Electric field high in the volume of gas under low pressure between the two spheres of glass. The surrounding medium, whose potential is of zero volt, plays the part of second electrode.

The electric field created accelerates the free electron S present in the enclosure of the lamp, which will cause an electron avalanche due to the Ionization of the gas atoms by electronic impact. This avalanche grows exponentially of density of loads, finally giving rise to an electric shock between surfaces of the spheres of glass. This phenomenon of Claquage transforms gas insulating into plasma conducting (ionized gas) and luminous.

The presence of dielectric interfaces (glass) between the electrodes makes that the electric shock is only temporary. The ions and the electrons directly not being able to reach the electrodes, they will accumulate gradually on the surface of each of the two spheres (positive ions towards cathode and the electrons towards the anode). It arrives one moment when surface density of load écrante potential of the central electrode, which will have as a consequence the fall of the electric field in the lamp, and finally the extinction of the discharge in a few microseconds.

The application of a tension alternatively positive and negative to the central electrode allows a periodic inversion of the electric field in the enclosure of the lamp. This allows the maintenance indeed is of an alternative or pulsated continuous electric shock, coupled capacitivement with the electrodes (that of the lamp, in the center, and the surrounding ground). The walls of lamp glass thus behave like condensing , whose impedance is inversely proportional to the frequency of the tension applied. All equal things, the current circulating between the central electrode and the environment (with the potential of the ground) being conversely depend on the impedance of the spheres of glass, plus the frequency applied are high and more the electric shock is intense.

When the sphere is touched, one locally increases the capacitive coupling of the environment to the sphere of glass, thus making fall the impedance of the system at the place of the contact. It results from it that the current (of displacement and conduction) is higher and gives place to a more intense electric shock.

Safety

The electric Tension delivered in the center is roughly ~10 000V but the electric current remains very weak.

Important:

not to touch metal at the same time. Risk shock.
not to touch uninterrupted the sphere, it heats and can yield.
to maintain distant from loudspeakers and electronics components.

See too

Lamp with lava

External bond

a lamp with plasma in action

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