How does a Plasma Ball Work?

We've all seen them, with their mesmerizing glow, the fascinating play of the plasma lights on the glass. It's the proverbial lightning in a bottle. But where did the plasma ball come from, and how does is actually work?

The plasma lamp was invented by Nikola Tesla after his experimentation with high frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena. Tesla called this invention an Inert Gas Discharge Tube. They later went on to become known as plasma balls, plasma lights, Tesla balls, and luminglas, and are now very popular as decorative pieces for both home and office.

So how do these Tesla balls and luminglas work? The setup is fairly simple. A glass globe contains a metal electrode and is filled with gas, kept under an intermediate pressure. So how do we get the dancing plasma lights?

First, an electric voltage is applied to the metal electrode in the plasma ball. The electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit. By applying voltage to it, we create a stable electric field between the electrode and the glass globe. This stable electric field allows electrons to move through the gas, accelerating towards the glass of the plasma ball.

At the same time we apply the first voltage, we also create a second, oscillating voltage on the electrode. The alternating electromagnetic field that is produced by the shifting electric field keeps the free electrons moving inside the globe, and also helps contain the plasma when it forms.

So where does the plasma come from? It is created by the interaction between the free electrons and the gas inside the plasma ball. When electrons are given enough energy to break free from the cathode, they continue to accelerate within the plasma ball, eventually gaining many times the energy needed to ionize the gas. As they move around and ionize the gas, an ion trail is created.

This trail serves as a road for other electrons, making it easier for them to move along the same path, and creates the plasma streamer.

Inside this streamer, all the atoms and ions are bouncing around and colliding to reach an excited state. In order for the atoms to return to a lower energy state, some of the excess energy must be eliminated. One way of doing this is with a burst of light, called a photon, or in this case, the plasma light. The color of the plasma light depends on the atomic element.

 
Remember, too, that the entire plasma ball is kept under pressure. The higher pressure of the globe causes the atoms to pack together more densely, and the collisions between particles happens more frequently. The high energy particles collide to make the plasma. So what happens when the collisions occur with the far more numerous, lower energy, neutral particles? These collisions cause the ions to recombine with the free electrons and turn back into regular gas, and therefore contain the ions into a narrow, concentrated tendril of electrical discharge.

The electricity, contained within the tendril, heats the gas immediately around it, causing it to expand and become less dense than the rest of the gas in the plasma ball. As a result, the tendril floats gently upwards towards the glass, like hot air causing a balloon to rise, and forms the spectacular plasma light display with which we are so familiar.

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