Plasma globe

Plasma globes, or plasma lamps (also called plasma balls, domes, spheres, tubes or orbs, depending on shape), are novelty items that were most popular in the 1980s.^[1] The plasma lamp was invented by Nikola Tesla^[2] after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena, but the modern versions were first designed by Bill Parker.^[1] Tesla called this invention an inert gas discharge tube.^[3] 

Working principle

Most commonly, plasma globes are available in spheres or cylinders. Although many variations exist, a plasma lamp is usually a clear glass orb filled with a mixture of various gases (most commonly neon, sometimes with other noble gases such as argon, xenon and krypton) at nearly atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 2–5 kV, generated by a high-voltage transformer. A much smaller orb in its center serves as an electrode. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge).

Placing a hand near the glass offers an attractive place for the energy to flow. The capacity of the body to accept radio-frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. The energy is flowing through the filaments, so the filaments move too. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.^[1] The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object the size of a human. The filament is thinner because the magnetic fields around it, augmented by the now-higher current flowing through it, causes a magnetohydrodynamic effect called self-focusing: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself.

An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in a capacitor formed between the ionized gas and the hand.

The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments.

The neon available for purchase for a neon-sign shop often comes in glass flasks at the pressure of a partial vacuum. These can not be used to fill a globe. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gasses involved.

Of the noble gasses, radon is radioactive, helium escapes through the glass too quickly, and krypton is quite expensive. Other gasses can be used. The plasma will take apart any molecular gas.

Caution

Caution should be taken when placing electronic devices near or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge on the device, even through a protective plastic casing. The radio frequency field produced by plasma lamps can interfere with the operation of touchpads used on laptop computers, digital audio players, cell phones, and other similar devices.^[1] Some types can radiate sufficient RFI to interfere with cordless telephones and Wi-Fi devices several feet away. If a medium-sized lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens of milliamperes to ground through the foil, enough to light a small lamp or give a small arc burn. This is possible because the glass acts as a capacitor dielectric: the inside of the lamp acts as one plate, and any conductive object on the outside acts as the other capacitor plate.^[3] Ozone, which is harmful to humans, may also accumulate outside of the surface of the glass orb after a few minutes of constant operation.^[1]

Plasma globe

Plasma globes, or plasma lamps (also called plasma balls, domes, spheres, tubes or orbs, depending on shape), are novelty items that were most popular in the 1980s.^[1] The plasma lamp was invented by Nikola Tesla^[2] after his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena, but the modern versions were first designed by Bill Parker.^[1] Tesla called this invention an inert gas discharge tube.^[3] 

Working principle

Most commonly, plasma globes are available in spheres or cylinders. Although many variations exist, a plasma lamp is usually a clear glass orb filled with a mixture of various gases (most commonly neon, sometimes with other noble gases such as argon, xenon and krypton) at nearly atmospheric pressure. They are driven by high-frequency alternating current at approximately 35 kHz, 2–5 kV, generated by a high-voltage transformer. A much smaller orb in its center serves as an electrode. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light (see corona discharge and electric glow discharge).

Placing a hand near the glass offers an attractive place for the energy to flow. The capacity of the body to accept radio-frequency energy is greater than that of the surrounding air. The energy available to the filaments of plasma within the globe will preferentially flow toward the better acceptor. The energy is flowing through the filaments, so the filaments move too. This flow also causes a single filament, from the inner ball to the point of contact, to become brighter and thinner.^[1] The filament is brighter because there is more current flowing through it and into the 150 pF capacity, or capacitance, presented by an object the size of a human. The filament is thinner because the magnetic fields around it, augmented by the now-higher current flowing through it, causes a magnetohydrodynamic effect called self-focusing: the plasma channel's own magnetic fields create a force acting to compress the size of the plasma channel itself.

An electric current is produced within any conductive object near the orb. The glass acts as a dielectric in a capacitor formed between the ionized gas and the hand.

The globe is prepared by pumping out as much air as is practical. The globe is then back-filled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the globe is "struck" or "lit", now, the whole globe will glow a diffuse red. If a little argon is added, the filaments will form. If a very little xenon is added, the "flowers" will bloom at the ends of the filaments.

The neon available for purchase for a neon-sign shop often comes in glass flasks at the pressure of a partial vacuum. These can not be used to fill a globe. Tanks of gas, each with its specific, proper, pressure regulator and fitting, are required: one for each of the gasses involved.

Of the noble gasses, radon is radioactive, helium escapes through the glass too quickly, and krypton is quite expensive. Other gasses can be used. The plasma will take apart any molecular gas.

Caution

Caution should be taken when placing electronic devices near or upon the plasma lamp: not only may the glass become hot, but the high voltage may place a substantial static charge on the device, even through a protective plastic casing. The radio frequency field produced by plasma lamps can interfere with the operation of touchpads used on laptop computers, digital audio players, cell phones, and other similar devices.^[1] Some types can radiate sufficient RFI to interfere with cordless telephones and Wi-Fi devices several feet away. If a medium-sized lamp is wrapped in grounded metal foil, capacitive coupling can transfer tens of milliamperes to ground through the foil, enough to light a small lamp or give a small arc burn. This is possible because the glass acts as a capacitor dielectric: the inside of the lamp acts as one plate, and any conductive object on the outside acts as the other capacitor plate.^[3] Ozone, which is harmful to humans, may also accumulate outside of the surface of the glass orb after a few minutes of constant operation.^[1]