Editing Plasma globe (section)

== Construction ==
Although many variations exist, a plasma ball is usually a clear glass sphere filled with a mixture of various gases (most commonly [[neon]], sometimes with other [[noble gas]]es such as [[argon]], [[xenon]] and [[krypton]]) at nearly atmospheric pressure. 

Plasma balls are driven by high-frequency (approximately {{nowrap|35 [[hertz|kHz]]}}) [[alternating current]] at {{nowrap|2–5 [[volt|kV]]}}.<ref name=Gache/> The drive circuit is essentially a specialized [[power inverter]], in which current from a lower-voltage DC supply powers a high-frequency [[electronic oscillator]] circuit whose output is stepped up by a high-frequency, high-voltage [[transformer]], for example a miniature [[Tesla coil]] or a [[flyback transformer]]. The radio-frequency energy from the transformer is transmitted into the gas within the ball through an electrode at its center. Additionally, some designs utilize the ball as a resonant cavity, which provides positive feedback to the drive transistor through the transformer. A much smaller hollow glass orb can also serve as an [[electrode]] when it is filled with metal wool or a conducting fluid that is in communication with the transformer output. In this case, the radio-frequency energy is admitted into the larger space by [[capacitive coupling]] right through the glass. [[Plasma (physics)|Plasma]] filaments extend from the inner electrode to the outer glass insulator, giving the appearance of moving tendrils of colored light within the volume of the ball {{Crossreference|(see [[corona discharge]] and [[electric glow discharge]])}}. If a hand is placed close to the ball it produces a faint smell of [[ozone]], as the gas is produced by high voltage interaction with atmospheric oxygen.

Some balls have a control knob that varies the amount of power going to the center electrode. At the very lowest setting that will light or "strike" the ball, a single tendril is made. This single tendril's plasma channel engages enough space to transmit this lowest striking energy to the outside world through the glass of the ball. As the power is increased, this single channel's capacity is overwhelmed and a second channel forms, then a third, and so on. The tendrils each compete for a footprint on the inner orb as well. The energies flowing through these are all of the same polarity, so they repel each other as like charges: a thin dark boundary surrounds each footprint on the inner electrode.

The ball is prepared by pumping out as much air as is practical. The ball is then backfilled with neon to a pressure similar to one atmosphere. If the radio-frequency power is turned on, if the ball is "struck" or "lit", now, the whole ball will glow a diffuse red. If a little argon is added, the filaments will form. If a very small amount of xenon is added, the "flowers" will bloom at the ends of the filaments.{{citation needed|date=November 2012}}

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

Of the other noble gases, [[radon]] is [[radioactive]], [[helium]] escapes through the glass relatively quickly, and [[krypton]] is expensive. Other gases such as [[Mercury (element)|mercury]] vapor can be used. Molecular gases may be dissociated by the plasma.