MadSci Network: Physics |
Dear Matt:To answer your question I will first tell you about making the plasma. The simplest way to start is to talk about a neon sign. This is a glass tubing sealed with neon gas inside at a low pressure. There are two electrodes inside the tube, so that a voltage can be applied across tha gap between the electrodes. This voltage causes an electrical breakdown in the gas, just like a lightning bolt is an electrical breakdown in the air at atmospheric pressure. In the sign, the gas begins to glow and the sign is lit up. Inside the gas there are negative electrons and positive neon ions created by the breakdown. As long as the voltage remains on the electrodes these positive and negative particles in the gas will be colliding with each other and the neon atoms become electrically excited and emit the light light the sign. As long as the voltage remains on the electrodes a current will flow, through the electrically charged gas between the electrodes and consume power. As soon as you take away the volage on the electrodes the neon plasma will disappear because there is no longer an electrical field between the electrodes to keep the gas ionized and conducting. The gas then returns to its original state, no glow, and just back to being a gas like it was before the plasma was ignited! For neon gas this is a simple situation because neon is chemically inert, so there is no change in the properties of the gas. However, if you put a gas in the tube which becomes chemically reactive when in the plasma state, like methane (CH4) it is quite possible that chemical reactions will take place within the plasma and the chemical structure of the gas mixture may be changed, so when you turn off the plasma you may have a differnt chemical gas in the chamber. However it will still be a gas! Dick Bersin......
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