Plasma

Fire Poi*

Fire is hot. We don’t usually think about it being hot; it’s more instinctive or reflexive knowledge, but fire is actually hot enough to be weird. It was humanity’s very first source of plasma and in the thousands of years that fire held a monopoly on anthropogenic ionized gasses it became deeply symbolic. A primal source of fear. A symbol of power and purity. A source of childish wonder. And, as our very first controlled chemical reaction, and unmistakable sign of humanity’s growing knowledge about our world.

First some quick definitions:
Oxidation is the removal of electrons from a material. It derives the name from the fact that it is commonly accomplished by combining materials with oxygen, well known for electron thievery.

http://en.wikipedia.org/wiki/File:Fire.JPG

This is fire. You’ve probably heard of it, actually.**

Fire is the 1) oxidation of some material in a fashion that 2) produces energy and 3) proceeds rapidly enough that the energy released sustains the reaction in conditions where it would otherwise not proceed. In shorter terms; fire is an oxidative exothermic chain reaction.
Flames are short-lived quantities of plasma resulting from the extraordinary temperature of combustion products and/or incomplete combustion of fuel.
Plasma is a diffuse state of matter like a gas that has been ionized; typically by extreme temperature but occasionally by some other means. My own weak grasp of modern physics has left some ambiguity as to whether plasma requires that electrons be independent of their home atoms or merely very highly excited (and some additional ambiguity as to what the difference would be in a diffuse gas). At the very least I can say that ‘free’ electrons are a common feature of plasmas. What do I mean by ‘free’ electrons? Remember our energy diagram? One way in which an atom can absorb energy is to push electrons away from the nucleus. The separation of the positive charge in the nucleus and the negative charge of the electron stores potential energy. Push the electron far enough away and it starts to act on its own rather than as part of an atom. Incidentally, when those electrons go crashing back down toward the nucleus that potential energy can be released as a photon, which is why fire glows.

Back to definitions.
Ionization is the separation of electrical charge into separate particles. The violence involved in this process depends on the state of matter in which it occurs. In liquid (especially polar liquids like water), it is relatively easy to accomplish because the charges need not be separated by great distances and can be shielded (or at least insulated) from each other by other particles. In a gas (as when making plasma) the process requires significantly more energy due to the increased distance of separation and the comparative lack of shielding/insulation available.

So what good is plasma, apart from being a really cool toy that we can legitimately refuse to give to our children but still play with ourselves? Well, free electrons and such are really reactive and can generate some ions that would otherwise be rare. I’ve talked before about ionized oxygen.  Short version; it’s bloody effing murder to anything it touches. But since ionized oxygen species are perhaps the most reactive chemicals most of us will ever encounter, they don’t really last all that long. Certainly not long enough to cross through layers of human tissue for example. So plasma would make a really badass disinfectant; selective for microbes on the surface without risking any deep tissue damage. (Screw your Lysol. I have electrons.) If only there were some way to apply it to humans without all the hotness and burning.

Oh wait. We can. While fire is a very good way to make plasma, we broke the plasma monopoly a little over a hundred years ago with the cathode ray. Since then, we’ve figured out how to make it without being hot. Want to disinfect your skin? Maybe soon you will just be able to pour it on.

http://es.wikipedia.org/wiki/Archivo:Lightning_struck_tree_1.jpg

Tree vs. Lightning. Lightning wins.***

Of course, not all plasma is under control. Lightning is a wild and powerful force that can do phenomenal damage. First it electrocutes your tree, then hits you with a pressure wave from the thunder, then it explodes your tree by boiling it from the inside out.  If you happen to have a seismograph on hand, you get a really good idea of how that plays out.

So what to do? Lightning rods are so 18th century. We know more of plasma than we did then. We know that the potential energy released in lightning is due to charge separation. We know that plasmas consist of separated charge particles. We know that separated charged particles conduct charge better than inert gasses. This is not only really cool when you get a fire going between power lines (don’t try this at home), but it has practical implications.

http://terahertzatheist.ca/wp-content/uploads/2009/03/laserlightning.jpg

‘Laser guided electrical filament’- Just call it a lightning cannon. ****

The plan? Shoot lasers at the sky! What will this accomplish? The gas in the path of an intense laser converts into plasma. The plasma provides a conductive channel to relieve the charge separation between clouds and ground, controlling the location of the lightning strike. Keen observers might note that this technology also enables us to build lightning cannons.

Humanity has cowered in fear of plasma for as long as we have known it (and we still do). But the things we fear are often really cool. And when we watch and learn, see how far we come.

Image sources:
*http://en.wikipedia.org/wiki/File:Maitre_du_feu.jpg
**http://en.wikipedia.org/wiki/File:Fire.JPG
***http://es.wikipedia.org/wiki/Archivo:Lightning_struck_tree_1.jpg
****http://terahertzatheist.ca/wp-content/uploads/2009/03/laserlightning.jpg

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