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danzibr
2013-07-17, 07:20 PM
I was reading about plasma on wikipedia but was left wanting. I figured I'd see if we have any physicists in the playground.

Wikipedia mentions cold plasma, plasma existing at nearly 0 Kelvin. Usually I think of plasma as being hot, like lightning. Can you have plasma at, say, room temperature? Or can it *just* be really hot or really cold (depends on what it's made out of, I suppose, like mercury being liquid at room temperature)?

Suppose you could have plasma at room temperature. Would it dissipate into the air or be more like water where you could set it in a bowl? What would it feel like if you could put it in a bowl? For some reason I picture it as being kind of like... this:
http://www.wizards.com/magic/images/cardart/MRD/Nightmare_Lash.jpg
If hot plasma were to contact water what would happen? Would it evaporate the water? How about if it were to touch wood? Would it set the wood on fire?

Just trying to better understand the fourth phase of matter. Thanks!

AsteriskAmp
2013-07-17, 07:40 PM
I was reading about plasma on wikipedia but was left wanting. I figured I'd see if we have any physicists in the playground.

Wikipedia mentions cold plasma, plasma existing at nearly 0 Kelvin. Usually I think of plasma as being hot, like lightning. Can you have plasma at, say, room temperature? Or can it *just* be really hot or really cold (depends on what it's made out of, I suppose, like mercury being liquid at room temperature)?

Suppose you could have plasma at room temperature. Would it dissipate into the air or be more like water where you could set it in a bowl? What would it feel like if you could put it in a bowl? For some reason I picture it as being kind of like... this:
http://www.wizards.com/magic/images/cardart/MRD/Nightmare_Lash.jpg
If hot plasma were to contact water what would happen? Would it evaporate the water? How about if it were to touch wood? Would it set the wood on fire?

Just trying to better understand the fourth phase of matter. Thanks!I believe plasma is defined as ionized gas regardless of the method used to ionize it; while using heat is a method for arriving to it, I believe there are others.

A quick trip to wikipedia mentions the application of electromagnetic fields and the application of electric fields to achieve such a state.

I believe we have room temperature (or around that) plasma; neon lights use plasma and are not considerably hotter than ambient temperature.

I take its reaction with anything at high temperatures would be similar to anything really hot touching something which is not; heat transference. And if the temperature is beyond the flash point, catching on fire of the other object. The plasma would then cool and if it was made plasma through temperature change, slowly revert to a gas as it de-ionizes.

Prime32
2013-07-17, 07:43 PM
I was reading about plasma on wikipedia but was left wanting. I figured I'd see if we have any physicists in the playground.

Wikipedia mentions cold plasma, plasma existing at nearly 0 Kelvin. Usually I think of plasma as being hot, like lightning. Can you have plasma at, say, room temperature? Or can it *just* be really hot or really cold (depends on what it's made out of, I suppose, like mercury being liquid at room temperature)?You can have solids, liquids and gases at room temperature; why couldn't you have plasma? Just because molten metal is hot doesn't mean water is hot.

Suppose you could have plasma at room temperature. Would it dissipate into the air or be more like water where you could set it in a bowl? What would it feel like if you could put it in a bowl? For some reason I picture it as being kind of like... this:
http://www.wizards.com/magic/images/cardart/MRD/Nightmare_Lash.jpgYour question is too general. Plasma mostly functions like a gas; a gas will dissipate, but you could pour it into a bowl if it's heavier than air.

If hot plasma were to contact water what would happen? Would it evaporate the water? How about if it were to touch wood? Would it set the wood on fire?The same as if any hot thing touched it; being plasma doesn't change how its heat works. And some fire is plasma.

Don Julio Anejo
2013-07-18, 01:07 AM

1. Plasma is always a gas, by definition. This is because metal (a solid) can already be considered ionized in a way, as electrons can flow freely from the effect of magnetic fields or the like, although it can't actually store charge (the electrons must flow somewhere, so it functions more like a pipe than a bucket), while everything else can't be ionized.

2. It can exist at pretty much any temperature

3. Fluorescent lights are a perfect example of cold plasma: a stream of electrons passes through neon/argon, causing the gas to first, catch the electrons and aquire a negative charge (hence becoming plasma), and then, emit them (a (-) charged inert gas is extremely unstable since it has a complete valence shell) along with light in the visible spectrum.

4. What we see as fire is always plasma, by definition. In many cases it gives off light for the reason similar to #3.

This is oversimplified and I'm not an expert (I'm more a biochemistry than physical chemistry type), but should give you a decent idea.

faircoin
2013-07-18, 04:26 AM
I don't do plasma. My thesis was on condensed matter fields, and that was a while back (I work hedge funds now... forgot a lot of basics).

Structured systems (most gas, solid, liquid) have binding energies larger than ambient thermal energy. If ambient thermal energy > binding energy, structured systems have their constituents (molecules, atomic collections, etc) disassociate. When the atoms begin to disassociate, you get + ions and - electrons, which still influencing one another, exhibiting high complexity (Kolmogorov complexity, not computational complexity).

Complexity in plasma is an aggregate of dynamical systems. Oak Ridge Nat'l Lab has a fairly accessible (with Wiki cross checking and undegrad education) powerpoint on this subject. http://ddays2008.org/doc/del-Castillo-Negrete-DDays2008.pdf

Most terrestrial plasma start with gases. Why? Thermal decomposition breaks interatomic bonds before ionizing the atoms. Plasma is sometimes (not usefully in more advanced fields) defined as gas which exhibits certain behaviors post-ionization. Quasi-neutral plasma occurs when neutral gasses ionize. They're called quasi-neutral because, a la chaos theory, big things happen with small deviations from ionizing neutral gasses. Non-neutral plasma really occur only in lab experiments, with rotating charged fluids in magnetic fields.

Terrestrial plasmas occur in lightning, fluorescent lamps, glow discharge in micro-circuit fabrication.

Not all plasma is gas! Solid state materials have electromagnetic effects which are plasma, i.e., Alfven waves in liquid mercury. (Lundquist, 1949.)

A popular example of cold plasma would be northern lights. Radiation ionizing them atmospheres, man.

Fire can be plasma, but remember, one defining quality for plasma is high complexity which results from dynamical systems a la ionization. Fire does not have that.

edit

Also, ಠ_ಠ my old plasma textbook used Wikipedia common license pictures in it, I just realized. Lazy editors.

Don Julio Anejo
2013-07-18, 04:37 AM
Huh, live and learn :smallsmile:

How do you define "high complexity" in the context of plasma? Sorry, my physics knowledge is limited to first year university and whatever I've randomly picked up.

faircoin
2013-07-18, 05:34 AM
I switched definitions of complexity throughout the post, which is sloppy work on my part.

The final use of complexity refers to neither Kolmogorov nor computational complexity. It can be better replaced with the term "vigorousness", perhaps.

The meanings of complexity might have stayed the same if I had said "the high Kolmogorov complexity of the dynamical systems" as opposed to "which results from".