Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

This question on Scifi.se: Why does warp plasma burn green? mentions a fictional type of plasma called 'Warp Plasma' that is capable of igniting and when it does it sprays plasma flames/gas out of pipes as if it were oil or some other form of fuel.

Wikipedia says that the sun consists of hot plasma interwoven with magnetic fields. I couldn't find anything about plasma ignition (This is what I originally thought might be a reason why stars are so bright).

Is plasma capable of igniting?

share|improve this question
2  
Yes plasma can! Every four strokes per cylinder of any gasoline engine a tiny plasma thread (called spark) ignites the fuel in the cylinder . –  Georg Nov 18 '11 at 20:15
4  
For clarity, Georg is twisting around your wording to say that plasma can ignite other things, not that plasma can itself be ignited. :) –  endolith Nov 18 '11 at 22:53
add comment

5 Answers

up vote 3 down vote accepted

So in short plasma does not burn green in a chemical sense.

It can rather be quite colorful as can be seen in this picture from the remains of a supernova explosion:

Tycho's supernova from wikipedia

If you have an oxygen plasma for example this can be used to "burn" organic compounds as is often used in the semiconductor industry to clean wafers. The plasma in this case is already at such high energies that it will immediately react with anything that can be oxidized. So you cannot ignite it even further, it is already quite reactive.

If the plasma itself should burn we have to define burning differently. Instead of a chemical reaction nuclear reactions are also possible. To ignite such a nuclear reaction in a plasma you need quite special conditions that exist for example in the sun. These processes are quite different from a chemical burning though and involve reactions at much higher energies.

share|improve this answer
    
Are you sure the pic has not been computer treated: ie false colors ? –  Shaktyai Aug 13 '12 at 6:32
    
@Shaktyai: I did not find a source that states exactly which treatment this image has been going through. In other images, e.g. from NASA only a camera in the visual range was used and they do not state any further image processing: hubblesite.org/newscenter/archive/releases/2007/10/image/a –  Alexander Aug 13 '12 at 13:11
    
One of my teachers in university once showed me this picture, stating the colors were false. As it is very often the case in astronomical images anyway... –  MrBrody Oct 14 '12 at 21:46
    
@MrBrody: I searched around on the Hubble sites a bit but could not find the source of this image. It seems to me at the moment that more than just the optical spectrum is incorporated in the image. In other imagine though, using only the optical spectrum reveals bright colors: chandra.harvard.edu/photo/2012/pne –  Alexander Oct 14 '12 at 23:21
add comment

Plasma is a kind of matter very similar to gas in which atoms have been ionized. It is very hot and lets off radiation (also in the visible spectrum) due to recombination so it might already be considered flame. Thus it isn't clear what "igniting plasma" really means.

In cold plasma where only a small fraction (few percent) of atoms have been ionized you can have normal chemical reactions (aided by plasma's high temperature). Example of such a process occurs in plasma created by lightening and produces ozone (O3). Thus mixing in the right chemicals can result in oxidation occurring within plasma which could be considered burning. For example plasma made up of element which easily oxidizes could be affected by mixing in gas oxygen. I guess it could be considered ignition, but it seems a stretch relative to the ordinary meaning of the word since even cold plasma is already very hot (few thousands degrees Celsius) and causing oxidation to occur inside such plasma would not add a lot of heat (in relative terms).

As for the color, careful engineering can produce plasma where recombination energy is such that light of a given color is emitted.

share|improve this answer
    
Northen light are the most spectacular green plasma available on earth. –  Shaktyai Aug 13 '12 at 6:31
add comment

Ignition in what sense? Chemical energy is out of the question, because plasma by definition are mostly ions unbound of their electrons, which is needed for chemical binding.

Nuclear fusion ignition, well, that is the whole point behind nuclear fusion research. So if someone finds how to "ignite" plasma, it will revolutionize the world, the inventor will become filthy rich, or, worst case, receive a Nobel prize.

There is an independent group trying to do focus plasma fusion with something that resembles huge spark plugs. I have no idea how likely it is that they will find anything interesting soon.

share|improve this answer
add comment

It is interesting because your question meets the research topic of an active grop of plasma physics researchers: it is called Plasma assisted ignition (PAI) and combustion (PAC).

Two examples.

The radicals mentionned by Alexander (when saying "plasmas are at such high energies...") are chemical species, created by the plasma (example: O atoms in an air - N2:02 - plasma, chops of organic compounds with very big reaction constants in air:hydrocarbon mixtures etc), which are very short lived (very short lifetime, because they react very fast with other species that can be found in the mixture under study), and normaly "could not exist in big relative concentrations" in the mixture without the action of the plasma, or of very high temperatures. These radicals, which need plasma to exist massively in the mixture at room temperature, react very fast, and with very low activation barriers. The activation barrier is for example what prevents coal to burn at room temperature: you have to heat it first, even locally with the flame of a match, so that reagents can consume their kinetic energy to start the reaction process, and the reaction chain that will lead to sustained combustion. With plasmas you no longer need an activation energy, or temperature: thus, while combustion starts after hundreds of microseconds and sometimes milliseconds in the case of successful car engine spark ignition, with a proper high voltage nanosecond discharge you can decrease this delay by one or two orders of magnitude, just because the activation factor is not only heat (like, mostly, in sparks), but the dissemination of radicals at a relatively high concentration, high enough to start the combustion at a much lower temperature, sometimes room temperature - or less.

The other application of plasmas, Plasma assisted combustion, shows up especially in unproper mixtures: lean or over-rich mixtures of gas and air, for example. Without plasma, gas can burn with air within some margin of their relative concentration: say 40-60% (don't remember the correct numbers). With the aid of a small, low-energy plasma you can extend this to much more, like 20-70, again because of all the radicals you create. You can stabilize the flame in the burner, although it would have vanished otherwise.

So, this to say, that indeed, in addition to any nuclear consideration, plasmas do "ignite" reactive mixtures in which they would be created, and not only with the heat produced by spark plugs!

share|improve this answer
add comment

A normal flame is already a plasma (Darpa is currently working on a project (Instant Fire Suppression) to control/manipulate flame by using all the plasma techniques ). Now to get a green flame, you just need to add cupper in it.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.