Talk:Plasma (physics)

Railgun

According to the Wikipedia article on railguns and its corresponding Talk page, a railgun is an example of artificial plasma generation and possibly application. Could this be added to a section (for example, Common artificial plasma or Examples of industrial/commercial plasma)? Occamsrazorwit (talk) 14:44, 2 November 2009 (UTC)

Keep Wikipedia G-Rated

The picture showm on the page is a shame!--205.215.119.34 (talk) 14:14, 10 September 2008 (UTC)

A plasma ball? 64.231.108.31 (talk) 16:37, 5 April 2009 (UTC)

Plasma Screen TVs

Do these types of TVs produce real plasma? how do they stop it from blowing up like a fusion bomb?

It would have to undergo the process of either nuclear fission or nuclear fusion, which would be impossible for a plasma TV, as plasma TVs don't actually use or produce any type of plasma. → JarlaxleArtemis 05:58, Jun 19, 2005 (UTC)

It's my understanding that plasma TVs do use plasmas of noble gases, hence the name. (See e.g. Plasma display.) They certainly do not cause nuclear fission or fusion reactions, which generally require extremely high temperature or pressure. Noble gases are used to avoid unwanted chemical reactions, which can easily occur under more reasonable conditions. Plasmas aren't necessarily all that hot, especially if they occur at low pressure.-- Beland 08:52, 10 July 2005 (UTC)

(??should these.......??)

(??should these broad fields be broken down here or in separate links - and if in separate links, ho so because the naming is broad and fairly arbitrary??) (?? I'd say leave the broad picture here then tree out from here on subpages. e.g. as I did Plasma Sources. RBYII ??) --Anon

Units

The equation shows 'cm' and very large powers of 10. Can somebody revise the equations to show 'm'? Bobblewik  (talk) 11:23, 28 Apr 2005 (UTC)

It's not necessary, as 1 cm = 100 m. → JarlaxleArtemis 06:00, Jun 19, 2005 (UTC)

1 m = 100 cm. And no, it's not necessary. You could write those equations with picometres, terametres, zeptometres or exametres (or worse, gigafeet) if you like. But it's common to use only SI base units in combination with scientific notation. The very purpose of scientific notation is to avoid difficult prefixes, so using them here is pointless and confusing. – Boudewijn 1 July 2005 12:34 (UTC)

Table

I think Iantresman's contribution (Characteristics table, plasma vs gas) is a good idea because it is not always clear why a plasma is special enough to be called a distinct phase of matter, but I am not entirely happy with the content. To begin with, it should be emphasized that all the differences mentioned (except "complex properties") are the result of a single difference, the electrical conductivity. Most of the "complex properties" arise from the presence of multiple species that are distinguished by their electrical charge (and in some cases mass). Finally, the electrical charge provides a means to influence the particle velocities directly, not just through collisions, leading to non-Maxwellian distributions and associated phenomena.

Some specific comments:

Electrical Conductivity

Very low Acts as a dielectric or insulator

Near perfect Supports electric currents that can spark or arc; in space plasmas, they are often called Birkeland currents. Such electric currents enable energy to be transferred 'invisibly' from one plasma region to another.

What is a Birkeland current? Currents do not necessarily transfer energy and energy transfer does not require currents.

Duality

None

Yes: passive and active plasmas As soon as an electric current passes through a passive plasma, it becomes active and exhibits more complicated features. In magnetohydrodynamics (MHD), it is practical to ignore the current (representing it as curl B); but as Nobel prize-winner for his work in MHD, Hannes Alfven, points out: "this method is unacceptable in the treatment of a number of [plasma] phenomena .. which require that the electric current is taken account of explicitly" (his emphasis).

Is this standard terminology (in astrophysics)? "Duality" is misleading. What, exactly, was Alfvén talking about?

Complex properties

None

Active plasmas may also exhibit: Noise (i.e., oscillations within a large frequency band) Non-Maxwellian energy distribution (i.e., not smooth) An electron temperature orders of magnitude greater than the ion temperature, which may be much higher than the neutral gas temperature At large current densities, may contract into filaments, sometimes called magnetic ropes or plasma cables, (as seen in lightning, aurora and nebulae) Can separate component gas mixtures in partially ionized gases Can produce double layers, the boundary between adjacent plasmas regions with different physical characteristics, that can explode, facilitate charge separation, and accelerate ions and produce synchotron radiation (such as x-rays and gamma rays) Can produce instabilities, which are identified by their distinct morphology (shape)

A smooth velocity distribution can also be non-Maxwellian. What does "separate component gas mixtures" mean? How can a double layer explode? A double layer does not facilitate charge separation, it is charge separation. What is meant by the "shape" of an instability? The Rayleigh-Taylor instability also exists in neutral gases.

There are a number of minor problems with the content and formulation as well. This table is a good start, but I think it needs a lot of work. Before I start it would help to have some answers to the questions above. Art Carlson 07:59, 2005 Jun 9 (UTC)

Ian Tresman writes:

I was a little surprised to find that someone had removed the table in its entirety, rather than simply moving it to another location.

You have some good questions, and thanks for pointing out my lack of understanding of non-Maxwellian, etc. I wonder whether some of these definitions should be answered with their own separate entries? I would certainly like to expand on Double Layers, for example. I'll add some clarification too. Ian Tresman 14:40, 2005 Jun 10 (GMT)

I didn't remove the table, I moved it to its own section (while editing it substantially).

• Duality: In the wave-particle duality there are two equal aspects of quantum behavior that must both be taken into account to understand some phenomena. In contrast, if you have a model that describes a plasma with current, then you can use also use it to describe a plasma without current simply by setting j = 0. Besides, current is not the real issue. There are many phenomena involving currents that can be described perfectly well within MHD.
• Non-Maxwellian: "Uneven" isn't any more helpful than "not smooth". Why not just "non-Maxwellian" with a link to Maxwell-Boltzmann distribution?
• Double layers: Do you really need a current to produce a double layer? Won't you get a double layer at any boundary between two plasmas with different temperatures? A separate entry for this topic is probably a good idea.
• Instabilities: Like I said, neutral gases also show a number of instabilities (Rayleigh-Taylor instability, Kelvin-Helmholtz instability, Baroclinic instability), so this is not a distinguishing characteristic.

Art Carlson 13:02, 2005 Jun 11 (UTC)

Thanks for your input:

• I don't want to compare plasmas to wave-particle duality, but to the fact that plasmas exhibit a wave aspect (that can be modelled with MHD), and a particle aspect (when an electric current passes through it, and MHD fails.) Sure, the electric current can be neglected in many models (especially when dealing with MHD and waves). But as soon as you get for example filamentation and double layers, then the electric current must be taken explicitly into account.

That sounds likes what I would call a fluid description as opposed to a kinetic description. Let's leave quantum mechanics out of it. For the third time, MHD does not automatically fail when current is present. Art Carlson 12:05, 2005 Jun 12 (UTC)

• We could link 'non-Maxwellian' to the Maxwell-Boltzmann distribution page, but it would be nice to express in a word or two, what this really means. In other words, how is it significant and what does it mean.

• True, double layers do not require a current, and are produced between any adjacent plasma regions with different properites.

Then what makes them explode? Art Carlson 12:05, 2005 Jun 12 (UTC)

• Plasma instabilities formed when an electric current flows through them can have their own characteristics. For example, fluids can produce a Kelvin-Helmholtz instability including plasmas; but pass an electic current through a plasma, and it can produce a diocotron instability which looks remarkably like a Kelvin-Helmholtz instability, but is produced in a different way and has unique characteristics.

Of course a plasma has different and more instabilities than a gas. But that fact would not normally be enough to classify it as a new phase of matter. Art Carlson 12:05, 2005 Jun 12 (UTC)

• If you want to have a go at tidying up the table/page, please go ahead. I can provide you with some addition information if you want to contact me by email, details at Ian Tresman 22:20, 2005 Jun 11 (GMT)

Please correct the Table "plasma scaling" "Density in particles per cubic metre" for "Terrestrial plasmas". In gases you already reach 10^19 particles per cubic cm what is 10^25 particles per cubic metre. The fusion plasma should reach an even higher density.

Complex Plasma Phenomena

I object.

• I have never heard the terms passive and active plasma applied to plasmas without and with current, and I can't find that use with Google. Can you back it up?

Alvén uses the terms in his book, Cosmic Plasma (p.37, 1981) when describing different kinds of plasma regions. Ian Tresman 00:50, 2005 Jun 24 (GMT)

I still don't think the term is either common or particularly helpful. Art Carlson 08:09, 2005 Jun 24 (UTC)

• The phenomena mentioned (Filamentation, Double layers, Birkeland currents, and Circuits) can all be described perfectly well with MHD.

My understanding is that MHD approximates these phenomena, and can misrepresent the particle aspect of the current. One again, this is from Cosmic Plasma. I believe Hall MHD is required for some conditions. Ian Tresman 00:50, 2005 Jun 24 (GMT)

Then you have to specify just what aspect is misrepresented. It's misleading or wrong as it is written. The place to discuss the limitations of a fluid theory is the section on "Mathematical descriptions". Art Carlson 08:09, 2005 Jun 24 (UTC)

• One of them (Double layers) doesn't have anything at all to do with current.

My understanding again is that double layers accelerates ions, hence there is a current? Ian Tresman 00:50, 2005 Jun 24 (GMT)

Not necessarily. It depends on what the electrons and the other ions are doing. An even so, it would be the double layer causing the current, not the current causing the double layer. Art Carlson 08:09, 2005 Jun 24 (UTC)

There may be a point worth making here, but I don't understand what it is, and the section as it stands is unacceptable. Art Carlson 20:37, 2005 Jun 23 (UTC)

If you contact me by email, I'll provide some more information. Ian Tresman 00:50, 2005 Jun 24 (GMT)

Don't you think the info would be useful to all editors of this page? Besides, you can email me here, but you haven't entered your address. Art Carlson 08:09, 2005 Jun 24 (UTC)

I can live with the version of 10:46, 2005 Jun 24, since you've sidestepped the issues of current and MHD. As a physicist I tend to start with equations of state and waves and linear instabilities, but the real world is non-linear, and it is worth pointing out the complex structures that plasmas can form. It may be that what you are trying to express is not kinetic effects as such but non-linear effects, which in many cases come from kinetics. Art Carlson 10:37, 2005 Jun 24 (UTC)

Crystalline non-neutral plasma

I think the phrase "Crystalline non-neutral plasma" in the plasma scaling table needs to be explained more. I'm at least moderately familliar with plasmas and science in general but I find the idea of a crystalline plasma nearly impossible to conceptualize. what IS it?? --Deglr6328 04:16, 5 September 2005 (UTC)

There's not much on the Web about it, is there? To begin with, "plasma crystal" can refer to an ordered array of macroscopic particles in a dusty plasma. These plasmas are neither non-neutral nor cold. That's not what is being refered to here. "Non-neutral plasmas" have just one species, usually electrons. They need to have a good confinement device, such as a Penning trap, and even then they can't contain very many particles before the electrostatic repulsion blows them apart. They have been studied for twenty some years, and the physics is fascinating, if academic. Since there is no recombination with a single species, the temperature can be reduced dramatically. Eventually the Coulomb force between neighbors forces a regular ordering - a crystal. Still, plasma phenomena like plasma oscillations and electric field screening exist. I hope that helps clear your head. Unfortunately, I don't think I know enough to write more than a stub about any of this. --Art Carlson 15:51, 16 September 2005 (UTC)

It does! I think. So, a cold trapped electron (or proton, I guess) cloud basically then? How do you cool an electron cloud though?!--Deglr6328 03:31, 29 September 2005 (UTC)

Not sure, but I think you could let a few cold gas atoms wander around. As long as the electrons are warm, they will lose energy by exciting the atoms, which then radiate. Once the electrons are reasonably cold, they will (slowly, because of the mass difference) lose energy through elastic collisons. You might be able to help things along with some cycles of adiabatic compression and expansion. --Art Carlson 08:59, 29 September 2005 (UTC)

99.999...

comprising more than 99% of the visible universe

Over 99.999% of the Solar System by volume is plasma.

Where do these numbers come from? By volume I hold them to be such underestimates that they are practically misleading, i.e. the solar system is actually closer to 99.99999999999999% plasma by volume. But the volume fraction, whether of the solar system or of the universe, is probably not a very meaningful measure for most purposes. (What is the purpose, anyway?) The concept of "visible universe" is also a bit of a weaselly term. Humph! --Art Carlson 14:20, 16 September 2005 (UTC)

It is indeed a weasily term however it's the most that can be said with reasonable validity. Stars are all plasma and all we see are stars but there is other stuff. dark matter seems to comprise about 90% of the universe and we have no idea what it is. Therefore if we reffered to percentage of the universe instead of percentage of the visible universe we'd have to say 10% and we have no clue about the other 90%. As for 99% being misleading, it does say over 99%. With how little we know about dark matter and black holes I'm satisfied with leaving it at 99% (or 99.99%). I'd rather be a little bit less exact then be wrong. If we say more than 99.9999999999999% and it ends up being 99.992% we could end up looking a little silly. Vicarious 00:05, 21 September 2005 (UTC)

Whether the numbers are 99.992% 99.99999999999999% or 99.999% these numbers are all more than 99%, leaving out dark matter if you will. It clearly states, "comprising More than 99% of the visible universe"....

I think a better way to phrase it to say of visible matter. Within the visible universe we assume (currently) that there is a lot of dark matter. —Preceding unsigned comment added by 209.6.125.212 (talk) 01:30, 12 September 2007 (UTC)

Some estimates suggest that up to 99% of matter in the entire visible universe is plasma. has always been a dorky sentence. I boldly tried to find a better formulation (including some changes in the footnote). Tell me what you think of it. --Art Carlson 08:44, 13 September 2007 (UTC)

Phases of matter

Are there any terms for change of state to/from plasma. For example solid to liquid is melting, gas to liquid is condensation. Is there a term for plasma to gas or anything else related to plasma? Vicarious 00:05, 21 September 2005 (UTC)

I usually say "the gas ionizes" and "the plasma recombines". Also "In semiconductor processing, ignition is the process of starting up a plasma generator." --Art Carlson 07:31, 21 September 2005 (UTC)

Sounds good to me, thanks. Follow up question, is it only possible to go to plasma from gas? It's undoubtedly the primary method but chemistry is full of exceptions. For example theres a term for sublimation when a solid goes to a gas skipping over liquid. My question is, is there a term for anything besides to/from gas, and if not is it not actually possible, or would it simply be referred to as ionizes even if it was solid to plasma?

Image: Large Helical Device

This image was just removed and then revered to return it. It was removed because the nearly 1mb file is too much for dial-up. I'm inclined to agree, especially because it's better suited in the Large Helical Device article then it is here and doesn't do much to clarify plasma in my mind. I'm gonna take it down and add a link to it.Vicarious 17:44, 22 September 2005 (UTC)

I think this image should be kept. It is the only image which strikingly demonstrates the effects of strong magnetic fields on a plasma (you can SEE it twisting) and also wiki is not intended to be designed around the needs of dialup users. There are many pages with animations far larger than this one.In any case the text loads before images so dialup users should not have a problem there anyway.--Deglr6328 23:51, 27 September 2005 (UTC)

Wikpedia does pander to users with lesser computers. For example Periodic table of elements contains Periodic table (standard) rather than Periodic table (large version), although this is primarily an issue of screen size, not bandwidth it still addresses the same point. I'd encourage you to add a better link then the see also section though, perhaps in an empty image box with a link to the actual image. Also a sentence (possibly a caption to the non image) explaining it's pertinence to plasma. I think it's nifty but it's most nifty on a page for manetic fields or for large helical devices, seing a flash of purple doesn't help me understand plasma without a descriptive caption. Vicarious 00:33, 28 September 2005 (UTC)

I asked at Wikipedia_talk:Image_use_policy#Policy_on_large_animations after reverting, but no response. — Omegatron 13:41, 29 September 2005 (UTC)

I liked something Omegatron mentioned at the policy page, what if we add a still of the animation and in the caption link to the animation, it seems like a good compromise. Vicarious 15:29, 29 September 2005 (UTC)

Agree.--Deglr6328 21:47, 30 September 2005 (UTC)

Added to policy. ··gracefool |☺ 22:23, 30 September 2005 (UTC)

Re "Wikpedia does pander to users with lesser computers" - it's not pandering, it's simply accessibility. Wikipedia aims to be accessible to as many people as possible. For instance, articles are designed to be just as readable for people who turn off images (for whatever reason, whether preference or because they are blind). ··gracefool |☺ 22:07, 30 September 2005 (UTC)

No offense intended, just trying to get the idea accross, your terminology was better then mine. Vicarious 01:45, 1 October 2005 (UTC)

So, um, now that we decided what to do I think this is staring contest part where we wait for each other to make the smaller non animated version and post it. I'd like to be the first to immaturely yell "not it". ;-) Vicarious 01:44, 1 October 2005 (UTC)

Haha. So no one ever did this? — Omegatron 03:29, 22 December 2005 (UTC)

Fire = plasma ?

An edit was recently made to the Fire article removing the statement that it is a form of plasma, edit was annotated: "Flames aren't usually considered plasma; they're commonly not ionized much if at all." (made by Atlant)

If this is true, the candle image here should be removed and perhaps a small note added to the body of the article explaining that fire is sometimes thought of as a plasma but actually isn't. --Bk0 23:11, 14 October 2005 (UTC)

I (a plasma physicist) always thought a flame was a plasma. Now that you mention it, I don't know what the degree of ionization of a flame typically is. I found a couple indications, though, that a flame can conduct electricity and therefore must be a plasma:

• http://www.soteria.com/brown/docs/ehydro/speaker2.htm under "Flame Ionization", and
• http://www.madsci.org/posts/archives/feb98/888372043.Ot.r.html

--Art Carlson 11:11, 15 October 2005 (UTC)

Thank you. --Bk0 17:50, 15 October 2005 (UTC)

I discovered some conflicting information from a NASA FAQ saying that not all flames are plasma, as "To create a plasma takes more energy, and requires a higher temperature than the flame provides. The collisions between atoms need to be energetic enough to kick an electron completely out of the atom."

http://www-spof.gsfc.nasa.gov/Education/FAQs7.html#q97 Author and Curator: Dr. David P. Stern (http://www-spof.gsfc.nasa.gov/Education/wstern.html)

I'm not saying that flames cannot produce plasma, but this article currently states "All fire" is plasma, which could be false if this assessment is correct.

Ldhotsoup (talk) 16:53, 5 February 2010 (UTC)

I'm not a plasma specialist, but my experience tells that hot flames could well be plasma (various CVD methods where significant ionization is required) or could be not (phosphorus reaction with oxygen [1]). Thus I'm going to change statements like "all flames are plasma" Materialscientist (talk) 01:58, 6 February 2010 (UTC)

Requested move

Plasma redirects here, so it would remove the unneccesary clarifier.—jiy (talk) 20:33, 26 November 2005 (UTC)

---

Add *Support or *Oppose followed by an optional one sentence explanation, then sign your vote with ~~~~

• Support—jiy (talk) 20:33, 26 November 2005 (UTC)
• Oppose Blood plasma, Plasma display, Plasma television and Plasma cutter exist on Wikipedia - we probably should have a disambiguation page. DV8 2XL 20:43, 26 November 2005 (UTC)
  • Comment Huh? There is a disambiguation page, see Plasma (disambiguation).—jiy (talk) 20:57, 26 November 2005 (UTC)
    • Comment Since that is the happy case then shouldn't Plasma redirect there and be done with it?
      • Comment No. The Plasma display, Plasma television, and Plasma cutter you listed all refer to the plasma being described in this article, which is some indication that the plasma in the physics sense is the main use of the term. Check out the what links here for plasma for more evidence.—jiy (talk) 21:21, 26 November 2005 (UTC)
        • Comment OK, lose those links they don't have to be involved, however the ones listed on Plasma (disambiguation) still need to be accounted for and other disciplines use the term plasma in other ways than does physics. DV8 2XL 21:35, 26 November 2005 (UTC)
          • They are accounted for. Moving Plasma (physics) to Plasma (which redirects to Plasma (physics) anyways) wouldn't suddenly make Plasma (disambiguation) disappear. If you notice, there is a link to Plasma (disambiguation) at the top of Plasma (physics) so if a user is looking for a different term, they can find it. This is standard practice; for instance, see Tree and Blood.—jiy (talk) 22:42, 26 November 2005 (UTC)
• Support—Wechselstrom 03:23, 27 November 2005 (UTC)
• Oppose (but I would support moving Plasma (disambiguation) to Plasma). — Knowledge Seeker দ 03:55, 27 November 2005 (UTC)
• Oppose Agree with Knowledge Seeker, this should be the disambiguation page. "Plasma" has a long history of usage before it was applied to this phenomenon. Jooler 04:30, 27 November 2005 (UTC)
• Support. History of usage has little to do with it. This meaning is more likely to be used without adjective or other qualification, and many of the links to blood plasma come from redirects from [[serum]]. Gene Nygaard 17:41, 27 November 2005 (UTC)
  • Comment A somewhat POV statement as I suspect there are as many health-care workers that use the term to mean a component of blood, as those that use it in the present sense. DV8 2XL 17:49, 27 November 2005 (UTC)
• Oppose. Plasma should be a disambiguation page. --Bk0 (Talk) 19:39, 27 November 2005 (UTC)
• Comment "Plasma" should point to this page (directly or redirectly) because it is the "primary meaning" (see Disambiguation#Page naming), as evidenced by "What links here". I don't see any difference whether this page is called "Plasma", "Plasma (physics)", or "Plasma physics". The note at the top of the page mentions blood plasma specifically because it is clearly the second most important meaning, so any medical students losing their way can quickly get to where they want to be. --Art Carlson 20:30, 27 November 2005 (UTC)
  • COMMENT plasma (physics) and plasma physics should be two separate articles. 132.205.46.170 23:35, 28 November 2005 (UTC)
• OPPOSE, plasma should be a dab page. Plasma in the physics meaning is not clearly the primary meaning. Talk to a medical doctor for instance (there are more of those than physicists anyways). 132.205.46.170 23:34, 28 November 2005 (UTC)

Agreed. Just recently on my local news broadcast they used the word "plasma" as shorthand for plasma TVs ("Thinking of getting a plasma this Christmas? They aren't all the same...", etc). Visitors searching for "plasma" should first reach a disambig page, rather than this article which they may find bewildering. --Bk0 (Talk) 00:17, 29 November 2005 (UTC)

Just because the standards of your local TV station are so poor is not a justification to mess up an Encylopedia. Why not suggest that they get a fact checker on their staff? Vegaswikian 03:44, 30 November 2005 (UTC)

• Support. Most users who are looking for Plasma will want this article. The DAB pointer addresses the few who arrive here incorrectly. Vegaswikian 03:40, 30 November 2005 (UTC)

Discussion

Add any additional comments

This is all wrong Plasma should be a disambiguation page. Jooler 04:30, 27 November 2005 (UTC)

• This is a courtesy notice that I have suggested that Plasma (disambiguation) be moved back to Plasma. The former was created by a cut-and-paste move from the latter, which was then changed to redirect here. — Knowledge Seeker দ 04:46, 30 November 2005 (UTC)
• This is the page, I was looking for, but Plasma (disambiguation) was helpful in my understanding of what plasma means to other people. More numbers would help ie is low voltage 15 pico volts or 15 volts? The latter in ignatrons, electric arc welding and thyratrons, about 100 volts in florescent tubes including compact florescents, I think. The article is appropiate in most respects, but needs occasional explanations directed to the novice. It is appropriate to use both prefixes and powers of ten. Understanding of the latter is decreasing now that slide rules are obsolete. Most dictionaries do not specify powers of ten as a meaning of orders of magnetude = OOM. In my opinion OOM is inappropriate unless the power of what is specified, as astronomers do for the brightness of stars. For star brightness, 6 orders of magnetude = a brightness change of 100 times not one million times. Neil Ccpoodle 22:59, 4 April 2007 (UTC)

Ionized

"Ionized" in this case means that at least one electron has been removed from a significant fraction of the molecules.

Makes it sound like the plasma is a group of positively charged molecules with the electrons removed from the plasma as a whole. Does the plasma have a positive charge or are the electrons floating around in there, too?

The electric arc in an arc lamp or an arc welder

The arc itself isn't plasma, is it? The arc is creating and travelling through the plasma. Likewise with other examples. — Omegatron 01:50, 8 December 2005 (UTC)

Perhaps "dissociated" is a better word re: the electrons? A diagram could help, too. --Bk0 (Talk) 02:24, 8 December 2005 (UTC)

Plasma engines

With the recent sucessful tests by the ESA on plasma engines [2], should a page be made for them? Oberiko 13:47, 15 December 2005 (UTC)

Page moves

I am posting here because I noticed that this page appeared to be a partially completed page move request. Currently, Plasma (physics) redirects to Plasma, but Talk:Plasma (physics) does not redirect to Talk:Plasma. There is also the issue of Plasma (disambiguation) being moved to Plasma. When consensus has been reached on what should be done regarding these articles, please let me know, and I will be more than happy to complete the move request. I am cross-posting this to Talk:Plasma (disambiguation) as I am unsure which set of articles are being actively monitored. Thank you! --HappyCamper 21:07, 25 December 2005 (UTC)

Thanks for your comment, HappyCamper. As one who has been active in the discussions, I am not a disinterested editor, but here is my interpretation of a slightly complex situation:

• On May 3, 2005, a user (without discussion?) copied-and-pasted Plasma (a disambiguation page) to Plasma (disambiguation), then changed the former to redirect to Plasma (physics). The new disambiguation page now has a history as well.
• On November 26, 2005, a user noticed the redirect from Plasma to Plasma (physics) and proposed the later be moved to the former. Again I am not unbiased, but with four votes supporting the move and five against (including an anonymous voter), the requested move clearly did not achieve consensus.
• On November 30, 2005, I proposed moving Plasma (disambiguation) to Plasma. I soon discovered the cut-and-paste move and amended my request. Notices were placed on Talk:Plasma (disambiguation), Talk:Plasma (which had not been moved during the May 3 cut-and-paste), and here on Talk:Plasma (physics) as well.
• The move I proposed to undo the cut-and-paste received two supports (aside from me) and no opposition.
• Today, an administrator, perhaps unaware of the active move requests, deleted Plasma (with 119 edits) without comment. He then moved Plasma (physics) there (leaving the talk page behind), and again left no explanation.
• I saw your comments, discovered the out-of-process actions, and undid both the move and undeleted Plasma.

My summary would be that the proposed move from Plasma (physics) to Plasma failed to achieve consensus. The proposed move from Plasma (disambiguation) to Plasma did, although there was a low turnout, especially as it was performed without discussion. Obviously, I feel that Plasma (disambiguation) should be moved back to Plasma, but I will leave the interpretation up to you. If you decide to do so, you will have to merge the histories, since the current disambiguation page was created by cut-and-paste. Thank you. — Knowledge Seeker দ 23:38, 25 December 2005 (UTC)

Well, I did my best :-) Both the article history and the talk pages needed to be fixed. That was quite tricky! I am going to remove the move request now. --HappyCamper 21:32, 26 December 2005 (UTC)

?!

What is going on here?! In case you haven't noticed, virtually the entire article is now missing! I will revert all recent edits to the dec. 24 version if the above parties involved in recent moves don't fix it.--Deglr6328 07:18, 27 December 2005 (UTC)

Sorry about that—I don't know what happened there. A user had cut-and-pasted one of the articles which made things a bit complex, although I'm not sure how that affected this article. In any case, I reverted the last edit which seems to have fixed matters. Please let me know if I'm correct or fix it if you can. Thanks! — Knowledge Seeker দ 07:46, 27 December 2005 (UTC)

looks ok now.--Deglr6328 08:34, 27 December 2005 (UTC)

Plasma /beta parameter

The 'DIII-D (fusion reactor)' article refers to 'plasma \beta parameter', and this reference is wikified to 'Plasma (physics). However, I cannot see a 'Plasma \beta parameter' in this article.

Please clarify to what the 'DIII-D (fusion reactor)' could be referring to.

Duncan.france 22:44, 16 January 2006 (UTC)

OK. I think I have found it : 'thermal/magnetic energy ratio'. Is that right?

If so, perhaps the 'DIII-D (fusion reactor)' article should be modified accordingly...

Yeah, that's it, but you do call it \beta. In the context of a tokamak device, \beta is the "quality" of the magnetic confinement. The full equation would be roughly (3/2)nkT / (1/2 \mu_0 B^2), which is the thermal energy of the plasma divided by the energy contained in the magnetic field. The value is typically a few percent.

The link should probably point to tokamak, because the DIII-D is/was a tokamak. - mako 05:06, 17 January 2006 (UTC)

Electromagnetic vs gravitational forces

My mistake over EM always dominating gravitation forces for charged particles in a plasma. I think I'm trying to explain the statement in "Dynamics" at Dusty plasmas. --Iantresman 23:15, 21 March 2006 (UTC)

Fundamental plasma parameters

I'm wondering whether the Fundamental plasma parameters should be removed to an article of their own. I must admit that they mean very little to me, and I think that an article of its own would allow room to explain what each one means? --Iantresman 09:45, 24 March 2006 (UTC)

You're right that this section is more technical than the rest — probably too much for the average reader. The reason they are not all explained now is not because of space limitations but because no one has had the knowledge, time and willingness to expand them. The article is already very long, so I wouldn't object if you moved that section to its own page. --Art Carlson 10:36, 24 March 2006 (UTC)

Double layers and synchrotron radiation

I notice that the information on double layers producing synchrotron radiation has been removed. References seem to support that double layers will accelerate electrons through pinches that will indeed produce synchrotron radiation:

• "A very interesting astrophysical application of double layers which was discussed was in connection with extragalactic jets. It was shown that strong plasma double layers can exist within self-maintained density cavities. These double layers will emit relativistic electrons which, in turn, will produce synchrotron radiation making the plasmas in the immediate locality radio luminous." [3]
• "Where double layers form in the pinches, strong electric fields can accelerate the charged particles to high energies, including gamma ray energies (Alfven, 1981). These should then display the characteristics of relativistic charged particle beams in laboratory surroundings, for example, the production of microwaves, synchrotron radiation, and non-linear behavior such as periodicities and 'flickering.'" [4]
• "Double layers produce beams of electrons and, on astrophysical scales, these beams are relativistic. The beams are also directed along Bo so that the expected loss mechanism for the beam kinetic energy is synchrotron radiation." Anthony L. Peratt, Physics of the Plasma Universe (1992)
• "An acceleration mechanism that was first advanced to account for astrophysical phenomena (mainly, acceleration of cosmic ray particles and relativistic electrons in synchrotron jets), is briefly reviewed, and it is shown that a similar mechanism can account for acceleration in the plasma focus. In the plasma focus, current flows through annular channels are defined by radial double layers. " [5]
• "When electrons conducting the currents outside the double layer reach the double layer, they are accelerated to very high energies. Similarly, ions reaching the double layer on their outward motion from the central galaxy, will be accelerated outwards when passing the double layers. The strong axial current produces a magnetic field, which pinches the plasma, confining it to a cylinder close to the axis. Although the electrons are primarily accelerated in the direction of the magnetic field, they will be scattered by magnetic inhomogeneities and spiral in such a way that they emit synchrotron radiation", Hannes Alfvén, Cosmic Plasma (1981).

--Iantresman 12:03, 30 March 2006 (UTC)

I removed that, because double layers produce beams of charged particles and inside the DL there is "linear acceleration emission". The production of synchrotron radiation has nothing specifically to do with DLs. Any accelerated partice in a magnetic field, even a homogeneous magnetic field, will usually have a component of its velocity perpendicular to the magnetic field and will therefore rotate around it. It will emit cyclotron radiation in case the particle velocity is not relativistic and it will emit synchrotron radiation if it has been accelerated to relativistic velocities. It is nice what alven writes, but there is no reason not to assume that the electrons and ions already spiral around the magnetic field before entering a DL. Peratt quote is very misleading, because if the beams are purely directed along B0 then there will be no synchrotron radiation. He is very poorly expressing himself.--Tusenfem 08:48, 31 March 2006 (UTC)

So are we suggesting that the double layer itself does not produce the synchrotron radiation, that there are no plasma-related mechanisms that produce synchrotron radiation, or that some other aspect of plasma may produce synchrotron radiation (eg. double layer accelerated electrons moving through a pinch)? --Iantresman 09:57, 31 March 2006 (UTC)

Well, I am suggesting that (i.e. the first thingy), dunno who the "we" is. A double layer is just a means to get accelerated electrons and ions. The charged particles are accelerated along the electric field. Now, it may be possible that they gyrate around the magnetic field, and they will emit cyclotron/synchrotron radiation. Take a look at a general physics book, for goodness sake, and look up synchrotron radiation. It is created by relativistic charged particles taht gyrate around a magnetic field. From Rybicky and Lightmann "radiation processes in astrophysics" (one of the best books I think on this topic) chapter 6: [i]Particles accelerated by a magnetic field B will radiate. For non-relativistic velocities the complete nature of the radiation is reather simple and is called[/i] [b]cyclotron radiation.[/b] [i]The frequency of emission is simply the frequency of gyration in the magnetic field. However, for extreme relativistic particles the frequency spectrum is much more complex and can extend to many times the gyration frequency. This radiation is called[/i] [b]synchrotron radiation.[/b]. All one needs is a relativistic particle in a B field to get synchrotron radiation. A DL can be the cause that there are relativistic particles. It is A creates B and B creates C, but that does not mean that A creates C. Only relativistic DLs will create relativistic particles which can create synchrotron radiation. Any other DL will not. --Tusenfem 12:02, 31 March 2006 (UTC)

Temperature

The defining characteristic of a plasma is ionization. Although ionization can be caused by UV radiation, energetic particles, or strong electric fields (processes that tend to result in a non-Maxwellian electron distribution function), it is more commonly caused by heating the electrons in such a way that they are close to thermal equilibrium so the electron temperature is relatively well-defined. Because the large mass of the ions relative to the electrons hinders energy transfer, it is possible for the ion temperature to be very different from (usually lower than) the electron temperature.

I see a problem here in the first few sentences. First it is said that the ionization can be caused by ... but more commonly caused by heating. I think the sentence stop there. What comes behind has noting to do with ionization, there the paragraph enters into the temperature domain. One does not just heat the electrons, one heats the whole gas, which in the end, because of collisions etc. will give electrons enough energy to escape the nucleus. For the temperature, there is exchange of energy between the electons and between the ions, but not inbetwixt because of the greater mass of the ions. To thermal equilibrium is reached by the electrons and by the ions at different tempreratures.--Tusenfem 12:55, 4 April 2006 (UTC)

If only a small fraction of the gas molecules are ionized (for example 1%), then the plasma is said to be a cold plasma, even though the electron temperature is typically several thousand degrees.

Unfortunately, this is wrong. A plasma is not called cold because it has a low ionization degree, but when each species has only one energy, i.e. all electrons have one velocity and all ions have one velocity, there is no spread in velocity space. Naturally, this means that also the definition of a hot plasma is wrong.--Tusenfem 12:58, 4 April 2006 (UTC)

Because the plasmas utilized in plasma technology are typically cold, they are sometimes called technological plasmas. They are often created by using a very high electric field to accelerate electrons, which then ionize the atoms. The electric field is either capacitively or inductively coupled into the gas by means of a plasma source, e.g. microwaves. Common applications of cold plasmas include plasma-enhanced chemical vapor deposition, plasma ion doping, and reactive ion etching.

This needs to be rewritten, as it is not very clear. a microwave is not a plasma source, but is used in a plasma source. Also, again the cold thing here, it may be correct that 'technological plasmas' are cold, I don't know, it is not my field of expertise. And the electric field being capacitively or inductively coupled to the gas does not make sense. Inductively you would create a current with a magnetic field. I hope someone with expertise in technological plasmas can change this.--Tusenfem 13:05, 4 April 2006 (UTC)

Can you come up with a better definition for cold and hot plasmas, that people will understand. I think I also read somewhere that the electrons in a cold plasma do not have enough energy to move out of the ions's debye sphere, and that a low ionoized gas typified a cold plasma? --Iantresman 14:17, 7 April 2006 (UTC)

The definition of a cold plasma is that the electrons (ions) have a very small temperature spread. A temperature is given by a distribution function that peaks at a certain temperature, comparable with a Gaussian distribution. Now, imagine that in this Gaussian distribution the width goes to zero. Then you get a delta function, all electrons (ions) have the same "temperature". Naturally, a temperature is a moment of the particle distribution function, so what this means is that all electrond (ions) move with the same velocity.

So definition: A cold plasma is a plasma in which all electrons (ions) basically move with the same velocity, there is no spread. In physical terms, this means that the particle distribution function can be seen as a delta function in velocity space. Contrary to expectations, a cold plasma can have a very high temperature, assuming that the temperature is given by $T_{e,i}=0.5 m_{e,i} v_{e,i}^2/k_{Boltzmann}$.

I have never seen the definition that you wrote down about electrons not being able to move out of the ion's DeBye sphere. Through Saha's equation you can see that low temperature plasmas will have a smaller ionization grade. But low-temperature cannot be set equal to cold, in plasma physical terms.

Naturally, I am willing to rewrite the section about temperature. Cheers, Martin --Tusenfem 16:49, 8 April 2006 (UTC)

That explanation is very confused. Electrons have a distribution of velocities, not of temperatures. The temperature (if it is definable at all) is found from the width (spread) of the velocity distribution. It is possible, but practically never the case, that the mean electron velocity is greater than the thermal velocity. These things may muddy the water, but they are not the problem here. Obviously a plamsa with T = 0 is cold; the question is, how warm can a plasma be and still be considered cold? The answer I gave, and to which I stand, is that the biggest change is properties as a plasma goes from very cold to very hot, is when the degree of ionization approaches unity. This makes double sense because the Saha equation tells us that the ionization depends sensitively on the temperature and hardly on anything else.

I can't make any sense out of the Debye sphere business.

I do not like the section "Types of plasma" at all. They are not "types", the section mixes categories that have little in common, and most of the topics belong more naturally in a different section.

--Art Carlson 08:41, 9 April 2006 (UTC)

Art! I think that is what I wrote, that the electrons have a spread in velocity. In plasma physics you will find the so called cold-plasma approach, in which it is assumed that all electrons or ions have the same "temperature", meaning that there is no thermal spread in the velocity distribution function, each species is described by charge, mass number density and velocity, and thermal motion is neglected. See e.g. Don Melrose's book Instabilities in space and laboratory plasmas chapter 2.

Naturally, if you like, you can determine cold-warm-hot with respect to temperature, but what sets the limit? Is a plasma cold if it has less the say 1% of ions? AFAIK in my field of research a cold plasma is as defined in the few sentences above. --Tusenfem 11:49, 10 April 2006 (UTC)

I'm sure you think that you wrote that, but it's not what you actually wrote. A single electron does not have a temperature, so it doesn't make any sense to say that "all electrons have the same temperature".

Again, there is no question that a plasma is cold when T=0. The question is how high T can be before you can no longer treat the plasma as if T=0. I insist that a common and useful distinction is the degree of ionization. Do you have a problem with including that in the article?

There can well be other distinctions. For example when considering plasma oscillations, a plasma is "warm" when the spatial scale of the problem is smaller than the Debye length. We could expand the explanation of "warm" and "cold" plasmas in different contexts, but it is not enough to draw the line at T=0.

--Art Carlson 12:43, 10 April 2006 (UTC)

I think that related to this, is that sometimes there are formal and informal definitions, and the latter is often more informative to the non-scientists. For example, I recalled that by formal definition, a plasma is defined by the "plasma approximation" having a certain value? But informally, it is an ionized gas.

So I wonder whether "cold plasma" has formal and informal definitions? I suspect that there is a relationship to the degree of ionization, but it does not define it?

Here are some definitions of cold plasmas that I have found in the literature:

• "The cold plasma model assumes in fact, a zero plasma temperature..." (Fundamentals of Plasma Physics by J A Bittencourt) [6]
• "We assume that there are not any random motions. This idealised system is referred to as a cold plasma. The particle function of a cold plasma is a [delta]-function centred on the average velocity". (An Introduction to Plasma Astrophysics and Magnetohydrodynamics by Marcel Goossens) [7]
• "A cold plasma is one whose particle energies are small enough that electromagnetic forces contrain the plasma to move with the magnetic field' A hot plasma is energetic enough to escape such constraints." (Neptune by Ellis D Miner, Randii R Wessen) [8]
• "By a cold plasma, we mean one in which the electr temperature may be neglected and ion motion is unimportant" (he Solar Corona by Leon Golub, Jay M. Pasachoff) [9]
• "In a cold plasma, where the charge carriers oscillate about fixed positions, T=0 . In a hot plasma, bodily transport of density, velocity, and energy fluctuations by the free-streaming particles lead to finite values for T." (Anthony L . Peratt, Physics of the Plasma Universe)

--Iantresman 13:35, 10 April 2006 (UTC)

Okay, we'll just leave it as it is, although it is fairly common to give an electron a temperature with the relationship I gave above. Just make clear that you use the Saha equation to define cold-warm-hot and try to come up with good values.

I didn't really like the section on temperature as it was: temperature is (roughly) defined in terms of free energy per degree of freedom, and measured in Kelvin and eV, and this is the most important thing to start with. Ionisation is dependent mostly on temperature, sure, but we shouldn't start a section on temperature by talking about ionisation, as the definitions of hot and cold are secondary considerations compared to the meaning of temperature itself. So I have reordered it, and removed some material which could better be placed elsewhere. To fit it in with the flow of the section, I have also added the plasma characteristic, 'Degree of ionization'.

--Dashpool 18:00, 27 April 2006 (UTC)

Could some distinction be made between thermal and nonthermal plasma in this section? --212.108.17.165 10:39, 29 August 2006 (UTC)

Good show, good article!

Contratualations to the editors who have contributed to this article, it seems that we have now acquired "Good article" status. Maybe the article is now on its way towards Featured article status.

I still think there is room for improvement, probably starting with a better categorisation of section. --Iantresman 07:40, 7 April 2006 (UTC)

Types of plasma

I've expanded the section on Ultracold plasma to be one on "types of plasma", since we don't really discuss them together. I wonder whether the section on Common plasma would make a good introduction to this section, and the whole section moved to where Common plasmas is now? The section on Characterists seems a bit more technical, and have lesser appeal, and perhaps should come afterwards? Ideally we should mention some of the characteristics in the section on type, in order to warm the reader to them? --Iantresman 22:29, 7 April 2006 (UTC)

J.J. Thomson

In keeping with the wikipedia suggestion to be bold, I have changed (Sir) Joseph John (J. J.) Thomson, to Sir J. J. Thomson. In my estimation, J. J. Thomson is more well known, and the initials may be found out by following the link. The reason for including Thomson's title the link is it matches the link to Sir William Crookes. Forgive me if this issue has already been dealt with and settled. -Fermion 06:41, 19 April 2006 (UTC)

plasma parameter

1. Shouldn't the number of particles in a Debye sphere be (4pi/3)*n*lambda_D^3 (instead of (4pi)...)?
2. Is there a deeper connection between the use of Lambda to denote the number of particles in a Debye sphere and the use of Lambda to denote the ratio of the maximum to minimum effective impact parameter (as in lambda = ln(Lambda), see Coulomb collision? Or is it just notational double-duty?

--Art Carlson 10:12, 17 May 2006 (UTC)

• I've corrected the Debye sphere calculation, though I'm still not entirely sure what factor "defines" a plasma as a plasma. On the one hand, Λ<<1 is the plasma approximation, but Λ>>1 is a "Weakly coupled plasma".
• The text also says that "This second criterion can be expressed as Λ>>1"; but I'm not sure what is the "first criterion" as three points are shown? --Iantresman 13:08, 22 June 2006 (UTC)

• ...and answering my own question, it refers to the second of three criterion specified. --Iantresman 13:23, 22 June 2006 (UTC)

Deglr6328

Better people than you or I have judged Peratt's work to be worthy of publication in, for example, Astrophysics and Space Science,[10], and The Astronomical Journal,[11]. I suggest that you write them a letter and tell them how nutty you think his work is.[12]

Incidentally, Peratt's book contains nothing about cosmology... hence it's title, Physics of the Plasma Universe. --Iantresman 00:19, 4 July 2006 (UTC)

sorry, not buying it, sell it to someone else. and as long as we're airing grievances, I frequently find your edits to be intellectually dishonest in the extreme. --Deglr6328 00:52, 4 July 2006 (UTC)

It's not for you to buy, or judge; What you or I think of plasma cosmology is not worth a fig. Not that plasma cosmology has anything to do with plasma physics... except perhaps that a plasma cosmologist, Hannes Alfvén has contributed more to astrophysical plasmas than most.

As for intellectual dishonesty, it is ironic that someone who claims to have "little patience for pseudoscience"[13] has to resort to "attacking the motives or character of anyone..", a characteristic found in the section on "Identifying pseudoscience"[14] --Iantresman 09:06, 4 July 2006 (UTC)

Plasma filaments in nebulae

Art, what am I missing regarding plasma filaments in nebulae? I concede there is no proof that nebulae contain filaments due to any specific cause, (ie. they must be theory/hypothesis), etc. But the following all have the characteristics of plasma filaments, and are recognised by the authors as plasma filaments:

• Graham, et al, note that regarding the Crab nebula, "... the current density in the filaments is too low for significant molecule formation.." (last para.)[15].
• Münch on the Crab Nebula notes "... the filaments move in a force-free field, in which the current density j, is parallel to the magnetic field strength,..." (top right column)[16].
• And doesn't Hardee mention in regard to the Crab nebula that "the plasma forms quasi-stationary self-pinched current filaments",[17] not because of a random theory, but because (a) filaments are seen,[18] (b) they can also can explain the infrared, optical, X-ray, and gamma-ray pulsed emissions.

I realise that just having the characteristics of a plasma filament does not make something a plasma filament. But isn't like arguing that just because it has the characteristics of dark matter, it does not make it dark matter because it is not "seen"? --Iantresman 11:16, 4 July 2006 (UTC)

I was perhaps edgy because you twice described phenomena as filaments that are probably shock waves. Besides, not everything has to be filaments; four examples is plenty, particularly if the evidence for filaments is indirect und speculative, as in Hardee. On the other hand, I think Hubble views the Crab Nebula M1 is a rock-solid reference tha some structures in the Crab Nebula are called and are considered to be filaments. I see, no indication that these filaments have anything to do with currents, Birkeland or otherwise, and the wording we choose should reflect that. --Art Carlson 12:17, 4 July 2006 (UTC)

By the way, it sounds like Dickel thinks it's an open question, whether the structures observed in supernova remnants are really (3D) filaments or not. --Art Carlson 12:37, 4 July 2006 (UTC)

I supsect there are views and supporting evidence on both side, and I wouldn't be surprised if both are correct... I don't think they are mutually exclusive. --Iantresman 14:57, 4 July 2006 (UTC)

Plasma parameter

I moved the text and table on the plasma parameter to its own article: trying to avoid getting the reader bogged down in details, but keep the useful writeup. Dashpool 13:21, 8 July 2006 (UTC)

Would it be better to combine the new article with Coulomb collision aka Coulomb logarithm? --Art Carlson 14:00, 8 July 2006 (UTC)

I have no objection to that. However, Coulomb collision as a title sounds very specific: I would have just expected a discussion of the two-body interaction. Dashpool 15:18, 12 July 2006 (UTC)

Peer review

The article has already achieved Good Article status, so I figure that Peer review is the next step for improvement.

Please make comments at Wikipedia:Peer review/Plasma (physics)/archive1 --Iantresman 10:58, 18 August 2006 (UTC)

Plasma shields?

I am an engineering student and I am quite interested in Science Fiction. I have heard mentions of plasma shields in many science fiction films, books and games and I was wondering whether the experts might post something on the article about them. Is there actually a theory behind a plasma 'blast shield' or is it just writers trying to sound cool?

Being science fiction, there is little information on what and how a plasma shield might work. Which isn't to say that scientists haven't thought about a "plasma shield" [19]. But I think this might be better suited to an article of its own, as this is arguably one of the myriad of applications of plasmas. --Iantresman 11:58, 26 September 2006 (UTC)

I think you might be interested in reading the plasma window article. --Art Carlson 12:25, 26 September 2006 (UTC)

I've set-up a redirect from Plasma shield to Plasma window. --Iantresman 12:30, 26 September 2006 (UTC)

i beleive that a plasma shield is simplay a fictional creation created by authors as a piece of fictional equipment. This is because plasma is a higher state of matter thangas, hence it cannot efficiently absorb impacts. It might just combust, or explode. —Preceding unsigned comment added by Polikol22 (talk • contribs) 21:57, 6 November 2010 (UTC)

Experiment

Should something like this be added to the article? An explanation perhaps? http://video.google.com/videoplay?docid=6732382807079775486 --jholdaway 09:42, 18 October 2006 (UTC)

Missing section

This plasma article seems the most appropriate, but a multitude of science fiction has plasma based technologies. Shouldn't there be a "plasma in popular culture" blurb? i kan reed 02:23, 15 November 2006 (UTC)

Plasma modeling

I created a new page on Plasma modeling. I suggest that the mathematical description section in this article be shorter and the details be moved to a new page plasma modeling. --Mindgame123 22:09, 3 December 2006 (UTC)

Popular culture

What's with all those whacko references under "popular culture"? They're obscure, at best. Most are from niche markets, hardly what I'd call mainstream. 129.16.97.227 16:03, 4 July 2007 (UTC)

Fun to make in the microwave?

If no one else noticed, someone should take away "fun to make in the microwave" at the start of the topic. I'm pretty sure it's a pointless joke. I would but I don't have an account. P.S. If I put this in the wrong spot then sorry.

You don't need an account to do this, just follow the instructions. - Saibod 08:12, 21 July 2007 (UTC)

make your own light saber!

if you put one foot on a plasic box and the other on the ground. Put one hand on the ball and the other holding a long plasic rod and turn off da lights. It glows. It's kwl fun for parties. —The preceding unsigned comment was added by OsirisV (talk • contribs) 00:18:25, August 19, 2007 (UTC).

Dark matter edit

I just reverted this edit. I've never seen "phase of matter" refer to anything but baryonic matter. This is clear if you start to talk about the volume fraction of different phases, since dark matter occupies 100% of the volume of the universe, as does dark energy, which should then also be mentioned. The details are explained in the footnote, and I think it's cleaner to leave the whole discussion there. --Art Carlson (talk) 12:07, 20 November 2007 (UTC)

GA Sweeps (Pass)

This article has been reviewed as part of Wikipedia:WikiProject Good articles/Project quality task force. I believe the article currently meets the criteria and should remain listed as a Good article. The article history has been updated to reflect this review. Some areas for improvement follow:

There's some general clean-up that should be done:

• All values should be in the form "number,non-breaking-space,unit" so 20 km would be coded "20 
• All equations should be updated to LaTex style for clarity and consistancy
• A number of new terms where hilighted using boldface—while this does help accessiblilyt to a general reader, "quotes" are prefered for this according to the Manual of Style. I've gone through and changed these where appropriate.

The history section needs the most attention. In highly technical and scientific ariticles, the lead and history sections are most likely to be of general interest, and extreme care should be taken to make them as clear and accessible. See wp:JARGON and [[wp:[edit]Wikipedia:Make technical articles accessible]] for more information.

Re "Common forms" table: Embedded lists with no content are less preferred than prose. Perhaps the commons forms table could be expanded to an "Indented List with content" (see WP:Embedded list for an example)

Definition: In the list of requirements, numbers 2 and 3 should be phrased the same way as number 1. Since all three are requirements, they ought to all start with "something must be something" or similar.

--jwanders^Talk 07:02, 24 February 2008 (UTC)

---

Plasma physics and plasma should be two different articles. If by plasma (physics) it is meant "plasma" itself (which is the way it is understood), we cannot have it at the lower level of "Category:Plasma physics"; it is like putting Category:Astrophysics under either Astronomy article or Physics article.

Sina2 (talk) 17:50, 1 April 2008 (UTC)

Is this intended to mean what it does mean?

"Plasma typically takes the form of neutral gas-like clouds (e.g. stars) or charged ion beams, but may also include dust and grains (called dusty plasmas).[1] They are typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move more freely."

What these two sentences tell me is that the "dust and grains" which are sometimes in plasma are "typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move more freely".

I believe this to be nonsense and not what was intended. The confusion is caused by several facts.

• grammatically, the word "they" must relate to the noun(s) that immediately precede it ie. "dust and grains", not the word "plasmas" which is the subject of the first sentence.
• "dusty plasmas" occur most frequenntly in conjunction with stars, but the word "stars" is bracketed, and therefore a passing example, not related to "dusty plasmas" (grammatically).
• The inclusion of the ""but may also.....etc" is in the wrong place. It disrupts the meaning.

Comment: To the editors of this article, prioritise the information. Don't include any "but alsos" until you have made a clear statement about the subject.

Suggested rewording "Plasma typically takes the form of neutral gas-like clouds (eg. stars) or charged ion beams (eg. lightning). They are typically formed by heating and ionizing a gas, stripping electrons away from atoms, thereby enabling the positive and negative charges to move more freely."

Having removed the reference to dusty plasma, the two sentences now make sense. That "one more fact" can turn a GA into a shamble, or possibly serious misinformtion. (The problem is, that if you know your subject well enough, the misalignment can pass you by.)

• The fact about "dusty plasma" now needs to be reinserted in the appropriate place. Possibly a following sentence such as: '"Some plasmas (is the plural correct?), particularly stellar plasma (is this correct?), may include suspended particles of solid matter and (not "which") are known as "dusty plasma".

NOTE please check for factual accuracy before inserting. Also- not "dust and grains". "Grains of dust" is acceptable, but "dust and grains" implies a windstorm in a wheat-growing area.

Amandajm (talk) 02:53, 19 April 2008 (UTC)

Too technical?

As a layperson in science, I understand the key elements of the article, and believe the level of technicality is necessary. After all, plasma is a technical topic that doesn't need to be understood for everyday life, much like so-called 'rocket science'. Surely therefore, readers of the article will a) have an interest and a sufficient level of scientific knowledge to deal with the topic, or b) only need to read the initial definition to find out what plasma is - fundamentally, a fourth state of matter. —Preceding unsigned comment added by 194.81.36.61 (talk) 11:56, 26 June 2008 (UTC)

Um... What?

"Waves

Since electrons and ions can move independently of each other, we can have plasmons. Plasmons will then mix with photons to give massive polaritons."

Speaking as an uninformed reader, these sentences look a lot like nonsense. What am I missing? I think they should be reworded to be less ambiguous. - Syclamoth

Speaking as an expert in plasma physics, I wasn't able to identify these sentences as nonsense, but I don't understand them either. I also question whether the phenomenon is important enough that it should be included in a survey article. Art Carlson (talk) 10:03, 22 July 2008 (UTC)

Some Comments

Reading through the page, I have a few comments:

I tried to deal with some of these. (AC. "I have other names. If you're interested.") Art Carlson (talk) 14:58, 7 August 2008 (UTC)

In "common plasmas" :
1. Notable plasma physicist Hannes Alfvén also noted that due to their electric charge, very small grains also behave as ions and form part of plasma (see dusty plasmas). Should one not make a comment here that small grains in and of themselves are not charged, they can be charged by interactions with a plasma.

Changed. - AC

2. why is the aurora a plasma? It may be created by charged particles but the light we see is from neutral oxygen and nitrogen that is being excited, not ionized
3. why is the Io-Jupiter flux tube a plasma? It might contain plasma, but it is just a "physical construct" made up from field lines.

In "Degree of ionization":
can have the characteristics of a plasma (i.e. respond to magnetic fields and be highly electrically conductive) However if we look further up what the characteristics are of a plasma in "definition of a plasma" responding to magnetic fields and being highly conductive are not characteristics.

In "temperatures"
Based on the relative temperatures of the electrons, ions and neutrals, plasmas are classified as "thermal" or "non-thermal". I usually define thermal and non-thermal based on the fact whether the distribution function is Maxwellian or non-Maxwellian. But maybe this differs in different plasma disciplines.

I'm inclined to agree with you. Can we find a reference one way or another? - AC

In "waves":
I also do not understand these 2 sentences. But for plasma waves one could easily make a whole separate page.

Nobody does. (See previous section on this talk page.) I'll remove it. - AC

In "filamentation":
The first sentence is not a sentence, it lacks a verb, probably "are seen" instead of "seen"

Fixed. - AC

In "shocks and double layers":
The first sentence is not a sentence, it lacks a logical ending.

Fixed (or at least improved). - AC

In "Electric fields and currents":
Quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits. I fail to see why quasi-neutrality requires this.

Quasineutrality requires that the current be divergence-free. This does not necessarily mean that current loops in any meaningful sense can be identified. I think this is part of the plasma cosmology mindset. I'm a bit afraid to fiddle with this section because I might accidently delete something meaningful but merely unfamiliar. - AC

Sorry but I still don't get this. Quasi-neutrality means that over a large volume compared to the DeBye sphere, the total charge is zero (where there can be deviations within the volume of the DeBye sphere). Now if there would be a current in this plasma J = -ne * ve * e + ni * vi * e, and it would have a finite divergence Div(J) != 0, which basically means that -grad(ne).ve - ne.div(ve) + grad(ni).vi + ni.div(vi) = alpha. There is no reason to assume that this would violate quasi-neutrality. Assuming e.g. no density gradient, this just means that ni.div(vi) = alpha + ne.div(ve). If quasi neutrality holds, i.e. ni = ne this just means that the electron velocity changes in space differently from the ion velocity, which is no problem whatsoever.

And do you mean mainstream plasma cosmology or do you mean electric universe PC? if the latter, I could not care less what their mindset is. --Tusenfem (talk) 11:37, 13 August 2008 (UTC)

Equation of continuity: $\frac{\partial\rho}{\partial t} + \nabla\cdot j = 0$

Where there is a divergence of the current, the charge density will change with time, so quasineutrality cannot be satisfied except momentarily. Art Carlson (talk) 08:34, 14 August 2008 (UTC)

Oops, I stand corrected, sometimes it's the basic equations that one forgets.

Is there any such thing as "mainstream plasma cosmology"? I was just pointing out that one of the editors of this article was an advocate of plasma cosmology, and that might explain some of the content. If that is the case here, then it should be refactored to the conventional view. Art Carlson (talk) 08:45, 14 August 2008 (UTC)

Well plasma physics does play a role in normal cosmology, but the point is moot, I was wrong.

In "common artificial plasmas":
If we want to adhere to SI we should change Torr to Pascal.

Go ahead, if you want, but in practice this is an area where working scientists often deviate from SI units. - AC

Okay, just my 2 eurocents of comments. --Tusenfem (talk) 12:09, 7 August 2008 (UTC)

A question

Does somebody have information about the flammability in the plasma (state of matter)?

Thanks,

--190.67.186.169 (talk) 18:53, 13 August 2008 (UTC)

I don't understand your question. You might say a plasma can't burn because it's already hotter than a flame. Art Carlson (talk) 08:33, 14 August 2008 (UTC)

Shape and Volume

The article says: Plasma does not have a definite shape or a definite volume.

What exactly does this mean? Can't I take an enclosed ball of gas of definite volume, energize it into plasma, and call it "plasma of definite shape and volume?" Ungtss (talk) 12:37, 6 December 2008 (UTC)

A solid object has the same shape and volume whether you put it in a bucket or a vase. A liquid will change its shape to fit its vessel, but keeps its volume. A gas - or plasma - will not only take on the shape of its vessel, it will expand to fill it. That's what the sentence means; whether it is a good sentence to have in the article is another question. --Art Carlson (talk) 16:53, 6 December 2008 (UTC)

Awesome -- thanks for the clarification. I'll fix. Ungtss (talk) 17:07, 6 December 2008 (UTC)

Thanks. That's an improvement. --Art Carlson (talk) 19:43, 6 December 2008 (UTC)

State

I thought plasma was a different state of matter. Isn't saying "In physics and chemistry, plasma is a partially ionized gas" like saying "In physics and chemistry, a liquid is a melted solid"? 75.118.170.35 (talk) 17:39, 30 December 2008 (UTC)

State of matter is not a particularly rigorously defined concept. The idea of this sentence is to give a quick orientation about what a plasma is. I'm a plasma physicist, and I usually think of a plasma as just a gas with a large electrical conductivity. That gets you pretty far. --Art Carlson (talk) 18:58, 30 December 2008 (UTC)

Bit isn't describing it as an ionised gas fairly misleading as plasma exhibits some very different behavior? I used to work in plasma physics and most of what I learned was how plasma is different to ionised gas. Adwol (talk) 11:50, 6 January 2010 (UTC)

Plasma a distinct state of matter. The lede says that plasma is a type of gas. But I believe that the definition precludes it from being a gas. Art, yes, it is true that this is just going off a definition, but the definition isn't so undefined, as you say. Plasma has gas- and liquid-like properties. That's why it is a state of matter distinct from a gas. ask123 (talk) 04:55, 7 February 2010 (UTC)

I just spent some time browsing. In Internet a plasma is sometimes defined as an ionized gas, but sometimes it is emphasized that a plasma is not a gas. The few text books on my shelf don't really settle the question either. The definition I like best is from Chen's Introduction to Plasma Physics:

A plasma is a quasineutral gas of charged and neutral particles which exhibits collective behavior

This might serve as a compromise since the equality "plasma = gas" is somewhat weakened. I think Chen is a good source because it is a commonly used textbook aimed at an undergraduate audience (but still often used in graduate studies), which is about the ideal level for a Wikipedia article on this topic. If you look at the article on State of matter, you will see that "state of matter" is also not so easy to define. It is easier to unambiguously identify states of matter when there is a first-order phase transition. There is no such transition going between a gas and a plasma. One thing I don't like about the new edits is the emphasis on "high energy". It is possible under various circumstances to have a cold plasma. According to the Saha ionization equation, this can even be the case in thermal equilibrium if the density is low enough. There are also a number of statements that don't make sense, like "plasma molecules can flow in a coalesced unit". I will revert the edits because I think the old version is definitely clearer and more accurate, but am willing to help find a different definition that makes everybody happy. --Art Carlson (talk) 10:14, 7 February 2010 (UTC)

I think this is just another case of sloppy language in physics, or perhaps just sloppy language in beginning physics text books. I think my following explanation would be clearer than what's been said so far:

In physics, a plasma is a rather tenuous collection of particles that is ionized to some degree, meaning that some portion of the particles is charged and some portion is neutral. The particles may be fundamental particles and/or composites such as atoms or molecules. Is a plasma a gas? A gas is an equally vaguely defined state of matter, and the relationship between these definitions determines whether a plasma is a gas or not. What is clear is that a plasma is a different state of matter than a gas made of neutral particles, a "neutral gas". If one's definition of "gas" is equivalent to "neutral gas", then a plasma is not a gas. (We could come up with a word for "tenuous collection of particles", and both plasmas and gases would fall into that category.) If one's definition of "gas" accepts "ionized gas" as a subset of gases, then a plasma is a gas, since a plasma could then simply be defined as an ionized gas. (An "ionized gas" could also be called a "quasineutral gas".)

Now, it seems to me that if anyone says "a plasma is an ionized gas", they have stated either 1) that a plasma is a special kind of gas, or 2) a poor definition (analogous to the "liquid is a melted solid" example given above), which can easily be mistaken for statement 1. That causes immense frustration when these same people then go on proclaiming that a plasma is not a gas. --Zeroparallax (talk) 07:15, 5 April 2010 (UTC)

We are really just talking about the lead sentence, aren't we? By the time we get to the third sentence we are already starting to work on the distinctions between plasmas and (other) gases and describe it as a distinct state of matter. For those who read farther, there are complete sections on Definition of a plasma and Comparison of plasma and gas phases. The classical way (not always the best way) to resolve disputes in Wikipedia is to cite authoritative sources. I have offered Chen, and would be willing to use and cite his definition in the lead. Do you have a RS contender? There are other ways we could modify the current definition. Perhaps, "plasma is a gas-like state in which a certain portion of the particles are ionized". Nothing I can think of is as crisp as the current version. Would you like to make a suggestion? Just for the first sentence. I find a number of problems with replacing the lead with your paragraph above. --Art Carlson (talk) 10:13, 5 April 2010 (UTC)

The lead sentence (and whatever definition you use for "plasma", and for "gas" and "liquid", for that matter) is very important. As it stands right now, I'd say the whole first paragraph is made contradictory because of the lead sentence (since the lead sentence says "plasma is a gas" and later in the paragraph it says twice that plasma is "unlike gas".) That kind of confusion could dissuade people from even getting to the later sections that help to clarify but do not resolve the contradiction. Does "RS" mean "respected source"? I looked up a definition in one of my most respected sources (the Oxford English Dictionary) and found a definition that is more broad than I expected:

6. Physics. An ionized gas containing free electrons and positive ions, formed usually at very high temperatures (as in stars and in nuclear fusion experiments) or at low pressures (as in the upper atmosphere and in fluorescent lamps); esp. such a gas which is electrically neutral and exhibits certain phenomena due to the collective interaction of charges. Also: an analogous collection of charged particles in which one or both kinds are mobile, as the conduction electrons in a metal or the ions in a salt solution.

1928 I. LANGMUIR in Proc. National Acad. Sci. U.S.A. 14 628 It seemed that these oscillations must be regarded as compressional electric waves somewhat analogous to sound waves. Except near the electrodes..the ionized gas contains ions and electrons in about equal numbers so that the resultant space charge is very small. We shall use the name plasma to describe this region containing balanced charges of ions and electrons. 1930 Physical Rev. 37 1467 The plasma used in this investigation was the positive column of a mercury arc. 1958 Engineering 31 Jan. 134/2 The stable plasma reaches the high temperatures, of the order of 5 million deg. K., necessary for producing thermonuclear reactions. 1969 C. STEELE & B. VURAL Wave Interactions in Solid State Plasmas i. 4 In a metal like copper, the free electrons comprising the plasma are electrically compensated by the positively ionized copper atoms. 1971 E. NASSER Fund. Gaseous Ionization & Plasma Electronics xiv. 427 Liquid plasmas exist in salt solutions where the positive and negative ions move separately. 1976 T. BEER Aerospace Environment i. 16 The solar wind is a plasma of hydrogen ions (protons) and electrons travelling at speeds that range from 300 km s-1 to 1000 km s-1, depending on solar activity. 2001 South China Morning Post (Hong Kong) (Nexis) 12 Mar. 1 For up to 10 hours a day, he plays a game called Quake III..blowing holes in terrorists, watching their crimson innards splatter as he reloads his plasma gun.

So if we use this source, in general, we could write "In physics and chemistry, a plasma is a collection of particles or a fluid made of particles where some non-zero fraction of the particles is mobile and some non-zero fraction of particles is charged; the word plasma often refers to an ionized gas that is, on the whole, neutral. The particles may be fundamental particles and/or quasiparticles and/or composites such as atoms or molecules." To illuminate this definition, examples such as those above could be cited. For clarity, a gas made of neutral particles may be called a "neutral gas" and the article can distinguish between "ionized gases" and "neutral gases" rather than the vague or poorly used terms "plasmas" and "gases". --Zeroparallax (talk) 18:15, 5 April 2010 (UTC)

Or we could write, "In physics and chemistry, a plasma is an ionized gas containing free electrons and positive ions". --Art Carlson (talk) 21:08, 5 April 2010 (UTC)

That definition is too vague because "ionized gas" can be taken to mean 1) "a gas made of ionized particles" or 2) "the non-gas state reached after a gas has been ionized". As long as we clarify which phrase is usually meant, then it would be fine, and it's nice because it elaborates on the meaning of "ionized". That is, it would be fine assuming that the usual sense is captured by one of those two options; I'm not a plasma physicist, so I'm not sure. The person above (Adwol) who said "most of what I learned was how plasma is different to ionised gas" might disagree with these options, though! Anyway, this would be a satisfactory definition only if the rest of the article is made to agree with it. That means that if option 1 is selected, we would have to say "plasma" is a "gas" (a particular kind of gas), "plasma" is a different state or phase of matter than a "neutral gas", and almost every instance of the word "gas" in the article would have to be replaced by "neutral gas". If this is disagreeable, then I think it's necessary that the technical definition (after the lead, perhaps) not refer to gas but something else, such as "collection of particles". If both of these options are disagreeable, then I think it's a shame that so many physicists tolerate contradictory terminology, and we should explain the two different perspectives in the article.

Also, somewhere in the article we might want to mention these general(ized) uses of the word "plasma" that refer to mobile-charge fluids. --Zeroparallax (talk) 05:12, 6 April 2010 (UTC)

Ooh, I just found another cool generalized use of the word plasma on wikipedia itself, where not only "particle" is generalized to quasiparticle (a 2D vortex center), but "charge" is generalized to circulation direction (or "multiplicity", since it acts analogously to charge and could be called a charge). This can be found in the article on the Kosterlitz-Thouless transition in the Rigorous Analysis section.Zeroparallax (talk) 19:03, 22 April 2010 (UTC)

My contortions on this article and talk page

I just untangled the histories of plasma (physics), plasma, and their respective talk pages, after a botched history merge. A related talk page archive can be found at Talk:Plasma/Archive 1. Graham87 17:15, 23 January 2010 (UTC)

Viscosity

Someone please add some info about viscosity properties of plasmas! —Preceding unsigned comment added by 91.99.166.80 (talk) 13:58, 26 January 2010 (UTC)

Solar Wind density

Although shown in the Range of plasmas diagram, it isn't clear what the electron density of the solar wind is and this seems like an important figure.

Does anyone have a cited source for this? Makkasu (talk) 17:32, 27 January 2010 (UTC)

"Made of plasma"

Is it correct to say that stars are "made of plasma"? Isn't that like saying rocks are "made of solid"? Wouldn't it be more correct to say "stars are plasma" (or plasmas - I'm not sure what would be the most appropriate pluralization; "rocks are solid" and "rocks are solids" both seem reasonable but probably have subtly different meanings). Wardog (talk) 11:06, 25 February 2010 (UTC)

99.60.127.153 (talk) 23:20, 22 July 2010 (UTC) Made of plasma double layers in space would be what the public has been told is 'galactic lensing?'

Flame

Is usual flame a plasma? I heared that a flame over a candle can be moved by a magnet... —Preceding unsigned comment added by MathFacts (talk • contribs) 2010-04-19T15:28:39

Try Wikipedia:Reference desk/Science, please. - 2/0 (cont.) 16:10, 19 April 2010 (UTC)

I believe flame is intact atoms emitting light and heat. It's not plasma because the nuclei have their electrons intact and so it isn't extremely high temperature plasma. I guess flame is actually a "gas" that is emitting light because it is the visible chemical reaction of heat making chemicals or elements bond or split apart. Where the flame ends is the place where the gasses created cool down enough to stop emitting light photons, Radical Mallard (talk) 19:22, 15 July 2011 (UTC)

State of Matter?

Is plasma officially (or generally) accepted as a state of matter? The first sentence of the article calls plasma "A state of matter which..." A number of different sources (including websites, books, and people) are disagreeing on the topic, and I wondered if there was an official position taken up by any international boards or committees on whether plasma was a constant state of matter which could be achieved by any substance, or whether it was just a freak of nature that only affected certain elements and compounds. Awesome article, by the way. — Preceding unsigned comment added by Edocsil6437 (talk • contribs) 01:03, 16 March 2011 (UTC)

It is a state of matter, yes. solid, liquid, gas and plasma are the forms, I believe. Radical Mallard (talk) 19:22, 15 July 2011 (UTC)

Introduction Quote

"We shall use the name plasma to describe this region containing balanced charges of ions and electrons"

This obviously comes directly from an academic work of some sort, and the wording seems to implyimplies that this is not a standard definition, i.e., the normal definition is more general, and he is reducing ambiguity for the purpose of his work. As a non-expert, I think that it should be noted after the quote whether or not this article adopts the same convention. 74.94.233.237 (talk) 12:04, 5 July 2011 (UTC)

Er, yes, it is a direct quote from the source cited at the end of the quote - http://www.pnas.org/content/14/8/627. In 1928 the given definition of plasma was not the standard one because this state of matter was not called plasma until Langmuir. I have tried to clarify this; please come back or fix it if this does not help. - 2/0 (cont.) 16:21, 5 July 2011 (UTC)

3 Major Types of Plasma

Is it worth pointing out that there are 3 major types of plasma? (1) Electroplasma - free electrons and ions (atomic nuclei). (2) Nuclear Plasma - free electrons and protons (neutrons and neutrinos would escape). (3) Subatomic Particle Plasma - free electrons and quarks. (only existed at the early part of the Big Bang.) Each type has an order of magnitude higher temperatures. -- Radical Mallard (talk) 19:27, 15 July 2011 (UTC)

Introtext is misleading

After sufficient heating a gas dissociates its molecular bonds, rendering it into constituent atoms. However, further heating may also lead to ionization...

This suggests that plasma consists of ionized atoms and electrons. I tried to change that but user Materialscientist corrected that plasma can consist also of ionized molecules and electrons. So what is the fact? Also I think that plasma should be defined more popularily in the introtext. --PlasmaSoul (talk) 09:13, 14 August 2011 (UTC)

I've tried to rewrite that. Correct me at will. Plasma can be atomic or mixed atomic/molecular (or etc.), and the degree of molecular dissociation can be anything between almost 0 and almost 100%. Materialscientist (talk) 09:44, 14 August 2011 (UTC)

State of matter

I didn't see any citation for plasma being a forth state of matter. I came here looking for evidence of it but all I could find was a table that seems to be trying to show that it is a 4th state but it's not very convincing. Specific question I am left with: If gases become plasmas when they are ionized, why do liquids not have a separate state of matter when they are ionized? Calling plasma a separate state of matter seems premature since they are apparently still being heavily researched and it also seems like something self-important physicists would claim, hence why I am looking for the actual citations.

Also, why is this article restricted to (physics)? shouldn't it also have a (chemistry) entry or preferably none of these parentheses at all? esp. given its status as 4th state of matter it would be of interest to students of chemistry69.223.177.179 (talk) 23:24, 16 January 2012 (UTC)

"State of matter" is not such a well-defined concept that everyone agrees on what is or isn't a separate state, and consequently it isn't of central importance to the physical sciences. There is a disambiguation article on Plasma, without parentheses, but chemists will be interested in the same definition of plasma as physicists. Art Carlson (talk) 07:51, 17 January 2012 (UTC)