Are Electric Currents "Frozen In" to Plasma?

Many Internet forums have carried discussion of the Electric Universe hypothesis. Much of that discussion has added more confusion than clarity, due to common misunderstandings of the electrical principles. Here we invite participants to discuss their experiences and to summarize questions that have yet to be answered.

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Are Electric Currents "Frozen In" to Plasma?

Unread post by MGmirkin » Sun May 31, 2009 5:54 pm

A colleague online just asked a rather amusing question that has slightly expanded my consciousness, with respect to current mainstream understanding of plasmas and magnetic fields.

Astrophysicists refer to magnetic fields in plasmas as "frozen in" and "carried along with the plasma." However, we know from many sources that Maxwell's Wonderful Equations define a specific relationship between electric current and magnetic fields. Magnetic fields are a byproduct of electric currents. Granted, the feeling is mutual insofar as changing magnetic fields can induce an electric current. Hence electricity and magnetism are bound up in "electromagnetism." But how does this all apply to plasmas?

I'd refer folks back to Don Scott's paper on "Real Properties of Electromagnetic Fields and Plasma in the Cosmos."

Specifically, the section "VI. FROZEN-IN MAGNETIC FIELDS."
Don Scott wrote: Astrophysicists often assume that plasmas are perfect conductors, and as such, any magnetic field in any plasma must be “frozen” inside it ... It was based on the observation that, since plasmas were thought to be perfect conductors, they cannot sustain electric fields.

Alfvén’s original motivation for proposing “frozen-in” fields stemmed from another one of Maxwell’s equations, i.e.,

∇×E = −dB/dt

This implies that if the electric field in a region of plasma is identically zero valued (as it would have to be if the medium had zero resistance—perfect conductivity), then any magnetic field within that region must be time invariant (must be frozen). Thus, if all plasmas are ideal conductors (and thus cannot support electric fields), then any magnetic fields inside such plasmas must be frozen in, i.e., cannot move or change in any way with time.
But what of Maxwell's equations. Just because magnetic fields are considered "frozen in" to plasma, doesn't mean that no current exists. As I was thinking about it, the titular question of this thread came up. If magnetic fields were "frozen in" to plasma, wouldn't that imply that electric currents were also "frozen in" to the plasma?

If you think about it, it kind of makes sense in a twisted way (granted we know it's not true, 'cause plasma doesn't work that way)... IE, if the plasma were a superconductor (it's not, as can be easily demonstrated), then it could conduct a current essentially indefinitely without resistance. If a current flowed indefinitely, the magnetic field would be sustained indefinitely.

So, it seems to me like the statement that magnetic fields can be "frozen-in" to plasma is equivalent to saying that since plasma is considered a super conductor, any electric current causing or caused by the magnetic field would also have to be "frozen in" to the plasma (whatever that means).

So, the next time an astronomer mentions a "frozen in" magnetic field carried along with the plasma, I think I'll flip the script and ask him if that means it also has a "frozen in" electric current carried along with it... :?: *Wink*

Wonder what kind of a horrified, shocked reaction that will engender! :o

Anyway, on to disproving the "frozen in" condition completely... It's quite simple really, if you consider the above analogy. For plasma's magnetic fields to be "frozen in," it requires plasma to be a superconductor. A superconductor is a conductor where resistance is zero-valued and a current will flow indefinitely with no losses.
Wikipedia wrote:Superconductivity is a phenomenon occurring in certain materials generally at very low temperatures, characterized by exactly zero electrical resistance ...
http://en.wikipedia.org/wiki/Superconductor
Hyperphysics wrote:If a current is generated in a superconducting lead ring, it will persist because of the zero resistivity. Currents have been maintained in lead rings for several years to test the zero resistance condition. An induced current in an ordinary metal ring would decay rapidly from the dissipation of ordinary resistance, but superconducting rings had exhibited a decay constant of over a billion years!
http://hyperphysics.phy-astr.gsu.edu/hb ... is.html#c2
Is plasma a superconductor? Nope! (At the very least, not the low-density plasma of space, the sun's corona, etc. etc. It's doubtful that other plasma regimes are superconductive either.)

First a quick definition of terms.

Resistance R (measured in ohms) is considered to be the ratio of voltage V (measured in volts) to current I (measured in ampères). This can be simply expressed by the equation R = (V / I).

So, how can we know whether plasma's resistance is zero? Thankfully, there's a chart of plasma discharge regimes that comes in especially handy, as it compares voltage to current.

Image

As can be clearly seen in the plot of voltage versus current, the plot never touches the X-axis (or would that be the I-axis?)...

Pick any point on the voltage - current graph and draw a ray from the origin through that point. The ray will always have a positive non-zero slope, except AT the origin where there is zero current. Since V is never zero-valued, the entire expression (V / I) is never zero-valued (except at the origin where there is zero current). Thus R is never zero-valued. Resistance is non-zero for all current flowing through a low-density plasma (one assumes high density plasmas will also suffer resistive losses / joule heating).

Ergo, since plasma resistivity is non-zero, plasma is not a superconductor.
Even if it was a superconductor, and steady magnetic fields were frozen inside, it seems to me that steady electric currents would also have to be frozen inside... Ya' can't get away from them that easily!

Returning to Don Scott's paper for a moment, his remarks thus seem cogent:
Don Scott wrote:Thus, although plasmas are excellent conductors, they are not perfect conductors. Weak longitudinal electric fields can and do exist inside plasmas. Therefore, magnetic fields are not frozen inside them ... Now, we know that there are slight voltage differences between different points in plasmas. Many astrophysicists are still unaware of this property of plasmas, and so, we often still read unqualified assertions ...
Don Scott wrote:VII. CONCLUSION

Maxwell showed that magnetic fields are the inseparable handmaidens of electric currents and vice versa. This is as true in the cosmos as it is here on Earth. Those investigators who, for whatever reason, have not been exposed to the now well-known properties of real plasmas and electromagnetic field theory must refrain from inventing “new” mechanisms in efforts to support current-free cosmic models. “New science” should not be invoked until all of what is now known about electromagnetic fields and electric currents in space plasma has been considered. Pronouncements that are in contradiction to Maxwell’s equations ought to be openly challenged by responsible scientists and engineers.
Astrophysicists can put that in their pipe and smoke it! :twisted:

Regards,
~Michael Gmirkin
Last edited by nick c on Fri Apr 20, 2012 2:20 pm, edited 1 time in total.
Reason: Link (Scott's paper) updated
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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by longcircuit » Sun May 31, 2009 8:07 pm

Oh, Mike, you little imp of the perverse, you. That's an excellent insight. Let's see Phil "It has to be that way for the math to work" Plait wriggle out of it. I wonder if he'd invoke a "dynamo" internal to the magnetic field, much like the one supposed to cause the Earth's magnetism.
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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by redeye » Mon Jun 01, 2009 4:31 am

If you think about it, it kind of makes sense in a twisted way (granted we know it's not true, 'cause plasma doesn't work that way)... IE, if the plasma were a superconductor (it's not, as can be easily demonstrated), then it could conduct a current essentially indefinitely without resistance. If a current flowed indefinitely, the magnetic field would be sustained indefinitely.
If plasma conducted electricity, without resistance, wouldn't all the charge in the Universe be equalized instantly? Hence, no Universe (as we know it).

If the electric star hypothesis is correct then I believe that everything we observe in the Universe is simply resistance, I'm including human beings in that.

Great weapon against the entrenched dogma of the mainstream. Fine work as usual Micheal.

Cheers!
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Bob Marley

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by MGmirkin » Mon Jun 01, 2009 9:58 am

redeye wrote:If plasma conducted electricity, without resistance, wouldn't all the charge in the Universe be equalized instantly?
Well, yes and no, I think... That does seem to be the thought behind the notion of frozen-in magnetic fields and the notion that the universe is rules by gravity rather than by electric currents.

In other words...

Assume plasma is a superconductor with zero-valued resistance.
If plasma superconducts, then charges instantly neutralize.
If charge neutrality is total, then no electric fields.
If no electric fields, then no currents.
If no currents, then gravity rules.

Premise 1 appears flawed. Plasma does not superconduct. (Certainly not the low-density plasma of space, and most likely not the medium or high-density plasmas either.)

Ergo charges do not instantly neutralize. Ergo there are regions of differing charge within a plasma. Ergo electric fields can and do exist within a plasma. Where electric fields exist, non-neutral particles respond 36 orders of magnitude more strongly to imbalanced electromagnetic forces than gravitational forces. Currents flow, currents generate magnetic fields. Magnetic fields are not "frozen in" to plasma. The case for an electrically neutral universe is weakened considerably.

Just my opinion, of course.
~Michael Gmirkin
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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by M5k » Wed Jun 03, 2009 9:16 am

MGmirkin wrote: If plasma superconducts, then charges instantly neutralize.
Wouldn't this also require that charge carriers are able to move from point A to point B instantaneously?

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by Tzunamii » Wed Jun 03, 2009 11:15 am

M5k wrote:
MGmirkin wrote: If plasma super conducts, then charges instantly neutralize.
Wouldn't this also require that charge carriers are able to move from point A to point B instantaneously?
You took the thought right outta my head.
It would definitely conflict with the "universal speed limit" as I've understood it.
If in fact there were one, which I'm not convinced.
It's become commonplace to see mainstream ideas contradict each other, with nary an explanation, or even acknowledgment.

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by MGmirkin » Wed Jun 03, 2009 11:59 am

M5k wrote:
MGmirkin wrote: If plasma superconducts, then charges instantly neutralize.
Wouldn't this also require that charge carriers are able to move from point A to point B instantaneously?
Ohh, did I forget to put that part in? Meant to, but I forgot.

Yeah, I always thought it was a bit weird, the whole "instant neutralization" thing. IE, if you've got a relatively large region with a charge imbalance, how long will it take for the constituents to physically move back into balance? Especially when we're talking scales of solar systems, galaxies and the universe at large? And when we're also talking about resistance, turbulence, friction or what have you... (Maybe friction is the wrong word, but you get the idea.)

Best,
~Michael Gmirkin
"The purpose of science is to investigate the unexplained, not to explain the uninvestigated." ~Dr. Stephen Rorke
"For every PhD there is an equal and opposite PhD." ~Gibson's law

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by lalbatros » Sun Sep 20, 2009 1:55 am

Is plasma a superconductor? Nope! (At the very least, not the low-density plasma of space, the sun's corona, etc. etc. It's doubtful that other plasma regimes are superconductive either.)
(MGmirkin)
It is the first time I read this question: "Is plasma a superconductor?".
I thought that the Spitzer resistivity was a widespread mainstream concept.
For example, when electron-ion collisions dominate, the Spitzer resistivity is given by:

res[nanoOhm m] = 1.65 ln(Coul)/Te^1.5

where

Te is the electron temperature
Ln(Coul) is the famous "Coulomb logarithm given in the special case by:

ln(Coul) = 15.2 - 0.5*ln(ne) + ln(Te)

where

ne is the electronic density in 10^20 per m³
Te is the electronic temperature expressed in keV

A simple inspection of the Spitzer formula shows that:

- the resisitivity decreases very fast with the temperature
- it decreases logaritmically with the electronic density

Therefore, I do not understand very well why your remark in the brakets:
Is plasma a superconductor? Nope! (At the very least, not the low-density plasma of space ...
For sure a plasma is not a superconductor.
But at least, its resistivity decreases with the density, which makes it a closer to a superconductor even if it will never become a superconductor. Obviously, in the limit of extremely low densities, a plasma becomes a superconductor, at least on time scales smaller than the resistive diffusion time which is larger for lower densities.

To be more serious, I think that a sound discussion of this topic should at the least involve the statement of some basic information like:

- the charge densities considered and the composition (hydrogen + ... ?)
- the temperatures
- the scales
- the currents involved
- size and shape of the system considered
- durations considered (hours, years, million years, ...)

From this a few elementary data should be derived like:

- collision frequencies
- resistivities
- Debye length
- characteristic time for charge neutralisation (to check for possible quasi-neutrality)
- resistive diffusion time
- Alfven time
- magnetic Reynolds number (S)

The answer to the original question "Are Electric Currents "Frozen In" to Plasma?" is simply answered by the magnetic Reynolds number.
Large S implies frozen-in magnetic field lines.
Small S means "difusion" of the magnetic field lines.

Sceptical regards,

Michel


PS
==
As I am new, is there a way to write equations on this forum?
It is obviously better to write equations when discussing physics.

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by bboyer » Sun Sep 20, 2009 2:48 am

lalbatros wrote:...

PS
==
As I am new, is there a way to write equations on this forum?
It is obviously better to write equations when discussing physics.
Sorry, all we offer that might minimally help are:

Code: Select all

subscript [sub]subscripted text here[/sub]
superscript [super]superscripted text here[/super]
strike-through [strike]strike-through text here[/strike]
They have to be coded manually as you compose your message. subscript; superscript; never mind
There is something beyond our mind which abides in silence within our mind. It is the supreme mystery beyond thought. Let one's mind and one's subtle body rest upon that and not rest on anything else. [---][/---] Maitri Upanishad

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by lalbatros » Sun Sep 20, 2009 12:36 pm

I was quite surprised when reading this quote from Don Scott in IEEE (1):
Don Scott wrote:
Astrophysicists often assume that plasmas are perfect conductors, and as such, any magnetic field in any plasma must be “frozen” inside it ... It was based on the observation that, since plasmas were thought to be perfect conductors, they cannot sustain electric fields.

Alfvén’s original motivation for proposing “frozen-in” fields stemmed from another one of Maxwell’s equations, i.e.,

∇×E = −dB/dt . . . . . . . . . . . . . . (12)

This implies that if the electric field in a region of plasma is identically zero valued (as it would have to be if the medium had zero resistance—perfect conductivity), then any magnetic field within that region must be time invariant (must be frozen). Thus, if all plasmas are ideal conductors (and thus cannot support electric fields), then any magnetic fields inside such plasmas must be frozen in, i.e., cannot move or change in any way with time.
First, I have searched the paper for comments about the use of the total derivative dB/dt instead of partial derivatives in eq 12.
There is no comment at all in Don Scott paper although this might be essential!
Also, nowhere he mentions an eventually special meaning for the E and B fields.
Therefore, I can only assume that E and B are the usual electric and magnetic fields in an inertial frame.
And therefore also, I can only assume the derivatives he writes are the partial derivatives δB/δt from the standard way of writing Maxwell's equation.
I will write partial derivatives as δB/δt, since the needed character is not available here.
I am obliged to make these assumptions, in the absence of any comment by Don Scott.

Don Scott is then wrong to assume that the "frozen-in" fields cannot move or change with time.
From my many readings in physics, I have absolutely never read such a statement.
Not one astrophysics would ever make such a claim either, as this contradicts elementary physics! (see ref 2 for example)
This is not at all the meaning a of the "frozen-in" theorem of the MHD approximation.
The meaning rather is that the magnetic fields move together with the plasma, in this approximation.
And there are no reasons why the plasma could not move!

It seems this is more than a descriptive mistake by Don Scott.
Indeed, starting the argument with the Faraday equation and assuming E=0 everywhere is the mathematical translation of this misunderstanding.
This leads him to the conclusion that B in this case should be stationary, which is also wrong.
In the MHD approximation, there can be an electric field in a plasma, and moreover the magnetic field can change with time.
The (MHD) assumption of an infinite conductivity translates rather as follows: E+vxB = J/σ = 0 .
The "motional electric field" defined by Em = E + vxB, is zero in the MHD approximation.
It is wrong to assume that the electric field itself would be zero.

It is this simple fact that allows us to understand the meaning of "frozen-in" field lines in the MHD approximation.
Instead of being zero, the electric field is actually given by: E = -vxB.
Plugging this expression in Faraday's law we get:

∇×(-v x B) = -δB/δt

From elementary calculus (3), this implies that the resulting magnetic flux through any contour co-moving with the plasma is constant.
Therefore, this can be called the "frozen-in equation".

It should be kept in mind that this is only one of the many approximations in plasma physics.
The closest approximation is of course "resistive MHD".
Resistive MHD is simply obtained by including the term J/σ in the "frozen-in equation" above:

∇×( J/σ - v x B) = -δB/δt

This simply leads to an additional diffusion term.
More detailled models consider electrons and ions separately with collisional and electromagnetic interactions.
Much more detailed models consider the full velocity distribution of each charged species.

For example, the electron distribution might contain a fast component superposed to a bulk thermal component.
In this case, the MHD does not apply at all and the full particle details have to be accounted for.
This occurs for example for run-away electrons in tokamaks, or for neutral beams injected and ionized in a tokamak plasma.
The physics involved is very far from simple MHD, although some MHD aspects can surface sometimes.

It is actually easy to answer the initial question "Are Electric Currents "Frozen In" to Plasma? ".
The answer is simply: generally they are not frozen-in.
This is mainstream understanding.
However, the frozen-in conditions are often met in practice, at least approximatively.
Therefore, the question is more about the appropriate use of an approximation.
That's day-to-day business in physics!

Sceptically yours,

Lal

(1) http://members.cox.net/dascott3/IEEE-Tr ... ug2007.pdf
(2) The physics of fluids and plasmas: an introduction for astrophysicists By Arnab Rai Choudhuri, Cambridge University Press
(3) Advanced engineering mathematics By Alan Jeffrey, 2002, Academic Press

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by jjohnson » Fri Sep 25, 2009 12:02 pm

Yay! Some dialog with supportive math, and resulting possibility (I hate to say probability or even likelihood) of critical thinking applied here to us, amateurs at work. Especially moi!

I think part of the speed at which ionization could be neutralized in a superconductor is "very fast" since all you have to do is get the unlike charges together, assuming there are equal numbers of each, and they have to cross distances that may be up to several meters. However, they do that at less than c. However, the recombination would occur all up and down a "filament" or the DeBye length or whatever, more or less simultaneously. All this thought experimentation begs the reality question, though. That is, if the plasma were a perfect superconductor, could you get it to be ionized in the first place? If it "got ionized" with separation of charges, what initiates its sudden return to superconductivity and charge reassembly? See? Too much thought experiment and not enough real life observation of what these plasmas really are.

First, they seem to be "good" conductors. Second, they exist in circuits, and circuits have lcr components that may cause oscillatory phenomena (pumping), and resultant field variations, resulting in different electron velocities, pinching and relaxation, etc. Third, they exhibit irregular resistances. Part of this is that they can range from simple ion, electron and atomic/molecular compositions to having dusty, grainy or rocky inclusions. Lumpy plasma at a variety of scales. Fields and motions under these conditions vary accordingly and also require some corrections. Peratt's text includes (Appendix C, p325) consideration of particle motion under these particular conditions, for various particle densities. Interestingly, this leads early on to his conclusion as to how stars form: dusty plasmas are created, with the smallest particles, motion dominated by the electromagnetic term in the equation of motion. These can accrete to (or the plasma may simply include existing) larger particles wherein plasma effects still play a major role in the system dynamics, and the charge to mass ratio (q/m) is approximately the square root of the gravitational constant G. If the grain size becomes "large" enough the electromagnetic term is negligible, and viscosity and gravity tend to dominate. For large solid bodies, dynamics is governed by gravity less the viscosity term. This is not meant to be a parroting of Appendix C, but to simply show that there is a complex interplay of many elements at work here, and that resistance and conductance may be ordered via several mechanisms, and those are not solely the EM fields we all want to understand better, but other stuff too. Peratt thinks that once dusty plasmas exist, that there can be a path through sedimentation into "stellesimals" - chunks - and then collapse into a stellar state. Compared with jets, stars are paradigms of stability.

I might add that the collapse seems (to me) less a passive event than precipitated by and hastened by the pinch effect. Just as with the formation of visible clouds on Earth, with well-defined transitions between clear air and air with saturated water vapor droplets, just where a pinch is going to occur and result in a star's birth, up and down the semi-chaotic conditions in a cosmic Birkeland current or current sheet, I don't know. If we could figure that out, the solar "space weather" in our own backyard should be a snap! That the conditions for star formation are less ripe between galaxies is obvious; that they become ideal for galactic-wide star formation with galaxies is equally obvious: "in this place thar be stars" but why here and not there is just one more question. Circuit theory on the grand scale! Maybe a galactic regions is one where there are sufficient extra particles in a variety of sizes for currents to engage and incorporate. Then when a pinch occurs it can take 20 parsecs of loose rubble and gas and compress it into a relatively dense star-mass, and light it off with its collapsing drift current. Which comes first, the plasma drift current or the stellar magnetic fields and internal stellar circuitry which attract the drift current? How a star lights off, and over what timescale, would be an interesting observation. Between galaxies, not so much rubble and very low particle density in currents, and not enough matter to incorporate and create a lightable pinch. Is one entire galaxy at a different voltage level than the next one, in order to induce current flow from one toward the next?

The shortest journey always begins with a thousand steps.

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by mharratsc » Wed Sep 30, 2009 1:07 pm

How about putting it this way?

Nowhere in our naturally-viewed Universe have we discovered any form of plasma to be superconducting.

This statement is based off of the experimental results of plasma physicists in lab experiments, and even astrophysicists (such as Alfven) whose primary aim was to study the characteristics of plasmas in space without any pre-conceived notions.

Experiential data.

How then can the claim be made that frozen-in magnetic fields are often met "in practice"??

Mathematics practice??

The only explanation can then be: the practice does not take place in reality.

If your formula shows you one thing, but experiments in reality show you another... what should you do then?

Mike H.
Mike H.

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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by lalbatros » Fri Oct 02, 2009 9:51 am

mharratsc wrote:How about putting it this way?

Nowhere in our naturally-viewed Universe have we discovered any form of plasma to be superconducting.

This statement is based off of the experimental results of plasma physicists in lab experiments, and even astrophysicists (such as Alfven) whose primary aim was to study the characteristics of plasmas in space without any pre-conceived notions.

Experiential data.

How then can the claim be made that frozen-in magnetic fields are often met "in practice"??

Mathematics practice??

The only explanation can then be: the practice does not take place in reality.

If your formula shows you one thing, but experiments in reality show you another... what should you do then?

Mike H.
Hi Mike,

I worked for nearly 10 year in nuclear fusion on tokamaks.
That's what I mean first by "in practice".
I could write pages on this practice, but you could just take one of the many books on the topic.
One of my first job was about the equilibrium of the tokamak plasmas and how its position and eventually its shape can be controlled by the various external currents used for this purpose. It is not so often in plasma physics that theory is a reliable basis for engineering. In that specific case, the MHD approximation assuming infinite conductivity works pretty well. There is no need for more when solving this equilibrium problem. That's engineering practice.

This illustrates a point that apparently posters on this site have much difficulty to understand.
A theory, in itself, is of absolutely no value.
I mean this for all theories, absolutely all theories.
The value of a theory exists only when it is applied correctly and when its domain of applicability is known (reasonably at least).
Till today, there are no theories that can be applied in every circumstances without taking any care for its applicability.
Some theories do have a much broader range of applicability.
However, more general theories are always more difficult to use on specific questions and some approximations needs to be used for applications.
This is just why MHD theory has been designed.
Actually the general theory of plasma is perfectly known and quite simple: the motion of charges and electrodynamics make the whole plasma physics.
But the general theory is not directly usable and in the end we practically work with approximations.

The ideal MHD is indeed a very good example in this respect.
It applies very well to predict plasma equilibrium in a tokamak.
Well, actually, not really without any limits, and even for apparently equilibrium problems.
For example, when the velocity distribution of the particles is highly assymetric for very hot plasmas, then the standard MHD approximation is not a good approximation anymore and it needs at least some corrections. Starting with the basic laws of motion for particles, it is possible to develop much better approximations than ideal MHD, that are not necessarily much more complicated than simple ideal MHD. These laws could then take the effect of an anisotropic distribution into account and its influence on the plasma equilibrium. This is essential in the diagnostic of very hot tokamak plasmas. For example, this must be taken into account in order to measure the total energy of the plasma volume based on the measurements of external equilibrium currents.

For slow motions of the plasmas, like the rotation of a magnetic island, the simple ideal MHD can also be a good model ... still within the right limitations (small gyroradius for example).
However, when fast motions are involved, like during global disruptions or during internal partial disruptions (tokamak sawteeth oscillations e.g.), the ideal MHD model is almost totally irrelevant (like the scenery versus the story).
In this case, the next simple model is resistive MHD that takes resistivity effects into account.
This model is derived from the general laws, just like MHD, but the approximations made are "better".
This model is useful as it shows clearly when and why a plasma can become unstable.
It has -at least- shown the existence of a wide range of plasma instabilites called "resistive instabilities".
However, it is generally unable to explain the speed of these events (same as for space plasmas).
Till today, I think that there are still no totally satisfying theory of disruptions.
However, there is an understanding of the complex phenomena that are involved, based on the general laws.
These general laws (moving particles + electrodynamics) have never yet shown any sign of invalidity.
Instead, by improved (yet still approxilmate) solutions have shown their abilities to explain plasmas in general.
(and also quatum plasmas like in solid state physics!)
Definitvely, the ultimate theory needs to consider the particles motion in some detail in other to understand the full story.
The MHD is unusable to analysis these things.

Now I already ear your your little voice: ... theory and no experience ...
Read again what I just said.
Is it not clear that without theory your observations have just no meaning?
Not more meaning than a train for a cow.
So, Mike, you should introspect on your own statement:

"Nowhere in our naturally-viewed Universe have we discovered any form of plasma to be superconducting. "

How do you know that there is no superconducting plasmas in the universe?
Is your eye able to measure conductivity?
And what do you mean by superconducting?
Do you mean that a superconding current should last more than a human lifetime, 100 years?
And after all, do superconductors really exist?
Till today, nobody has ever proved that a superconducting current could last more than 1000 year.
Or at least, this was not done by pure observation, some theory should have been used.

Learn this, Mike: in physics you always need to consider the error bars, even in your statements.

Very sceptically yours,

Michel

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Birkeland
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Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by Birkeland » Fri Oct 02, 2009 12:07 pm

lalbatros wrote:I worked for nearly 10 year in nuclear fusion on tokamaks.
Thanks for sharing your thoughts on the subject. I've more than often felt a bit skeptical to the whole tokamak concept. It seems backward or incomplete in the sense that you're not getting to the core, but are working in an outside toroidal range compared to inertial electrostatic confinement fusion. I'm referring to the Polywell concept that, in theory, works by electromagnetic trapping of electrons in a central chamber. Any comparative thoughts on the tokamak and the polywell concept would be welcome.
"The hardest thing to explain is the glaringly evident which everybody had decided not to see" - Ayn Rand

lalbatros
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Joined: Sat Sep 19, 2009 1:12 pm

Re: Are Electric Currents "Frozen In" to Plasma?

Unread post by lalbatros » Sat Oct 03, 2009 1:00 pm

Till today I did not know about the Polywell device. Therefore I have read this paper:

http://askmar.com/ConferenceNotes/Shoul ... uclear.pdf

Its reading was rather depressing for me as it looks like expensive amateurism.
In tokamak research, I have experienced what Dr Bussard precisely called "really good science" (page 4).
I was specially impressed by the wide range of plasma diagnostics that were developped and the amazing observations that were obtained.
These experimental results are a very weighty foundation to improve the theoretical understanding.
I doubt that nuclear fusion could be reached without "really good science".
This is unpopular but very probable.

As far as the EU hypothesis or the "frozen in" current question are concerned, the polywell device is totally irrelevant.
The largest and hottest laboratory plasma have been obtained in tokamaks.
Therefore tokamak research is probably one of the best earth-based source of information on plasma physics.
It makes sense to learn from tokamak research when discussing the EU hypothesis.

More specifically, it should be clear, specially for Mike, that ideal MHD, the frozen in question and many other elementary topics in plasma physics are very well understood and are in no way "mathematical abstractions disconnected from reality".
Having such kind of prejudices is of no use in a scietific discussion.
On the contrary, the mathematical models are perfectly useful and can be compared quantitatively to experimental results.
This means first of all that their range of applicability is reasonably known, and this is also part of the theory.

However, plasma physics is actually much more complicated that most posters here seem to undertand.
It is extremely surprising for me that people claiming a new cosmological hypothesis based on plasma physics are so little aware of real plasma physics both experimental and theoretical.
On the experimental side, it is quite funny that they seem to know more about the Z-pinch than about the tokamak!
Yet, there is quite a lot of physics to be observed and analysed going on in tokamaks!
On the theoretical side, I can't understand why the discussions here never goes beyond elementary MHD questions.
Yet it is obvious, both experimentally and theoretically, that MHD is not more than a simple approximation with a very restricted domain of applicability.

Looks like science ... but this is homework science with simple questions and many wrong answers.

Might be useful to know ...

Michel

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