Magnetic reconnection and physical processes

Zeuzzz said:

Dare is ask why Fälthammars peer reviewed publication on the concept of moving magnetic field lines has invoked such a reaction? I find his point that belchers moving magnetic field line velocity is only valid when B × curl [B(E•B/B²)] = 0 quite satisfactory, likewise his example of a time-independent magnetic dipole field in the presence of a homogeneous electric field parallel to the dipole axis. But I am presuming you have a good reason to dismiss this?

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That link appears to be dead, this one should work instead: On the Concept of Moving Magnetic Field Lines http://sprg.ssl.berkeley.edu/adminstuff/webpubs/2007_eos_169.pdf

More than 99% of the known matter in the universe is ionized into the plasma state. This cosmical plasma is generally permeated by magnetic fields. Hence, magnetic fields, and the concepts of magnetic field lines and magnetic field line motion, are of fundamental interest in the physics of space plasmas, including those that constitute the near environment of the Earth and other planets.
W. Belcher discussed the concept of magnetic field line motion as a useful tool in teaching electromagnetic theory in an article in Eos [Belcher, 2005]. However, there are some important limitations and pitfalls to this concept, none of which is mentioned in the article by Belcher

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Or this one: http://scitation.aip.org/getabs/ser...00074000005000454000001&idtype=cvips&gifs=yes

Belcher and Olbert recently showed that the concept of the motion of magnetic field lines can be helpful in teaching classical electromagnetism. Although this concept holds in many situations, it has important limitations. It is shown that the most common definition, v=E×B/B2, which is the one used by Belcher and Olbert, is not appropriate when an electrostatic field is present, unless the field satisfies special conditions. In an infinitely conducting medium where the electric field has no component parallel to the magnetic field, E×B/B2 is still a meaningful definition of the motion of magnetic field lines (which follow the plasma motion as if "frozen-in"). It used to be assumed that space plasmas could be treated as infinitely conducting and therefore the concept of magnetic field line motion was used extensively. But local nonvanishing values of E·B can "cut" magnetic field lines and invalidate the frozen-in condition.

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Ziggurat said:

No photons needed.



The energy for the spark comes from the magnetic field. The decrease in the magnetic field that occurs after you unplug it induces an electric field, and that electric field pushes the spark across the gap, but the energy to do so was stored in the magnetic field.

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How is that stored energy going to be conveyed to anything without photons?

I am sorry, but Karl-Gunne is just nitpicking in those two publications.
These days peeps are well aware of the breaking down of the frozen in condition, several papers have been published lately to specifically look at the breaking down of the frozen in condition Here is a paper by Rikard Lundin which concludes:

Lundin et al. said:

Our test suggests that ideal MHD applies in a macroscopic sense in major parts of the outer magnetosphere, for instance, in the external cusp and in the high-latitude magnetosheath. However, we also find significant departures from ideal MHD, as expected on smaller scales, but also on larger scales, near the cusp and in the magnetosphere-boundary layer. We discuss the importance of these findings.

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And in the Earth's magntotail the same has been investigated by Tony Lui.

One just has to know when MHD applies and when not, that is what Fälthammar's paper is really about. Is the magnetic field moving along with the plasma or not, not whether magnetic fields can move at all or not.

So, frozen in field will not happen very near the X-point of reconnection, because first there is a region where the ions are decoupled from the field (ion diffusion region), and even further in the electrons decouple from the field (electron diffusion region).

Magnetic Reconnection Redux VII

There is much discussion of magnetic reconnection buried in the depths of several threads which do not obviously pertain to the topic, and probably should not. But in any case, I like the idea of concentrating discussion of reconnection in its own thread, if only to avoid the confusing profusion of topics in threads, not necessarily related to the OP thereof. So I will put this here and see what happens.

Regarding magnetic reconnection, Mozina as told us ...

Michael Mozina said:

... starting with the fact you can't even physically distinguish it from "induction" and "circuit reconnection" at the level of actual physics. The transfer of energy from the magnetic field to the charged particle is called "induction" and it has nothing to do with "magnetic reconnection".

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What is "circuit reconnection"?
Let me start by pointing out that Mozina has never given any indication, at the level of real physics, as to what the words "circuit reconnection" (or "particle reconnection" as he sometimes puts it) are supposed to mean. If we simply look at simple electric currents, and assume that the currents merge, then what happens to the kinetic energy of the particles in the circuit? The total kinetic energy of the particles in the final merged current cannot exceed the total kinetic energy of the particles in the merging current, absent an influx of energy from other sources. That's why I have said (and Mozina has resolutely ignored) that "circuit reconnection" cannot be what's happening because it violates the well accepted principle of conservation of energy. My position may change, pending some more informative explanation of what "circuit reconnection" is supposed to mean. But see post #3209 by ben_m in the plasma cosmology thread for additional insight into currents & fields regarding circuit reconnection.

What is magnetic reconnection?
My authoritative source for the physics of magnetic reconnection is the book Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes, Cambridge University Press, 2000. Let me quote from the introduction (page 1): "As we shall discuss in more detail later on, reconnection is essentially a topological restructuring of a magnetic field caused by a change in the connectivity of its field lines." And in the following paragraph we find this: "The evidence of reconnection in laboratory fusion machines such as the tokamak and the reversed field pinch is so strong that there is no longer any controversy about whether reconnection occurs, but only controversy about the way in which it occurs."

Why not induction?
Now, Mozina insists that what we are really seeing is induction. Is this a reasonable assertion? At the level of real physics it appears to be unrealistic. We know that induction is invariably constrained (or unconstrained) by the characteristic diffusion time for the magnetic field in a given environment. Remember that in the process of induction, the magnetic field move with respect to the charged particles, and it is that relative motion between field & particle that determines the transfer of energy from the magnetic field to the particles. Let me quote once again from Priest & Forbes, this time from section 1.1 ("The Origins of Reconnection Theory"), pages 6-7: "For example, solar flares release stored magnetic energy in the corona within a period of 100 s. By comparison, the time-scale for magnetic dissipation based on a global scale length of 10⁵ km is of the order of 10⁶ yrs. Typically, phenomena like the solar flare and the substorm require a significant fraction of the stored magnetic energy to be converted within a few Alfven time-scales. Such rapid time-scales are easily achieved in ideal MHD processes, but not in non-ideal ones. Although ideal MHD processes can release energy quickly, they rarely release a significant amount because of the topological constraints which exist in the absence of dissipation. In contrast, magnetic reconnection is not topologically constrained, and therefore it can release much greater amounts of energy (Kivelson and Russell, 1995)."

Are magnetic field lines physically real?
The concept of field lines was devised by Michael Faraday and adopted by James Clerk Maxwell, whom we recognize as the principle architect of classical electromagnetic theory and the more general classical field theory. Whether or not field lines are physically real is magnificently irrelevant, but a great red herring for anyone who wants to avoid the real physics. The name "magnetic reconnection" comes from the mathematical formulation (theory) for the physical process (observation). The equations use the topological reconfiguration of mathematical field lines to describe the topological reconfiguration of the magnetic field, as it is observed to happen. The point is that a physical process is seen to take place, and a mathematical formalism to describe that process is in place. In every respect, the predictions of the mathematical formalism are consistent with the observed processes. As long as the mathematics and the observed physics are mutually consistent and compatible, it is a matter of no consequence at all, whether or not the "field lines" represented in the mathematics directly correspond to physical lines of magnetism.

Here is a small list some of my own posts on the topic of magnetic reconnection, mostly from the plasma cosmology thread.

• Magnetic Reconnection Redux VI
• Magnetic Reconnection Redux V
• Reconnection is not induction
• Magnetic Reconnection Redux IV

Tim Thompson said:

What is "circuit reconnection"?
Let me start by pointing out that Mozina has never given any indication, at the level of real physics, as to what the words "circuit reconnection" (or "particle reconnection" as he sometimes puts it) are supposed to mean.

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It's a "short circuit" between two current carrying "magnetic ropes". Is that clear enough?

I'm going to have to nibble at your posts after work Tim, but your notion of "magnetic reconnection' being a unique form of energy exchange is going down.....

Thanks tim, but if you could answer each of the questions in the OP I think that would resolve any issues far quicker than your long posts summarizing the theory.

Zeuzzz said:

Thanks tim, but if you could answer each of the questions in the OP I think that would resolve any issues far quicker than your long posts summarizing the theory.

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I think that Tim's answer to all of the questions would be:
Read Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes, Cambridge University Press, 2000.

The OP questions basically ask to give a complete explanation of every part of the theory and applications of magnetic reconnection.

RC, pontificate all you want. Questions were asked in the OP and you have not answered them. Which leads me to think that either you dont know the answer or magnetic reconnection theory is in such a confused state an answer can not be given.

Some people like Sol and Ben tackled a couple of simpler questions, but as for all the original questions as they were asked in the OP, no-one has answered completely.

Zeuzzz said:

RC, pontificate all you want. Questions were asked in the OP and you have not answered them. Which leads me to think that either you dont know the answer or magnetic reconnection theory is in such a confused state an answer can not be given.

Some people like Sol and Ben tackled a couple of simpler questions, but as for all the original questions as they were asked in the OP, no-one has answered completely.

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Zeuzzz, pontificate all you want.
Questions were asked in the OP and I do not intend to answer them because it is not my area of expertise.

I know that magnetic reconection theory is in enough of a coherent state that textbooks can be written on it, e.g. Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes, Cambridge University Press, 2000.

The complete, comprehensive answer to

Zeuzzz said:

I am after the whole process, from the topological change in the field lines representing the magnetic vector field around the formation of the neutral point (often respresentaed as an X type neutral line) all the way through to how the energy is physically released from the topology of the lines in this system.

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is read Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes.

The complete, comprehensive answer to

Zeuzzz said:

A) The difference between field lines reconnecting in the formation of a standard neutral point and what physically occurs (if anything) when this happens, and what physically occurs in magnetic reconnection used to explain various energy releasing mechanisms in astrophysics.

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is read Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes.

etc.

The short, basic and incomplete answer is (as described in this thread and others):
Magnetic field lines reconnect and the magnetic energy stored in the field is transfered to the charged particles in the plasma.

Reality Check said:

Zeuzzz, pontificate all you want.
Questions were asked in the OP and I do not intend to answer them because it is not my area of expertise.

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Well thats all you need to say, RC. You cant answer the questions. Hopefully someone else will.

Zeuzzz said:

Well thats all you need to say, RC. You cant answer the questions. Hopefully someone else will.

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What I said is that it is my guess that no one will because the OP basically asks for a complete description of the theory and applicaitons of magnetic reconnection.
Thus no one will answer the questions in the OP.

Other posters have handled this by stating the basics or by pointing you to other discussions, e.g.

tusenfem said:

Yes, that is the very simplified description of reconnection. However, you need to take into account that the "density of field lines" gives the magnetic field strength and in the "reconnection region" naturally the field strength goes to zero and the idea of a field line does not make sense anymore.

Apart from that "when the field lines suddenly straighten" that is caused by the magnetic tension, just like a pulled string.

For the rest, I have discussed reconnection in its simple form on BAUT and I don't feel like copy-pasting. Because there are several follow up posts. I guess I will have to put this into my "plasma physics for dummies" document, that I am producing for BAUT.

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Zeuzzz said:

Thanks tim, but if you could answer each of the questions in the OP I think that would resolve any issues far quicker than your long posts summarizing the theory.

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Funny, I thought that the questions in the OP were each answered!

Which questions do you feel have not been answered, Z?

What parts of the answers given by various folk (tusenfem, sol, Zig, ...) did you not understand?

Tim Thompson said:

Are magnetic field lines physically real?
The concept of field lines was devised by Michael Faraday and adopted by James Clerk Maxwell, whom we recognize as the principle architect of classical electromagnetic theory and the more general classical field theory. Whether or not field lines are physically real is magnificently irrelevant, but a great red herring for anyone who wants to avoid the real physics. The name "magnetic reconnection" comes from the mathematical formulation (theory) for the physical process (observation). The equations use the topological reconfiguration of mathematical field lines to describe the topological reconfiguration of the magnetic field, as it is observed to happen. The point is that a physical process is seen to take place, and a mathematical formalism to describe that process is in place. In every respect, the predictions of the mathematical formalism are consistent with the observed processes. As long as the mathematics and the observed physics are mutually consistent and compatible, it is a matter of no consequence at all, whether or not the "field lines" represented in the mathematics directly correspond to physical lines of magnetism.

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Isnt that an example of Newtonian thinking?

It doesnt matter how or why it happens. Only that we can measure it and calculate the results.

My question would be "Would a PIC simulation be more "realistic" than a MHD approximation"? Are frozen in fields an artifact of the MHD approximation?

Tim Thompson said:

Here is a small list some of my own posts on the topic of magnetic reconnection, mostly from the plasma cosmology thread.

• Magnetic Reconnection Redux VI
• Magnetic Reconnection Redux V
• Reconnection is not induction
• Magnetic Reconnection Redux IV

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From V

Tim Thompson said:

"This is the basic equation of magnetic behavior in MHD, and it determines B once v is known. In the electromagnetic theory of fixed conductors, the electric field and electric current are primary variables with the current driven by electric fields. in such a fixed system the magnetic field is a secondary variable derived from the currents. However, in MHD the basic physics is quite different, since the plasma velocity (v) and magnetic field (B) are the primary variables, determined by the induction equation and the equation of motion, while the resulting current density (j) and electric field (E) are secondary and may be deduced from equations (1.8) and (1.10a) if required (Parker, 1996)."
Priest & Forbes, page 14.
​

The conversion of magnetic energy into a current always operates on a time-scale characteristic of the system, and that time scale is controlled by the ability of the magnetic field to move through the conductor, in order to create a dB/dt term from which the current is generated. That time-scale in a plasma is rather different than it is for a fixed conductor. Here we find the real deal once again in Priest & Forbes:

​

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brantc said:

My question would be "Would a PIC simulation be more "realistic" than a MHD approximation"? Are frozen in fields an artifact of the MHD approximation?

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What should a PIC simulation be more "realistic" than using the ideal MHD equations?
What do you mean by more "realistic"?

Frozen fields are an assumption of the ideal MHD model, i.e. that the topology of the magnetic field is fixed within the fluid.

Reality Check said:

What should a PIC simulation be more "realistic" than using the ideal MHD equations?
What do you mean by more "realistic"?

Frozen fields are an assumption of the ideal MHD model, i.e. that the topology of the magnetic field is fixed within the fluid.

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Somebody said to me:

"MHD is 'smoothed out' plasma, that is, the treatment of plasma physics as fluids. There are no particle physics, electrons and ions, nor is there the concomitant radiation. Instabilities in fluids are well known, but have you ever seen them 'reconnect'?"


And well for instance, why not simulate a laser shot with MHD?

High Performance 3D PIC Code VLPL:Virtual Laser Plasma Lab
"The underlying physics is essentially kinetic and strongly nonlinear, thus precluding the use of hydrodynamic plasma models and/or raxial/quasistatic description of the laser pulse [12]. In this situation one is forced to use fully kinetic description of the plasma.
The most powerful tools for simulations of these strongly nonlinear kinetic phenomena are relativistic fully electromagnetic Particle-In-Cell (PIC) codes [13]. The PIC codes are based on fundamental equations for the particles and fields dynamics and provide the most detailed kinetic description of plasmas.
Fortunately, the super-intense laser pulses are extremely short, 100 fs – 1 ps, i.e., only tens to hundreds of laser periods for 1 m radiation wavelength. It is this short pulse duration that makes direct PIC simulations of relativistic laser-plasma interactions feasible. Two-dimensional (2D) PIC simulations have already become “a working horse” in studies of relativistic laser-plasma interactions."
http://www.billingpreis.mpg.de/hbp99/pu4hbp99.pdf

So this code would be ideal for fast events such as reconnection.
And we know that plasma has some resistance. Which means frozen in field should not exist. It is convenient to model it that way in certain situations but I would say for reconnection PIC is the way to go.
I deal with that every day. We have cold cathode gauges that strike a plasma at about 10-^3 down to 10-^6, is all our turbo/drag pump will do. I'm building a diffusion pump that will do 10-^9 with the right fluid. This gauge works by measuring the current flow which means the plasma dissipates power which means it has resistance.
At large enough time scale you can use MHD to estimate certain parameters about plasma for building a plasma device.
But as far as modeling what is really going at the smallest time scales with radiation and everything, PIC is the preferred method.

The problems is that it is computer intensive so I cant just whip out a sim on my desktop. The simulation mentioned in that paper would take a year on a single processor. Beside the code is for Cray.....

brantc said:

Somebody said to me:

"MHD is 'smoothed out' plasma, that is, the treatment of plasma physics as fluids. There are no particle physics, electrons and ions, nor is there the concomitant radiation. Instabilities in fluids are well known, but have you ever seen them 'reconnect'?"

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Someone said to me "Baaa Baaa Baa". So what?


You did not answer:

• What should a PIC simulation be more "realistic" than using the ideal MHD equations?
• What do you mean by more "realistic"?

brantc said:

So this code would be ideal for fast events such as reconnection.

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How fast is a magnetic reconnection event? Are you stating that they all take the same time? What is that time, a second, a year?

brantc said:

And we know that plasma has some resistance. Which means frozen in field should not exist.

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And we know that plasma has some resistance. Which means frozen in field will exist when that resistance is low enough.

Where do Electric Fields Come From?

brantc said:

But the EU viewpoint is that there is a function that provides for electric fields that are not necessarily gravity driven.

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And what function is that? You can't just invent a function out of your imagination without some basis in physics. I only know of two ways to get an electric field. One of those is through the motion of a magnetic field relative to an electric charge (which will create an effective electric field as far as the charge is concerned), or to physically separate electrically charged particles of opposite sign, so that an electric field appears between the separated charges. If you know of some other way, I am all ears.

"Gravity driven" motions in a plasma are usually not very important. More important are systematic motions (such as those induced by rotation) or turbulent motions induced by thermal effects. These systematic motions will create a relative velocity between charges and therefore generate a magnetic field, which can in turn generate an electric field by motion relative to the charges. But such motions are ineffective at creating bulk charge separation.

brantc said:

These electric fields provide that potential across plasma clouds or from the sun to form a flux tube whos job it is to equalize that potential.

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So my problem is this: Where do these electric fields come from? As far as I can see, you are just inventing them out of "thin air".

Mhd & pic

brantc said:

Isn't that an example of Newtonian thinking?

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Certainly not! Must it not always be true of all mathematical models that they must be consistent with observation? That's all I am really saying.

brantc said:

My question would be "Would a PIC simulation be more "realistic" than a MHD approximation"?

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Just consider ocean water. Do I really need to know anything about the molecular nature of water to understand the dynamics of ocean waves? No, I need only consider the bulk properties of fluid water. But I do need to understand the molecular nature of water to explore surface tension, and that in turn affects how water gets into the air from the ocean. So whether or not I need to look at a kinetic model, that concentrates on the particle nature of water, or a fluid flow model that ignores particles and looks only at continuum properties, depends entirely on the specific problem at hand. Generally speaking, if the problem is large scale & macroscopic, the fluid model will do, but if the problem is small scale & microscopic, then a kinetic model is required.

The same is true for plasma. If you are considering a large scale, macroscopic phenomenon, it is not even possible to use a kinetic model (unless you know how to solve 10²³ simultaneous equations in 10²³ unknowns). So an MHD model is not only appropriate, is is simply the only thing you can ever do. On the other hand, if you are looking at a small scale, microscopic system (like the effect of the presence of the wall of a plasma chamber) then a kinetic model is really required.

I keep making reference to text books on plasma physics because sooner or later the discussion board format becomes inappropriate. Some questions just don't have simple answers and it really is necessary to hit the books and appreciate the genuinely complex nature of things. This is a case in point. Nobody can answer a question like the one you ask because it is too vague & too general.

brantc said:

Are frozen in fields an artifact of the MHD approximation?

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Absolutely not!! an "artifact" is an artificial effect that comes from the mathematics but has no physical reality associated with it. In image processing, for instance, one can easily create "artifacts", which are not really there in the real image, but are there in the processed image. Frozen fields, on the other hand, are very physical and very real, and will manifest themselves in either type of plasma model if you do the physics right. Remember that an MHD model is the approximation to what you would get if you could solve 10²³ simultaneous equations in 10²³ unknowns. The collective energy of the particles is a physically real thing, just as the energy density of the field is a physically real thing. It should come as no surprise to anyone that the larger energy density usually rules the plasma.

Magnetic Reconnection Is Real

From the Michael Mozina's thread on Dark Matter, Inflation and Cosmology.

Michael Mozina said:

The "physics" lesson I am going to teach you personally is related to "induction/circuit reconnection" which you keep describing as "magnetic reconnection" Tim. Let's see you respond to Alfven's first paper please. Notice that part where he describes the amount of current flow in terms of Curl H(B)?

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In a word, no. You keep asking people if they have read Alfven, and they keep answering you, and you just repeat the question as if it had never been asked. It's really annoying, and quite frankly, I've had enough. I answered you already and here is the answer I gave:

Tim Thompson said:

You have asked this question about a bazillion times, keep getting the same answers, and then just ask it again like it's the first time. How many times do I have to tell you ... YES ... I have read the book and I have two copies of it in my physics library. I used the book as a reference when I was a graduate student.

So, how about a show of hands from Michael Mozina:
Have you read Magnetic Reconnection: MHD Theory and Practice by Priest & Forbes?
Have you read Nonlinear Magnetohydrodynamics by Deiter Biskamp?
Have you read Fundamentals of Plasma Physics by Paul Bellan?
Have you read The Physics of Plasmas by T.J.M. Boyd & J.J. Sanderson?
Have you read Plasma Physics for Astrophysics by Russell Kulsrud?
Have you read Plasma Astrophysics by Toshiki Tajima & Kazunari Shibata?
Have you read Conversations on Electric and Magnetic Fields in the Cosmos by Eugene Parker?

If you have not read any of these, can you tell us what plasma physics books, other than Alfven, you actually have read?
How many plasma physics classes have you taken?
How many plasma physics laboratory experiments have you performed yourself, or assisted with?

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I will not discuss magnetic reconnection with you at all until you answer everything from the post I quoted above.

Even then, I refuse to consider anything from Alfven, neither paper nor book. You act as if physics came to a screeching halt with Alfven and totally ignore everything and everyone who has studied electromagnetism since then. You treat Alfven as if he were God himself, totally incapable of being even the slightest bit wrong about anything. And you always ignore the real physics of every situation.

Enough with the constant refrain of "circuit reconnection" and "particle reconnection", it's time to do real physics. If you think that real magnetic reconnection is really wrong, then prove it. Don't just say it, and don't tell us that "Alfven said so". I don't care what Alfven said because I already know he was wrong. If you can't point out specifically where any of the sources I list above are wrong, if you can't show where the physics is wrong, then you have nothing at all to teach anyone.

Michael Mozina said:

I'm going to have to nibble at your posts after work Tim, but your notion of "magnetic reconnection' being a unique form of energy exchange is going down.....

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Crackpot standard operating procedure: start with the conclusion, then say anything you can make up to try and support it.

Michael Mozina said:

It's a "short circuit" between two current carrying "magnetic ropes". Is that clear enough?

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I think that is clearly not clear enough.

• What is a "short circuit" and how does it differ from a short circuit or the merging of two electric currents?
• What are "magnetic ropes" and how they differ from say magnetic flux.
• How do the "magnetic ropes" ropes carry current?
• What is the mathematical relationship between the properties of the "magnetic ropes" and the current that they carry?
• Where does the energy come from in the "short circuit" that is detected in magnetic reconnection?
• How much energy is released in the "short circuit" and how does that compare to the energy that is detected in magnetic reconnection?

You may find it easier to just cite the textbook from which you learned this concept of "circuit reconnection".

Fields: Points & Lines

Zeuzzz said:

Thanks tim, but if you could answer each of the questions in the OP I think that would resolve any issues far quicker than your long posts summarizing the theory.

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I don't think I can do a better job than the answers you already rejected. Rather, I think your reasons for rejecting the answers you already have are not good. Let me concentrate on the issue of field lines.

Zeuzzz said:

Every magnetic field is a continuum, i.e., a vector field. Each of the infinite and uncountable points in this continuum has a magnitude and a direction that is associated with it. This continuum is not made of (does not contain) a set of discrete lines. Lines can be drawn on paper to describe the magnetic fields direction and magnitude, however the field itself is not made of these lines.

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It is not obvious that this is correct. Consider this:

sol invictus said:

One can fully characterize the field by its lines - in the limit of infinite line density, all the information about the field is contained in the line configuration.

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It makes no difference. You can't say that lines are wrong and points are right as both tell us exactly the same thing.
And consider this:
The lines constitute a 1+1 dimensional field embedded in a 3+1 dimensional field. It is critical to note from the comments by Ashok Das that this includes moving lines. We assume that the field is a physical entity unto itself (as Maxwell makes explicit in his 1861 paper On Physical Lines of Force). But points and lines are only mathematical methods of describing the behavior of the field. We do not know what the field "really is" nor do we know what the field is "really made of". All we know is that we can describe the physical phenomena associated with the field through some mathematical methodology. The physical reality of the lines is no more relevant than the physical reality of the points; both are in fact mathematical entities and neither is necessarily physical. It is (and indeed it must be) the case that describing changes in the field makes just as much sense using the formalism of moving lines as it does to use any other mathematically & physically correct formalism. Just look at any textbook on electromagnetism and you will find that not only are moving lines perfectly reasonable, but likely the easiest way to characterize the field.

The Man said:

MM, take a couple of refrigerator magnets (the flat rectangular business card or credit card company types), they have alternating north south stripes (generally running vertically). If you place two back to back and slide them across each other you will feel those magnetic stripes alternately repelling and attracting each other. When you feel it switching from resisting the sliding to that sliding being easier (and being pulled in that direction) that is magnetic reconnection as field lines from the stripes on one refrigerator magnet reconnect to the next stripes on the other refrigerator magnet. No “magic magnets”, just what magnets do and reconnection that you can experience in your own kitchen or home. You could do the same thing with a compass and a magnet, the compass needle being itself a small magnet. When the magnet is far from the compass the needle is connected to the earths magnetic field as you bring the magnet closer to the compass at some point the felid of the needle reconnects to that of the magnet and the compass points at the magnet. Move the magnet away from the compass and the field of the needle will reconnect to the magnetic field of the earth. Repeat as many times as you feel necessary until you stop believing in "magic magnets".

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Quoted here for possible disscussion

Fields: Points & Lines II

I want to take another crack at the concept of field lines. One of the complaints leveled at the idea of magnetic reconnection is that the field lines are not physically real, which I think is an irrelevant point. So it does not hurt to consider for a moment exactly what a "field line" is supposed to be in some detail.

What is a "field line"?
The concept for "lines of magnetic force" comes from Michael Faraday and was adopted by Maxwell (see On Faraday's Lines of Force; page 155 in the same volume I of Maxwell's collected papers; read Dec 10, 1855 and Feb 11, 1856). He later generalized the concept and used it to literally invent the theory of electromagnetic fields, and really the general topic of field theory (see A Dynamical Theory of the Electromagnetic Field; page 526 in the same volume I of Maxwell's collected papers; read Dec 8, 1864; and see the subsection On Lines of Magnetic Force, page 551 and On Magnetic Equipotential Surfaces, page 553). In the passage above, where Maxwell begins "We are dissatisfied ...", he is expressing his dissatisfaction with the notion of "action at a distance" (an idea Newton did not like either), and his belief that some "physical state or action" must permeate the space around the magnet. That "physical state or action" of 1861 became Maxwell's electromagnetic field of 1864.

At this point it is critical to understand the proper relationship between physics & mathematics. Mozina has repeatedly complained that "the math is right" for magnetic reconnection, but the physics is all wrong. But that makes no sense at all, because math & physics are really the same thing! The real distinction should not be between mathematics & physics, but rather between theory and observation. Assuming we make no mistakes (at least no serious mistakes), then we can rest assured that observation is the real thing, a true chronicle of the way the universe really behaves. Our theory, on the other hand, is our explanation for why we think observation comes out the way it does. Mathematics is the language we use to construct the theory, and the tool we use to explore the ramifications of theory. We do require that the ramifications & predictions of theory do not seriously conflict with observations (small differences we can & do live with, big differences could be fatal to a theory).

Field lines of any kind are mathematical entities and whether or not they are "physically real" is not relevant (how would you actually prove conclusively one way or the other anyway?). It only matters that the observed behavior of the electromagnetic field is consistent with the implied behavior of the electromagnetic field, given a mathematical formalism based on the concept of field lines. This is in fact the case, as Maxwell carefully pointed out in 1864, and there is no instance of fact that I am aware of since then which implies the contrary. The formalism of field lines precisely replicates the observed behavior of the electromagnetic field.

So let me return to a previous comment:

Tim Thompson said:

What is magnetic reconnection?
My authoritative source for the physics of magnetic reconnection is the book Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes, Cambridge University Press, 2000. Let me quote from the introduction (page 1): "As we shall discuss in more detail later on, reconnection is essentially a topological restructuring of a magnetic field caused by a change in the connectivity of its field lines." And in the following paragraph we find this: "The evidence of reconnection in laboratory fusion machines such as the tokamak and the reversed field pinch is so strong that there is no longer any controversy about whether reconnection occurs, but only controversy about the way in which it occurs."

Click to expand...

Now, the mathematical formalism which describes the behavior of the magnetic field is the reconnection of mathematical field lines, hence the title "magnetic reconnection". It does not matter at all that the lines may or may not be themselves physically real. What does matter is that the mathematical formalism and the observed behavior of the field are mutually consistent, and they are in fact so. It also matters that magnetic reconnection and induction are easily distinguished, one from the other, as I have already pointed out for the relevant case of solar plasma physics:

Tim Thompson said:

Why not induction?
Now, Mozina insists that what we are really seeing is induction. Is this a reasonable assertion? At the level of real physics it appears to be unrealistic. We know that induction is invariably constrained (or unconstrained) by the characteristic diffusion time for the magnetic field in a given environment. Remember that in the process of induction, the magnetic field move with respect to the charged particles, and it is that relative motion between field & particle that determines the transfer of energy from the magnetic field to the particles. Let me quote once again from Priest & Forbes, this time from section 1.1 ("The Origins of Reconnection Theory"), pages 6-7: "For example, solar flares release stored magnetic energy in the corona within a period of 100 s. By comparison, the time-scale for magnetic dissipation based on a global scale length of 10⁵ km is of the order of 10⁶ yrs. Typically, phenomena like the solar flare and the substorm require a significant fraction of the stored magnetic energy to be converted within a few Alfven time-scales. Such rapid time-scales are easily achieved in ideal MHD processes, but not in non-ideal ones. Although ideal MHD processes can release energy quickly, they rarely release a significant amount because of the topological constraints which exist in the absence of dissipation. In contrast, magnetic reconnection is not topologically constrained, and therefore it can release much greater amounts of energy (Kivelson and Russell, 1995)."

Click to expand...

The best Mozina could come up with in answer to this was simply ...

Michael Mozina said:

Let's look at your silly quote, one that is *EASILY* debunked. ... None of you have ever seen a "coil" in action eh?

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That's the extent of Mozina's depth when it comes to thinking about physics. Of course, he had to completely ignore this:

Tim Thompson said:

"This is the basic equation of magnetic behavior in MHD, and it determines B once v is known. In the electromagnetic theory of fixed conductors, the electric field and electric current are primary variables with the current driven by electric fields. in such a fixed system the magnetic field is a secondary variable derived from the currents. However, in MHD the basic physics is quite different, since the plasma velocity (v) and magnetic field (B) are the primary variables, determined by the induction equation and the equation of motion, while the resulting current density (j) and electric field (E) are secondary and may be deduced from equations (1.8) and (1.10a) if required (Parker, 1996)."
Priest & Forbes, page 14.

Click to expand...

Evidently Mozina has yet to figure out that coils & plasmas are not exactly the same thing.

In any case, there are some important points to take away from all this:

• Whether or not field lines are physically real is irrelevant.
• The mathematical theory of field lines accurately reconstructs observed physics.
• Magnetic reconnection and induction are easily distinguished. Despite claims to the contrary, modern physicists are not collectively making such an obvious mistake.

PDF copies of Maxwell's papers On Physical Lines of Force and A Dynamical Theory of the Electromagnetic Field are available on the Wikipedia page A Dynamical Theory of the Electromagnetic Field.

Hi Tim,

Thanks for the history lesson.

How do you explain the reconnection rate being able to be set arbitrarily and, if you could, kindly explain the physical mechanism associated with the energy released.

Zeuzzz said:

Hi Tim,

Thanks for the history lesson.

How do you explain the reconnection rate being able to be set arbitrarily and, if you could, kindly explain the physical mechanism associated with the energy released.

Click to expand...

Hi Zeuzzz,
I think that Tim would like a source for your assertion that the reconnection rate is set arbitarily in MHS simulations. A quick look suggests that reconnection rates emerge from the simulations, i.e. model parameters are set, the simulation is run and one thing you get out are reconnection rates.
For example this 1994 paper: What is the condition for fast magnetic reconnection?

The magnetic reconnection driven by magnetic buoyancy instability is studied using two-dimensional MHD simulations for two resistivity models; uniform resistivity, and anomalous resistivity. It is found that the reconnection rate is not uniquely determined by the driving process but strongly dependent on the resistivity model, i.e., the local plasma condition near the neutral point. The uniform resistivity case becomes steady Sweet-Parker type, while the anomalous resistivity case tends to nonsteady Petschek type. In the latter case, the reconnection rate increases with increasing threshold of anomalous resistivity. The formation of magnetic islands (plasmoids) and their subsequent ejection from the current sheet is found to be a key physical process leading to fast reconnection.

Click to expand...

You may also want to specify more exactly what you mean by "physical mechanism".
It seems simple enough to me - the magnetic energy of the magnetic fields heats up the plasma when the magnetic field changes. But it is probably more complex than that.

Reality Check said:

You may also want to specify more exactly what you mean by "physical mechanism".
It seems simple enough to me - the magnetic energy of the magnetic fields heats up the plasma when the magnetic field changes. But it is probably more complex than that.

Click to expand...

You have to explain where the magnetic field gets its instantaneous energy from. The law of physics that I use is that moving electron(in the same direction) will make a magnetic field. A flux tube has many different motions of particles. Some are circular and some are completely parallel. Thats how you get that particular type of configuration.
The change is gyroradius leads to a change in the forces between the tubes and they touch and a burst of particles comes out(accelerated ions and electrons). They reform and the process happens again. Especially in the case of the Earths magnetotail. It has a line of reconnection events that extend across the daylight line?

To get to the bottom of this it is going to take a little more time to explain why doing a Particle in Cell simulation is going to be more informative than a MHD simulation.

I can already tell you one thing. Turbulence is a fluid term. That doesnt happen in plasma. Turbulence is driven from the top down(pipe wall etc.).
EM (PIC) is driven from the particle up by instabilities..
Instabilities might look the same as turbulence but they are quite different.

But it seems as though somebody is already doing a major experiment with PIC code and reconnection at the LAPD device.. Why dont they just use MHD code?

Current-driven turbulence, anomalous resistivity and particle energization
<snip>
While evidence is now substantial that anomalous resistivity may be active during reconnection, we are far from having a comprehensive understanding of the detailed mechanisms sufficient to model the effect in nearly collisionless systems such as tokamaks where reconnection electric fields can exceed the Dreicer runaway field during sawteeth and disruptions.
To address this question we propose a program with three linked elements. The first is a comprehensive set of laboratory experiments to be carried out on the LAPD device at UCLA to explore the development of electron-ion streaming instabilities and associated heating and anomalous resistivity. The second element is turbulence measurements during reconnection on VTF at MIT. In the third element, parallel 3-D particle simulations with the p3d code will be carried out and the results compared with the experimental measurements. The relative roles of the ion acoustic instability, which can be driven unstable when Te >> Ti, the Buneman instability and off-angle lower-hybrid modes will be explored. Questions such as the following will be addressed.
</snip>
http://www.cscamm.umd.edu/cmpd/anomalous.htm

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Here is my prediction.

They will find that the plasma in the reactor reaches a certain energy level(temperature) and the sheath between the wall and the plasma breaks down.
This leads to a discharge(current flow) to the wall that has a pinch in it that emits xrays etc.

They kind of already know this but they don't say it so simply.

Reconnection Rates

Zeuzzz said:

How do you explain the reconnection rate being able to be set arbitrarily ...

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I don't know what you mean here, unless as RC notes, you think the reconnection rates are arbitrarily set in simulations. I would need to see a specific case to know. However, in general, the reconnection rate depends on the magnetic Reynolds number of the plasma. If you run a simulation where you know the magnetic Reynolds number for the plasma, then you should be able to set the reconnection rate arbitrarily, depending on what the simulation is supposed to do (reconnection rates are covered in detail in Magnetic Reconnection by Priest & Forbes).

Zeuzzz said:

... and, if you could, kindly explain the physical mechanism associated with the energy released.

Click to expand...

Easy. Like everything else in the universe, magnetic fields have an intrinsic internal energy, and like everything else in the universe, magnetic fields seek the lowest energy state as spontaneously as they can. Magnetic reconnection is nothing more complicated than a change in the topology of the magnetic field, from a higher energy state to a lower energy state. The energy lost is transferred, probably by magnetosonic waves, to the plasma.

Cant reply in full atm but

Tim Thompson said:

Magnetic reconnection is nothing more complicated than a change in the topology of the magnetic field, from a higher energy state to a lower energy state. The energy lost is transferred, probably by magnetosonic waves, to the plasma.

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That sentence seems to be slightly confusing.

I'd have said it more like;

Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use (like contour lines) to represent magnetic fields, from a higher energy state to a lower energy state. Some people think that the field lines we plot to represent them do actually exist and can have real world effects. Some people believe this a theory based on reified components and thus is false. Magnetic field lines can not move independantly. Just like contour lines can not interact. They do one job, and one job only: describe the field strength on a vector field they are modelling.

Zeuzzz said:

Cant reply in full atm but



That sentence seems to be slightly confusing.

I'd have said it more like;

Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use (like contour lines) to represent magnetic fields, from a higher energy state to a lower energy state. Some people think that the field lines we plot to represent them do actually exist and can have real world effects. Some people believe this a theory based on reified components and thus is false. Magnetic field lines can not move independantly. Just like contour lines can not interact. They do one job, and one job only: describe the field strength on a vector field they are modelling.

Click to expand...

As that vector field changes so do the field lines we use to represent it or portions of it. The specific representation is not as important as the reconfiguring (changes in magnitude and direction) in that vector field. The use of the field lines in that representation helps to more easily understand how that reconfiguring progresses in the area of concern.


ETA:

Vectors are also just lines we use to represent magnitude and direction, however field lines give a more intuitive and easily discernable representation of that topography (and more specifically the changes) rather than perhaps a blur of redirecting waxing and waning vector lines.

brantc said:

You have to explain where the magnetic field gets its instantaneous energy from. ...snip....

Click to expand...

The magnetic field gets its "instantaneous energy" from the energy stored in the magnetic field. It is basic electromagnetism that magnetic fields contain energy.
Where the magnetic field gets the energy that is stored in it depends on what creates the magnetic field. For example:

• In the magnetic reconnection experiments in labs, from the electric currents running through the magnets.
• In the Earth's magnetosphere, from the origin of the Sun's magnetic field (thought to be from the motion of plasma in the Sun).
• In solar flares, usually from the creation of coronal loops within the solar body before they well up through the photosphere.

Zeuzzz said:

I'd have said it more like;

Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use (like contour lines) to represent magnetic fields, from a higher energy state to a lower energy state. Some people think that the field lines we plot to represent them do actually exist and can have real world effects. Some people believe this a theory based on reified components and thus is false. Magnetic field lines can not move independantly. Just like contour lines can not interact. They do one job, and one job only: describe the field strength on a vector field they are modelling.

Click to expand...

Obviously you did not read Tim Thompson's post just above yours: Fields: Points & Lines II

I'd have said it more like:
Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use to represent magnetic fields, from a higher energy state to a lower energy state. The energy lost is transferred, probably by magnetosonic waves, to the plasma.

And some stuff not about magnetic reconnection at all:
Some confused people think that the field lines we plot to represent magnetic fields do actually exist physically. Magnetic field lines represent the magnetic fields and so changes in the them (and so the magnetic field) will have real world effects. Magnetic field lines can not move independently. Just like contour lines can not interact. They do one job, and one job only: describe the field strength on a vector field they are modeling.

Reality Check said:

I'd have said it more like:
Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use to represent magnetic fields, from a higher energy state to a lower energy state. The energy lost is transferred, probably by magnetosonic waves, to the plasma.

Click to expand...

Well I only pop back for a second and already you have given some prime examples of fundamental issues with magnetic reconnection.

No wonder even experts in this field tend to agree that there are a lot of ambiguities in the theories involved. For example what distinguishes magnetic reconnection from current disruption if they are both derived from different (but equivalent) versions of maxwells equations.

Its brilliant. Once one bit clicks the rest will to.

Now lets consider your sentence, Magnetic reconnection is nothing more complicated than a geometric change in the topology of the lines we use to represent magnetic fields, from a higher energy state to a lower energy state. The energy lost is transferred, probably by magnetosonic waves, to the plasma.

You know whats wrong with this sentence?

None of it exists. Thus none of it can be proven.

so,

Magnetic reconnection = The process = Metaphysical
Geometric change = (unspecified) = Metaphysical
Topology of the lines = (unspecified, around a neutral point?) = Metaphysical
Magnetic fields = Metaphysical (as a secondary effect they can interact with material things)
Magnetic field lines = Metaphysical
High Energy State = Metaphysical
Low Energy State = Metaphysical

I suppose that unprovable "Collisionless reconnection" will be the next property to add to the list as the theory gets forever more complex.

Great! We're nearly at the stage where an entire theory can be created out of metaphysics, and people will believe their theories even if reality shows something else.

Coz reality must be wrong, eh? Coz that theories so well established now that it cant be, people would have stopped to double check its veracity surely? ... Oh yea, they did. Alfven et al were mostly staunchly opposed to magnetic reconnection as are many others.

This is what happens when people start to reify maths and concepts, you can end up making perfect theories that look right but are completely devoid of reality. The one possible testable physical link that makes the theory make sense is based on interactions due to a not real object, a re-ified magnetic field line. On paper it will work out fine everytime, but often the universe has other ideas.

Would be similar to einstein saying that you could not dig directly through the earth as you would literally bump into the Earths COG and stop. You of course wont bump into the COG irrespective of what the 'tensions' or mathematical abstractions were previously assigned to it, the COG exists only in our heads! There is a physical core to the planet in the same sort of area as the COG, which can have absolutely no physical effect on anything. Like a magnetic field line.

Now I left one thing out,

magnetosonic waves, to the plasma > Is this relevant to any real world things or tests?


You see drop the Bu approach and use the Ej and you have magnetic reconnections identical twin, current disruption. Which unlike MR can be tied down to particle collisions and real world events. Much nicer.

Zeuzzz said:

Well I only pop back for a second and already you have given some prime examples of fundamental issues with magnetic reconnection.
...snip....

Click to expand...

Well I only pop back for a second and already you have given some prime examples of being wrong.

The fact that magnetic fields contain energy is basic electromagnetics. I suggest that you look it up.

Magnetic reconnection = The process = physical
Geometric change = the change in the magnetic field = physical
Topology of the lines = the magnetic field = physical
Magnetic fields = physical
Magnetic field lines = physical
High Energy State = physical
Low Energy State = physical

Zeuzzz said:

magnetosonic waves, to the plasma > Is this relevant to any real world things or tests?

Click to expand...

Yes: Magnetosonic wave

Zeuzzz said:

You see drop the Bu approach and use the Ej and you have magnetic reconnections identical twin, current disruption. Which unlike MR can be tied down to particle collisions and real world events. Much nicer.

Click to expand...

That displays the sillinees of your post beause I can say

Magnetic reconnection = The process = Metaphysical
Geometric change in electric field = (unspecified) = Metaphysical
Topology of the electric field lines = (unspecified, around a neutral point?) = Metaphysical
Electric fields = Metaphysical (as a secondary effect they can interact with material things)
Eleactic field lines = Metaphysical
High Energy State = Metaphysical
Low Energy State = Metaphysical

Great! We're nearly at the stage where an entire theory can be created out of metaphysics, and people will believe their theories even if reality shows something else.

Click to expand...

Source for your assertion that magnetic reconnection = currrent disruption

Zeuzzz said:

You see drop the Bu approach and use the Ej and you have magnetic reconnections identical twin, current disruption. Which unlike MR can be tied down to particle collisions and real world events. Much nicer.

Click to expand...

First asked 28 January 2010
Zeuzzz,
What is the source for your assertion that magnetic reconnection is identical to current disruption?

You can start by citing the definition of "current disruption" from a textbook.

Then show that current disruption in a plasma

1. Releases the same amount of energy as magnetic reconnection.
2. Releases that energy at the same rate as magnetic reconnection.

brantc said:

You have to explain where the magnetic field gets its instantaneous energy from. The law of physics that I use is that moving electron(in the same direction) will make a magnetic field. A flux tube has many different motions of particles. Some are circular and some are completely parallel. Thats how you get that particular type of configuration.

Click to expand...

Well then your physics is wrong, in a flux tube the particles (that are magnetized) are traveling along the field gyrating around the field lines.
Particle moving along the field line cannot generate the large scale field that they are traveling along. There is a source somewhere that generates the flux tube.

Now naturally it depends a bit on what object you look at. If you look at the sun then the fields are generated under the surface, if you look at the solar wind, there can be "self contained" magnetic cloud, however these dissipate rather quickly because there is no longer a driving force for the current.

You might want to calculate what amount of "circular" orbits it would take to create the core field of a flux tube, and then see whether that it compatible with the densities etc. that are measured.

brantc said:

The change is gyroradius leads to a change in the forces between the tubes and they touch and a burst of particles comes out(accelerated ions and electrons). They reform and the process happens again. Especially in the case of the Earths magnetotail. It has a line of reconnection events that extend across the daylight line?

Click to expand...

What change in gyroradius are you talking about? What forces between the tubes, do you have two tubes interacting, or what?
I assume then you have two tubes and "they touch". How do they touch? Why would the change in gyro radius do this, what is the gyro radius of the ions and electrons? Qualify your ideas please, otherwise it's just statements that don't make any sense.

In the case of the Earth's magnetotail you have oppositely directed field separated by a cross-tail current (in which direction is the current flowing?)
The tail does not have a "line of reconnection events" and it most definitely does not "extend across the daylight line. Reconnection in the tail happens at 15 - 25 Earth radii down the tail, there can be a broad region across the tail (i.e. east-west) where reconnection happens (the associeated flows are approximately 2 to 3 Earth radii wide Nakamura et al. 2004), which is what is called the reconnection line, as opposed that it happens in a "point."

So please get your facts right before you answer again.

brantc said:

I can already tell you one thing. Turbulence is a fluid term. That doesnt happen in plasma. Turbulence is driven from the top down(pipe wall etc.).
EM (PIC) is driven from the particle up by instabilities..
Instabilities might look the same as turbulence but they are quite different.

Click to expand...

What kind of utter nonsense is this! Plasmas are prone to loads of instabilities and waves. Indeed, not all instabilities will lead to turbulence, e.g. good old Alfvén's double layers are created by an instability but are not turbulent. However the electron beam coming out of a strong (relativistic) double layer will most definitely drive a beam-plasma instability, producing waves that lead to turbulence.

Turbulence is the cascade of wave energy from large to small scales which has been observed e.g. in the Earth's magnetotail as presented by:
volwerk et al. 2004 Multi-scale analysis of turbulence in the Earth's current sheet
Vörös et al. 2005 Magnetic turbulence in the plasma sheet
Vörös et al. 2005 Dissipation scales in the Earth's plasma sheet estimated from Cluster measurements
Vörös et al. 20066 Bursty Bulk Flow Driven Turbulence in the Earth's Plasma Sheet
Vörös et al. 2007 Spatial structure of plasma flow associated turbulence in the Earth's plasma sheet
Vörös et al. 2007 Spectral scaling in the turbulent Earth's plasma sheet revisited
Vörös et al. 2008 Study of reconnection-associated multiscale fluctuations with Cluster and Double Star
2008 Magnetic fluctuations and turbulence in the Venus magnetosheath and wake

And that is just a short list of papers from my friend Zoltan and me.

tusenfem said:

Well then your physics is wrong, in a flux tube the particles (that are magnetized) are traveling along the field gyrating around the field lines.

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Let's talk physics. When you say "flux tube", are you talking about an ordinary plasma filament like we find in a ordinary plasma ball, simply scaled to some larger size?

What PHYSICAL PARTICLES are inside that "flux tube"?