Magnetic reconnection and physical processes

[brantc]

Try to understand what you read.

1. The currents merge and split in space and time.
2. are peppered with regions in which magnetic fields that point in opposite directions are forced together
3. The data indicate that they [the regions in the previous sentence] are likely the sites of magnetic field-line reconnection.

That is basic to magnetic reconnection in plasma. The sites of magnetic reconnection have currents around them which maintain the neutrality of the plasma.

This of course has nothing to do with what I posted.

The kinetic energy of the particles in the current cannot account for the magnitude and time scales of observed magnetic reconnetion. This has also pointed out in many previous posts.

Is what you posted.

I posted the laser produced plasma to show you that indeed the kinetic energy of the particles in the laboratory is responsible for the plasma filled flux tubes.
Multiple reconnections on the same current channel within 2 mircoseconds.

It probably started at one end and progressed down to the other end.

First asked 21 February 2010
brantc,
What is the energy released from the kinetic energy of the currents?

You mean how strong is the magnetic field from the kinetic energy of the electrons(current) flowing through it?
Just measure the magnetic field and that will tell you the strength of the current flow through the channel(Ampere's Law).
However that doesn't tel you the peak available current, only what is being drawn for the local process of supporting the loop.

How does this energy compare to the energy released in magnetic reconnection?

When doing a z-pinch experiment you need to have capacitors that will store twice as much as your plasma discharge will use.

So in the case of a reconnection attached to the solar surface, the whole of the sun is available to power it, or the energy of the battery or capacitor attached to the circuit.
I would be surprised if you didnt accept this as enough power for any locally observed reconnection.

This should be an easy question to answer sonce there must be 100's of papers on the subject many of which you have read to form your conclusion.

Yep. Heres one.
Exploring the Secrets of the Aurora
Chapter 5
Myth of the Emerging flux tubes:Sunspots and Solar flares.
Check out the 3 step hypothesis part 5.2 page 149.

http://books.google.com/books?id=uh...resnum=7&ved=0CCIQ6AEwBg#v=onepage&q=&f=false

 

[brantc]

Tim Thompson's comments is quite correct.
If you are not interested in the positions or velocities of individual particles in a system containing a large number of particles then treating the system as continuous is the way to go. It would be ridiculous to try to model waves in an ocean using the the particles in it (10^23 molecules in 1 mole of water!). Thus MHD is valid for many plasmas.

How do you know what your are interested in?

MHD is valid for many plasmas, it just happens to be failing in this particular situation.

If your simulations fail then its time to move to the next level of detail like PIC.

Isnt that the difference? The level of detail that you get back?
The correctness of the model is based on the level of detail.

 

[Reality Check]

Citations for kinetic energy is the primary source in magnetic reconnection

I posted the laser produced plasma to show you that indeed the kinetic energy of the particles in the laboratory is responsible for the plasma filled flux tubes.

You really need to understand what you read. I will make it clearer :


The kinetic energy of the particles in the current cannot account for

• The size of the eneragy released in the magnetic reconneciton.
• The time that the magnetic reconnection takes.

This has also pointed out in previous posts. Tim Thompsons posts are good, e.g. Magnetic Reconnection Redux VII

So lets look at the laser experiment that you are obsessed with one more time
Visualizing Three-Dimensional Reconnection in a Colliding Laser Plasma Experiment

Most processes in nature where magnetic field line reconnection occurs are thought to be 3-D and time dependent. These include solar flares and sites in the Earth’s and in Jupiter’s

magnetotails, as well as astronomical objects such as pulsars and colliding galaxies. We present experimental evidence for a fully 3-D reconnection, which occurs when two dense plasmas collide in a background-magnetized plasma.

You are not understanding the paper.

• There is no calculation of the kinetic energy in the colliding plasma.
• There is not even a calculation of the energy released in the magnetic reconnection from the magnetic field.

Strangely enough Visualizing Three-Dimensional Reconnection in a Colliding Laser Plasma Experiment is about Visualizing Three-Dimensional Reconnection in a Colliding Laser Plasma Experiment !

You mean how strong is the magnetic field from the kinetic energy of the electrons(current) flowing through it?

No - energy means energy.

So in the case of a reconnection attached to the solar surface, the whole of the sun is available to power it, or the energy of the battery or capacitor attached to the circuit.
I would be surprised if you didnt accept this as enough power for any locally observed reconnection.

brantc, posted by Tim Thompson:

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)."

Emphasis added.
The only kinetic energy that is available to the flare is from particles that can get to the release point in 100 seconds.
On the other hand all of the energy in the magnetic field is available to be released in the flare (subject to light speed of course). The magnetic field of a solar flare has a large volume (1000's of cubic kilometers? at a guess) and a non-zero energy density.
So be surprised - the physics states you are wrong !

Yep. Heres one.

Nice book. No math or actual calculations on what I asked you.

I will restated the previous questions in a hopefully clearer manner:
First asked 21 February 2010
brantc,


What are your citations for your assertion that kinetic energy is the primary source for energy in magnetic reconnection?

1. This should answer the previous 2 questions
   What is the energy released from the kinetic energy of the currents?
2. How does this energy compare to the energy released in magnetic reconnection?

from some of the 100's of papers on the subject, many of which you have read to form your conclusion.

Or are we back to this is some idea of yours with no scientific backup?

 

[Tubbythin]

Science is an entirely human contrived unit!!!

Science isn't a unit.

So what units do you use to characterize an electron when you talk to other scientists????

Depends what I'm talking to them about. If we're talking thermal energies I might use meV, if we're talking rest mass energy I'll almost exclusively use keV, if we're talking the ILC I'd use GeV or TeV. But that doesn't make the eV a fundamental unit. Its a unit of convenience, nothing more. And it has nothing to do with one foot.

 

[Reality Check]

How do you know what your are interested in?

If you are not interested in the individual particles than you are obviously not interested in the individual particles !
Seriously if you are looking at the bulk properties of a system that can be described as a fluid then describe it as a fluid.

MHD is valid for many plasmas, it just happens to be failing in this particular situation.

How doe it fail in this particular situation?

If your simulations fail then its time to move to the next level of detail like PIC.

What simulations failed?

Isnt that the difference? The level of detail that you get back?
The correctness of the model is based on the level of detail.

How do you know that a PIC simulation returns a higher level of detail than a MHD simulation? It could give back a lower level of detail.

 

[tusenfem]

Ok. I was tired when I wrote that.
It is the energy gained by an electron when accelerated by 1 volt across 1 foot. At the end of the acceleration that electron is going to have accelerated by some amount that is equivalent to a velocity.
It gains kinetic energy.

There is no foot in the electron volt. The one volt may be stretched over 1 lightyear and the electron would still only gain 1 eV.

 

[dafydd]

There is no foot in the electron volt. The one volt may be stretched over 1 lightyear and the electron would still only gain 1 eV.

Electron volts have feet,otherwise how would they get around?

 

[brantc]

Science isn't a unit.


Depends what I'm talking to them about. If we're talking thermal energies I might use meV, if we're talking rest mass energy I'll almost exclusively use keV, if we're talking the ILC I'd use GeV or TeV. But that doesn't make the eV a fundamental unit. Its a unit of convenience, nothing more. And it has nothing to do with one foot.

Never mind!

 

[brantc]

There is no foot in the electron volt. The one volt may be stretched over 1 lightyear and the electron would still only gain 1 eV.

Absolutely. I use 1 foot because its convenient in the lab here on earth.
Its still 1 volt.

 

[Ziggurat]

brantc, your understanding of the relationship between energy and velocity appears to have some serious problems. It's true that for a given energy, a given particle will have some particular velocity magnitude (direction doesn't matter) which will have that much kinetic energy. But what that velocity is varies from particle to particle. It's not the same for a proton as it is for an electron, it's not the same for an alpha particle as for a proton, etc. Unlike the relationship between energy and rest mass, it isn't a unique relationship. Furthermore, kinetic energy is only one of MANY forms of energy. If you give me an energy, I could tell you the velocity of an electron with that much energy. But I could also tell you the wavelength of a photon with that energy. Or the number of photons of some fixed wavelength with that energy. Or the separation distance between two charges with that energy. Etc., etc. It just doesn't make any sense to treat kinetic energy as being special in this regard, because it just isn't.

 

[brantc]

brantc, posted by Tim Thompson:

Originally Posted by Tim Thompson View Post
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)."

Emphasis added.
The only kinetic energy that is available to the flare is from particles that can get to the release point in 100 seconds.
On the other hand all of the energy in the magnetic field is available to be released in the flare (subject to light speed of course). The magnetic field of a solar flare has a large volume (1000's of cubic kilometers? at a guess) and a non-zero energy density.
So be surprised - the physics states you are wrong !

You have the energy that is stored in the magnetic field, and the energy available from the flux tubes connected to the solar surface.
This energy is available up to the point of the "null" or particle jets, and then only the energy of the flux tubes is available until the magnetic field builds up again.

This is all from the kinetic energy of the particles.

The moving particles create the magnetic field. When the flow stops(or changes direction) the magnetic field collapses and releases energy.
Reconnection.

There is nothing inconsistent to what I'm saying.
I am following the right hand rule which indicates the magnetic field is produced by moving particles except in the filed aligned case, although there is still a small parallel component in non field aligned currents..

The only thing you might be able to say is that a direct measurement of the particle count and temperature of a flux tube doesnt match the magnetic field.
If so I would like to see that paper.

 

[brantc]

brantc, your understanding of the relationship between energy and velocity appears to have some serious problems. It's true that for a given energy, a given particle will have some particular velocity magnitude (direction doesn't matter) which will have that much kinetic energy. But what that velocity is varies from particle to particle. It's not the same for a proton as it is for an electron, it's not the same for an alpha particle as for a proton, etc. Unlike the relationship between energy and rest mass, it isn't a unique relationship. Furthermore, kinetic energy is only one of MANY forms of energy. If you give me an energy, I could tell you the velocity of an electron with that much energy. But I could also tell you the wavelength of a photon with that energy. Or the number of photons of some fixed wavelength with that energy. Or the separation distance between two charges with that energy. Etc., etc. It just doesn't make any sense to treat kinetic energy as being special in this regard, because it just isn't.

I agree with you that it is not unique. In this instance I use eV when talking about particles and particle energy (besides Joules) because it is a more fundamental quality.

How would you express electron energies in a plasma?? Temperature(bulk) breaks down to eV(particles).

 

[Ziggurat]

How would you express electron energies in a plasma?? Temperature(bulk) breaks down to eV(particles).

I could do that any number of ways. Temperature is just as good a metric as energy, and unlike velocity and energy there IS a unique conversion from one to the other (and not just for plasmas) in the form of Boltzmann's constant k. And if I did it in units of energy, I could use Joules instead, there's no reason I need to work with eV.

 

[Reality Check]

You have the energy that is stored in the magnetic field, and the energy available from the flux tubes connected to the solar surface.
This energy is available up to the point of the "null" or particle jets, and then only the energy of the flux tubes is available until the magnetic field builds up again.

This is all from the kinetic energy of the particles.

Wrong.
The energy from the magnetic fields is always available to the magnetic reconnection at the "null" point.
You have forgotten the basics yet again: The flux tubes are created 1000's of kilometers away from the solar surface by currents that no longer exist.
And lets repeat the points you are not understanding:

• The only kinetic energy that is available to the solar flare is from particles that can get to the release point in 100 seconds.
• All of the energy in the magnetic field is available to be released in the flare (subject to light speed of course). The magnetic field of a solar flare has a large volume (1000's of cubic kilometers? at a guess) and a non-zero energy density.

So be surprised - the physics states you are wrong !

The moving particles create the magnetic field. When the flow stops(or changes direction) the magnetic field collapses and releases energy.
Reconnection.

It is impossible for the moving charges of the coronal loop in solar coronal loops to create the magnetic field. This has been pointed out to you many times and yet you cannot understand this simple point.

There is nothing inconsistent to what I'm saying.
I am following the right hand rule which indicates the magnetic field is produced by moving particles except in the filed aligned case, although there is still a small parallel component in non field aligned currents..

So is everyone else.
The right hand rule means that the current in the flux tube cannot be creating the flux tube. This is plasma - the right hand rule means that the current is destroyed as it is smeared out into current sheets.
(e.g. see Magnetic reconnection via current sheets, D. Biskamp, Phys. Fluids 29, 1520 (1986); doi:10.1063/1.865670)

The only thing you might be able to say is that a direct measurement of the particle count and temperature of a flux tube doesnt match the magnetic field.
If so I would like to see that paper.

That question is strange.

Of course the counts of particles in a flux tube "match" the magnetic field - they are inside it!

And I have no idea what the "temperature of a flux tube" means or has to do with the magnetic field. Maybe you mean the temperature of the plasma in a flux tube but that has nothing to do with sustaining the magnetic field of the flux tube. Maybe you are just derailing into the coronal heating problem.

P.S.
First asked 21 February 2010
brantc,
What are your citations for your assertion that kinetic energy is the primary source for energy in magnetic reconnection?

1. This should answer the previous 2 questions
   What is the energy released from the kinetic energy of the currents?
2. How does this energy compare to the energy released in magnetic reconnection?

from some of the 100's of papers on the subject, many of which you have read to form your conclusion.

 

[Tubbythin]

I agree with you that it is not unique. In this instance I use eV when talking about particles and particle energy (besides Joules) because it is a more fundamental quality.

No it isn't!

 

[brantc]

I could do that any number of ways. Temperature is just as good a metric as energy, and unlike velocity and energy there IS a unique conversion from one to the other (and not just for plasmas) in the form of Boltzmann's constant k. And if I did it in units of energy, I could use Joules instead, there's no reason I need to work with eV.

So when you talk about an electron, you talk about its energy in Joules?

 

[sol invictus]

So when you talk about an electron, you talk about its energy in Joules?

Particle physicists tend to use eV (or keV, MeV, meV, etc.). But that's nothing more or less than a linguistic convention among a specific subgroup of humanity.

Measuring an electron's energy in Joules is no more strange or surprising than measuring the speed of a sailboat in m/s rather than knots, the mass of a piece of cheese in ounces, or the area of an apartment in hectares.

The fact that you believe otherwise is decidedly odd.

 

[Tim Thompson]

Particles & Fluids & MHD II

I never said MHD does not apply to astrophysical plasma.

Hey, I am just following your lead. You're the one who made a point out of citing a wiki page which implied exactly that. So if that implication is not what you intended, why did you post the quote in the first place?

My contention from the beginning is that MHD does not tell you the whole story.

Well, since MHD is an approximation, I think that's a given, is it not?

PIC simulation will tell the whole story because it explicitly treats particles kinetically.

Well, maybe, but there is an issue of practicality involved. After all ...

"To completely describe a plasma at any time requires knowing the position and velocity of each particle of each type, for example, the position and velocity of each electron and ion. Each particle position and velocity changes under the influence of the electromagnetic fields, and we must know these fields at every point. Further, these fields change according to Maxwell's equations in which the current is obtained from the particle positions and velocities."

"As a practical matter, we must give up such infinite precision and deal with the statistical distribution of the particle positions and velocities. Then from these distributions we can obtain a reasonable value of the charge and current densities that produce the E and B fields that move the particles. Similarly, the statistical distribution of the particle densities and currents is influenced by the electric and magnetic fields."

Plasma Physics fro Astrophysics by Russell Kulsrud, Princeton University Press 2005; section 1.1 "How Do We Describe a Plasma and Its Electromagnetic Fields", page 6.
​

Obviously, the number of particles can quickly grow beyond our computational ability, so the fluid approximation of MHD is a necessity. However, approximation though it may be, do keep in mind my earlier quote, this time with emphasis added by me...

Paragraph 2
"Because MHD does not explicitly treat individual particle motions, it may at first be thought that it is of little use in collisionless plasmas. However, MHD is always a correct description of the large-scale bulk dynamics of a fluid, with or without internal collisions, so long as the fluid cannot support a significant electric field in its own reference frame."
Magnetic reconnection, Priest & Forbes, section 1.7 "Relevance of MHD to Collisionless Systems", page 38.

I note the use of the word "always". So long as the stated criteria are met, MHD is always correct. There will be no circumstance under which one will find a PIC, or other kinetic-particle description of the plasma, to be correct while MHD is found to be wrong. And keep in mind the admonition of Tusenfem, who said ...

I do hope you realize that MHD does not have any particles, it is a fluid description of the plasma, which fails when you want to look at spatial scales smaller than the ion gyro radius or at temporal scales shorter than the ion gyration time.

So add the natural criterion stated here that MHD will become invalid once we are dealing with spatial scales that are too small for the fluid approximation to correctly describe collective particle behavior.

The streaming electrons in the LAPD experiment caused the flux tubes to form in that experiment.
It was the imbalance of electrons(electric field potential) near the electrodes that caused the streaming motion towards the opposite end of the experiment..
This caused a "flux tube to form with 2 filaments with opposing fields that touched in many places with many sites for reconnection".
With radiation and jets etc.....
Model that with MHD.

I don't have to, it has already been done. I refer back to your original source ...

http://plasma.physics.ucla.edu/paper...n_IEEE2008.pdf

Read the very last sentences of the paper: "We stress that this is a reconnection mediated by the current systems of Alfven waves. It is the motion of these currents/waves that force magnetic field lines together and trigger local reconnection." The authors stress the role of Alfven waves. But Alfven waves are normal mode MHD waves (e.g., Fundamentals of Plasma Physics, Paul Bellan, Cambridge University Press 2006, page 155). The paper you cite explicitly credits MHD. Is it your contention that the authors are wrong? Is it perhaps your contention that there were actually no Alfven waves present?

OK, you posted a webpage quote, only to say you don't believe the quote you posted. And now you post claims about a plasma experiment which are contradicted by the paper you posted. This is not a spiffy track record.

Your suppose to be a scientist? and you make comments like this.....

"The fact that MHD does not explicitly treat particles in a plasma is of no more consequence than the fact that hydrodynamics does not explicitly treat molecules of water but is still able to represent the physics of water waves with remarkable clarity & correctness."

I do indeed and I stand by every word. It is a correct statement. I submit that you have yet to disclose any flaw in the logic or the physics involved in it.

I never said MHD was wrong, its just being misapplied.

Do you have another example, since the last one has been negated? Where and under what conditions is MHD misapplied and by whom? And how do you know it is a misapplication?

 

[brantc]

Particle physicists tend to use eV (or keV, MeV, meV, etc.). But that's nothing more or less than a linguistic convention among a specific subgroup of humanity.

Measuring an electron's energy in Joules is no more strange or surprising than measuring the speed of a sailboat in m/s rather than knots, the mass of a piece of cheese in ounces, or the area of an apartment in hectares.

The fact that you believe otherwise is decidedly odd.

Ok. What should I do to make you happy since you seem to nitpicking my usage of eV to death??? I mean we are talking physics............

I never said it was odd. Its just that the Ev is the most convenient unit (ok, for me)when talking particles that move.

 

[brantc]

Originally Posted by brantc View Post
Your suppose to be a scientist? and you make comments like this.....

"The fact that MHD does not explicitly treat particles in a plasma is of no more consequence than the fact that hydrodynamics does not explicitly treat molecules of water but is still able to represent the physics of water waves with remarkable clarity & correctness."

I do indeed and I stand by every word. It is a correct statement. I submit that you have yet to disclose any flaw in the logic or the physics involved in it.

Remarkable clarity and correctness.
That maybe so but it does not give you the details of particle movement.

Good approximation. Do you know what that means?
That means it works for some stuff but not other stuff.

That means if you want to know the whole story, this tool will not give it to you. Same with MHD. It is only good to a certain level of detail.

I know you cant tell me that MHD has modeled reconnection perfectly.

Who give a twaddle about computing power!!!!!
Someday you will be able to run a complete PIC simulation with the physical layout of the flux tubes.

That has nothing to do with whether PIC is more accurate than MHD.