Talk:Magnetic reconnection

Creation of Archive

Because the previous talk page had become host to protracted discussions during and prior to an edit war and had not been edited in about nine months, it has been archived. My hope is that this will help the discussion to focus again on how to improve this article. Spacehippy (talk) 00:16, 11 September 2012 (UTC)

Brainstorming ideas on how to improve this article

Here are some thoughts I've had on how to improve this article.

• Condense article header into ~1 paragraph
• Shorten the discussion Sweet-Parker reconnection (probably no need to include the entire derivation)
• Add a section or discussion on the differences between 2D and 3D reconnection, and the types of reconnection in 3D
• Expand discussion on collisionless reconnection and perhaps include a figure showing the quadrupole fields associated with Hall reconnection
• Improve the discussion for observational evidence and consequences for the solar atmosphere
• More fully explain where and how reconnection occurs in planetary magnetospheres
• Expand the discussion on where reconnection occurs in laboratory experiments
• Include a discussion on where reconnection is thought to occur in other astrophysical situations (interstellar medium, magnetized turbulence, the solar wind, pulsar magnetospheres, etc.)
• Figures showing reconnection in solar flares, the Earth's magnetosphere, and laboratory plasmas.

Spacehippy (talk) 00:37, 11 September 2012 (UTC)

I agree with the archival, and would like to help with this, but my first contribution has been to lengthen the header. Sorry about that, but I think it important to cross link with the solar physics reconnection community. I pointed out the 2D/3D distinction though more could well be said, especially now that there are detailed 3D particle in cell simulations. The MMS mission reference is good, but more could be added that has been published from that mission. Diagrams would be useful to add, including from laboratory studies. Magnetic fields are increasingly studied in astrophysics, so I hope that will be brought in as well. What do we think about including a section on the criticisms of reconnection theory? I believe all the criticisms have been answered and the reality of the process has been amply demonstrated both by improving observations and theoretical simulations. I'd be willing to write such a section from a neutral point of view. Thosem (talk) 20:14, 25 July 2023 (UTC)

I have drafted a section on criticisms of magnetic reconnection in my sandbox. Please have a look and comment.

User:Thosem/sandbox#Criticism_of_magnetic_reconnection Thosem (talk) 19:15, 26 July 2023 (UTC)

The other proposed theory

Hi, at the moment the last paragraph in the introduction finishes with: There are two competing theories to explain the discrepancy. One posits that the electromagnetic turbulence in the boundary layer is sufficiently strong to scatter electrons, raising the plasma's local resistivity. This would allow the magnetic flux to diffuse faster.

I was just wondering, what would the other competing theory be? Thanks — Preceding unsigned comment added by 193.49.162.11 (talk) 21:27, 3 March 2013 (UTC)

Is there a reason this is in MKSA instead of CGS?

Pretty much anyone who is studying this topic will be doing so in cgs units. I am wondering if it wiki policy work in SI for all science pages or if there is some other reason for the SI units on this page. Gunblader928 (talk) 05:07, 13 November 2013 (UTC)

SI is the international norm, and is most widely used in science. bobrayner (talk) 23:52, 13 November 2013 (UTC)

everyone in this community uses CGS, experimentalists, theoreticians and numerical people alike. If there is no strict policy it would benefit readers to have everything in CGS. Justinh2002 (talk) 06:17, 22 December 2022 (UTC)

The statement that everyone uses CGS is false, if only because it makes it sound like there is only one CGS system. This is not true: in there is an electrostatic CGS system, an electromagnetic CGS system, the Gaussian CGS system, and a CGS Lorentz-Heaviside system, and others. Of these the Gaussian is the most frequently used but most users are not aware of the distinctions. This has the potential to cause error and confusion with different unit names, sizes, and definitions in terms of the base units and different coefficients for the major equations of electromagnetism. This is one of the great advantages of SI units (the successor to MKS and very similar to MKS) which is coherent and standardised. If one uses dimensional analysis to any great extent, one quickly realises the great advantages of SI over CGS which it replaced for very good reasons. It is true that the various forms of CGS are still used in certain disciplines but they really should not be: I always teach undergraduate students to ensure that they put everything in SI units as that ensures that their answer is in the relevant SI units and avoids several pitfalls, especially in electromagnetism. MessageInABottle 08:00, 22 December 2022 (UTC) — Preceding unsigned comment added by MichaelLockwood (talk • contribs)

Heading rewording

I feel a bit uneasy with the current wording "magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration". The problem I have is that kinetic energy is closely related to thermal energy and with particle acceleration. Also, the same could be said about particle acceleration and thermal energy. So maybe a rewording is necessary, either by retaining kinetic energy and moving to a parenthesis the thermal energy and particle acceleration as possible forms of kinetic energy, either to emphasize the differences between them - i.e. thermal energy could refer to a (dense) plasma while particle acceleration could be related to very thin plasmas or cosmic particles.217.91.240.26 (talk) 10:11, 17 November 2013 (UTC)

Actually, the primary process during magnetic reconnection is charged particle acceleration. These accelerated particles may then heat the plasma. Ruslik_Zero 13:07, 17 November 2013 (UTC)

That could be a great addition to the article if you have references. And that will partly solve the redundancy problem. An by the way - charge particle acceleration = transfer of kinetic energy.217.91.240.26 (talk) 19:56, 20 November 2013 (UTC)Apass

"Kinetic energy" maybe also have been intended to refer to the bulk flows which result from reconnection. Even if not, bulk flows may be worth mentioning. 129.2.106.74 (talk) 21:39, 22 November 2013 (UTC)

A good review is here.

Magnetic reconnection involves a topology change of a set of field lines, which leads to a new equilibrium configuration of lower magnetic energy. During this process magnetic energy is converted to kinetic energy through acceleration or heating of charged particles.

or

When the field lines are reconnected, the topology of magnetic configuration changes and j×B forces result in the conversion of magnetic energy to kinetic energy

or

The true energy conversion mechanism is Ohmic dissipation acting differentially to change the shape of the magnetic lines so that they develop a strong curvature in the current layer. This change itself releases only a small amount of energy. The main conversion is caused by the curved lines unfolding and accelerating the plasma out of the ends of the current layer, simultaneously lowering the magnetic energy, accelerating the plasma, and increasing its kinetic energy. This kinetic energy leads to shocks and viscous dissipation which turns the energy into radiation and accelerates particles. This sequence of events is termed magnetic reconnection although it is only the first stage that involves physical reconnection of the magnetic lines.

It seems to depend on the direction of E filed: where it is parallel to B field it accelerates particles (short circuit); where it is orthogonal to B field it causes bulk motion of plasma. Both processes can heat the plasma eventually. Ruslik_Zero 12:14, 25 November 2013 (UTC)

On kinetic and thermal energy. it is absolutely true, of course, that thermal energy is kinetic - but it is the kinetic energy of random thermal motions not of bulk flow and so there is a distinction here. Reconnection generates accelerated bulk flows in the outflow region as well as heating, so it raises both, But one can have one without the other. I suggest adding the words "bulk-flow" so we talk about "bulk-flow kinetic energy" as that is a distinct thing from thermal kinetic energy. MessageInABottle 10:41, 22 December 2022 (UTC)

This is not true in areas like solar physics and space physics where the topology change of the magnetic field is in many ways more important than the the particle energisation. The point being that that without reconnection, magnetic fields would become ever more entangled and twisted and reconnection is the mechanism that returns the system to a lower-energy configuration. MessageInABottle 08:04, 22 December 2022 (UTC) — Preceding unsigned comment added by MichaelLockwood (talk • contribs)

Regarding the direction of E-field: magnetic reconnection is a non-ideal process (regardless of the phenomenology of the energy conversion) and thus depends only on the properties of the parallel electric field, E + v x B = R, where R is a general non-ideal term (see Schindler et al.. 1988, J. Geophys. Rev., 93, A6, 5547, and Hesse & Schindler, 1988, J. Geophys. Rev., 93, A6, 5559). Perpendicular E-fields are fully described by ideal processes, E + v x B = 0, which preserves the connectivity topology of lines of force (see e.g., Moffatt, H. K., 1985, J. Fluid Mech., 159, 359).

Research Article: Electron-scale measurements of magnetic reconnection in space

A paper was published today in the journal Science which describes observations made by NASA’s Magnetospheric Multiscale Mission (MMS). That mission made direct measurements of electron demagnetization and acceleration during reconnections along the sunward boundary of Earth’s magnetosphere where the magnetic field between the Sun and Earth reconnects with the terrestrial magnetic field. The measurements were made with very high temporal resolution. Here is a link to the article: [1] Sparkie82 (t•c) 11:17, 13 May 2016 (UTC)

Difficult to understand

Hey folks,

I am a first-year Physics Ph.D. student, and I am about halfway through a basic plasma class. I feel like I am the target audience for this article. Nonetheless, this article is impossible to understand. I have a basic understanding of mechanics, electrodynamics, and magnetohydrodynamics. Nonetheless, this article is at too high of a level to understand very well.

128.235.93.40 (talk) 18:13, 22 October 2020 (UTC)

Please update with: "Magnetic reconnection as a mechanism for energy extraction from rotating black holes"

I think some information on this study should be added to the article. It's currently featured in 2021 in science like so:

Astrophysicists report that energy extraction – with high efficiency – from rotating black holes with a high spin via reconnection of magnetic field lines of an externally supplied magnetic field that accelerates escaping plasma particles is possible. Advanced civilizations may be capable of doing so.

and:

Astrophysicists report a new way for energy extraction from rotating black holes that have a high spin. Reconnection of magnetic field lines of an externally supplied magnetic field would accelerate plasma particles escaping the black hole. Advanced civilizations may be capable of harnessing energy this way with high efficiency. This may be relevant to the search for extraterrestrial intelligence and the accuracy of the Kardashev scale.

I don't think it would fit into any of the article's existing sections so a new section should probably be added.

--Prototyperspective (talk) 18:29, 27 February 2021 (UTC)

References

Flawed

Magnetic reconnection (MC) is a convenient fiction. Perhaps the editors are too close to the physics to realize that the average reader doesn't know that simple fact. It should be explained that field lines are abstractions just like contour lines on a topological map (of land) are. "Explaining" MC as the breakdown of "ideal-magnetohydrodynamics" is as helpful as explaining a phonon as a type of quasiparticle. It explains nothing (unless the reader is already well versed in the subject). The article seems to have been written to be INTENTIONALLY vague. I learn that MC can be slow (how slow? no idea, millions of years? dozens of nanoseconds, no idea) or fast (how fast? again, no idea). I also read that regions of large magnetic shear are small...(how small? no idea - we're talking about the Sun and the solar system so could be femtometers or megameters, make sure to not explain what's meant!). It would be nice to reduce the process to the motion of real stuff. Like plasma is real, electrons are real, and so are their electrical and magnetic fields (for certain values of real), but field lines? not so much. (As far as I know, iron dust aside, you can't measure field lines like you can measure field strength, right?). Anyway, let me finish by stating that Alfven himself advised against use of the concept. To be clear, I'm not arguing that it shouldn't be invoked, but am arguing that it has some very significant problems and it's easy to find criticism of it online, and they should be discussed!174.130.71.156 (talk) 08:54, 17 January 2023 (UTC)

Consistency of attribution

This article is inconsistent with the article on Ron Giovanelli, who is credited widely with the first conception of magnetic reconnection as an energy source for solar flares. The two articles should be made consistent by crediting Giovanelli here and linking to the article on him. Thosem (talk) 15:01, 14 March 2023 (UTC)

Since I'm new at this and have a COI, here's what I propose to replace the introductory section of this article, for review and comments.

Magnetic reconnection is a physical process occurring in electrically conducting plasmas, in which the magnetic topology is rearranged and magnetic energy is converted to kinetic energy, thermal energy, and particle acceleration.^[1] Magnetic reconnection involves plasma flows at a substantial fraction of the Alfvén wave speed, which is the fundamental speed for mechanical information flow in a magnetized plasma.

The concept of magnetic reconnection was developed in parallel by researchers working in solar physics and in the interaction between the solar wind and magnetized planets. This reflects the bidirectional nature of reconnection, which can either disconnect formerly connected magnetic fields or connect formerly disconnected magnetic fields, depending on the circumstances.

Ron Giovanelli is credited with the first publication invoking magnetic energy release as a potential mechanism for particle acceleration in solar flares.^[2] Giovanelli proposed in 1946 that solar flares stem from the energy obtained by charged particles influenced by induced electric fields within close proximity of sunspots.^[3] In the years 1947-1948, he published more papers further developing the reconnection model of solar flares.^[4] In these works, he proposed that the mechanism occurs at points of neutrality (weak or null magnetic field) within structured magnetic fields.

James Dungey is credited with first use of the term “magnetic reconnection” in his 1950 PhD thesis, to explain the coupling of mass, energy and momentum from the solar wind into Earth's magnetosphere.^[4] The concept was published for the first time in a seminal paper in 1961.^[5] Dungey coined the term "reconnection" because he envisaged field lines moving together in an inflow toward a magnetic neutral point (2D) or line (3D), breaking apart and then rejoining again but with different magnetic field lines, in an outflow away from the magnetic neutral point or line.

In the meantime, The first theoretical framework of magnetic reconnection was established by Peter Sweet and Eugene Parker at a conference in 1956. Sweet pointed out that by pushing two plasmas with oppositely directed magnetic fields together, resistive diffusion is able to occur on a length scale much shorter than a typical equilibrium length scale.^[13] Parker was in attendance at this conference and developed scaling relations for this model during his return travel.^[14]

1. Mozer, F.S., & Pritchett, P.L. (June 2010). "Magnetic field reconnection: A first-principles perspective". Physics Today. 63 (6): 34–39. Bibcode:2010PhT....63f..34M. doi:10.1063/1.3455250.
2. Birn, Joachim (3 June 2011). "Magnetic Reconnection in Plasmas". Eos: Earth & Space Science News. 83 (22): 250. doi:10.1029/2002EO000175.
3. Giovanelli, R.G. (20 July 1946). "A Theory of Chromospheric Flares". Nature. 158 (4003): 81–82. Bibcode:1946Natur.158...81G. doi:10.1038/158081a0. S2CID 4139384.
4. Giovanelli, R.G. (1947). "Magnetic and Electric Phenomena in the Sun's Atmosphere associated with Sunspots". Monthly Notices of the Royal Astronomical Society. 107 (4): 338–355. Bibcode:1947MNRAS.107..338G. doi:10.1093/mnras/107.4.338.

Thosem (talk) 17:37, 25 July 2023 (UTC)

Proposed New Section

For comment:

History of Criticism

The reconnection concept has been criticized bitterly ever since it was proposed. It suffered the biggest blow when dismissed by the respected Nobel Prize winning scientist, Hannes Alfvén, who is widely considered to be the “Father of Magnetohydrodynamics”, discoverer of the "Alfvén wave", and the author of “Alfvén’s Theorem”. This theorem, often referred to as the “frozen-in” flux theorem, states that two plasma parcels that are initially connected by a magnetic field line will continue to be connected by a common magnetic field line as they move around. A relatively recent summary of the critiques was given by Falthammar [2007], who wrote:

“The magnetic field B is a vector field defined as a function of space coordinates and time. At a fixed time, one may trace a field line away from any given point in space. But that field line has no identity, and in a time-dependent magnetic field it cannot be identified with any field line at a different time, except by one convention or another.”

Alfvén’s theorem does not state that the field line has an identity and moves with the plasma parcels, though many have found it useful to think of it that way. The theorem states only that connected fluid parcels continue to be connected by a common field line as they move. It is perhaps misleading but also unnecessary to regard the field line as having an identity associated with the fluid and moving with it.

The situation is resolved by the fact that magnetic "lines of force" exert forces on a conducting fluid, which can be decomposed into a magnetic pressure force transverse to the field lines and a magnetic tension force along the field lines. Together, these are identified in MHD theory as a force proportional to the vector product of local current density and the magnetic field intensity (JxB). Thus, magnetic field lines act in a way analogous to a web of fibers permeating the conducting fluid or plasma, like those of striated muscle tissue or fiberglass. These electromagnetic forces make it both tempting and useful to think of the field lines as moving with the fluid as they exert forces on it. The tension force in particular gives rise to an intuitive analogy with elastic bands, with the magnetic lines of force acting somewhat like a slingshot that propels fluid parcels.

Reconnection involves violations of Alfvén's theorem, such that fluid parcels may become separated from other parcels to which they were once connected, and "reconnected" to other fluid parcels to which they were not formerly connected. In that process, magnetic flux is transported along with the fluid flow, so the overall magnetic topology is altered, and in general becomes time dependent. It should not be too much of a surprise that Hannes Alfvén resisted the idea whose main usefulness lies in describing how his theorem is violated at times and in places.

So "magnetic reconnection" could seemingly have been called “plasma reconnection” since it is a change in magnetic topology that violates Alfvén’s theorem and reconnects plasma parcels that once were connected so that they are no longer connected, or vice versa. Since the connecting agent is the magnetic field, “magnetic reconnection” is not inappropriate, either.

References

— Preceding unsigned comment added by Thosem (talk • contribs) 20:44, 26 July 2023 (UTC)

Hey. Thanks for taking the time to write this up. In my opinion, with a few modifications this would fit well in a new "History" section. Some comments:

• The section deviates from WP:summary style at a few points (e.g., with the use of "indeed", "and yet"; see WP:EDITORIAL) so these should be rephrased or removed.
• I think we should also focus more on criticism of reconnection rather than on criticism of moving magnetic field lines. (Perhaps some of this info on moving magnetic field lines would fit better in the Alfvén's theorem article.)
• Fälthammar 2007 does not seem to support that Alfvén opposed reconnection (I am also skeptical), so this info will need its own citation or will have to be removed.
• The last paragraph seems to be just opinion, so I do not think it is necessary here.

Thanks again for adding this. I hope to address the other talk section you added sometime soon. CoronalMassAffection (talk)

Thanks for the comments. Maybe it could be "History of Criticisms".

I see your point about "indeed" and "yet" and would edit them out.

Alfvén was by far the most prominent critic, given his Nobel Prize and pioneering work. Other critiques of reconnection tend to be in the form of "it's a bunch of nonsense, as even Alfvén noted." I've found no credible argument that it would require magnetic monopoles, and it has proven extremely durable, with multiple space missions having refined observations of it over decades, about which I also plan to develop more material for this article.

There is a paragraph toward the end of Falthammar 2007 quoting Alfvén as warning against the use of "frozen-in" and moving field lines (useful in cases but often misleading). Also a 1976 Alfvén paper is cited in which he criticizes the concept of "field line reconnection". So Falthammar definitely does note that Alfvén came to oppose reconnection in his later years, as is widely claimed (for example in the archived Talk page material, among which is an objection to the lack of a section on criticisms of the concept).

The last paragraph could be written so that it's more of an observation about terminology than an opinion.

Thosem (talk) 21:32, 27 July 2023 (UTC)