This is the
talk page for discussing improvements to the
Magnetic reconnection article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Archives: 1 |
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||||||||||||
|
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host to protracted discussions during and prior to an edit war and had not been edited in about nine months, it has been archived.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)
Here are some thoughts I've had on how to improve this article.
Spacehippy ( talk) 00:37, 11 September 2012 (UTC)
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)
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)
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)
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.
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
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.
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).
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)
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)
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. [1] [2]
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
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)
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)
![]() | The following Wikipedia contributor has declared a personal or professional connection to the subject of this article. Relevant policies and guidelines may include conflict of interest, autobiography, and neutral point of view. |
For comment:
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] [1], 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). [2] 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)
This is the
talk page for discussing improvements to the
Magnetic reconnection article. This is not a forum for general discussion of the article's subject. |
Article policies
|
Find sources: Google ( books · news · scholar · free images · WP refs) · FENS · JSTOR · TWL |
Archives: 1 |
![]() | This article is rated Start-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | ||||||||||||||||||||
|
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)
Here are some thoughts I've had on how to improve this article.
Spacehippy ( talk) 00:37, 11 September 2012 (UTC)
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)
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)
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)
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.
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
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.
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).
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)
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)
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. [1] [2]
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
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)
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)
![]() | The following Wikipedia contributor has declared a personal or professional connection to the subject of this article. Relevant policies and guidelines may include conflict of interest, autobiography, and neutral point of view. |
For comment:
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] [1], 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). [2] 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)