Magnetic Reconnection vs Double Layers


    Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another, changing their patterns of connectivity with respect to the sources. It is a violation of an approximate conservation law in plasma physics, and can concentrate mechanical or magnetic energy in both space and time. Solar flares, the largest explosions in the solar system, may involve the reconnection of large systems of magnetic flux on the Sun, releasing, in minutes, energy that has been stored in the magnetic field over a period of hours to days. Magnetic reconnection in Earth's magnetosphere is one of the mechanisms responsible for the aurora, and it is important to the science of controlled nuclear fusion because it is one mechanism preventing magnetic confinement of the fusion fuel.

    Magnetic reconnection is something that has supposedly been "tested" and proven in the lab yet for some reason the lab results keep coming out "wrong."

    Currently when scientists create a "reconnection" event in the lab between two electrically charged plasma sheets the "reconnection" event takes place at twice the speed MHD theory predicts.

    So far no one has been able to rectify this problem, nor have they been able to produce a "reconnecting" magnetic field without first applying current to the plasma sheets they are observing. The reason being obvious of course, in order to create a magnetic field, one must first induce an electrical current. So far, this is the only known way of producing a magnetic field in a plasma that can be tested.

    As soon as the current shuts off, so too does the magnetic field.

    Magnetic reconnection is proposed to account for the sudden bursts of observed kinetic energies that power the aurora's substorms and light up the polar skies. It’s also proposed to account for about a billion other phenomena that I will not get into here.

    Focusing on the aurora, some very interesting facts come to light.

    THEMIS, Viking, FAST, UARS and several other satellites have confirmed the existence of parallel electric fields powering the auroras. Electric fields of course must complete a circuit in order to flow. Without charge deficiency in one area of space, there would be no current flow which is a product of charge equalization.

    Some papers on the findings of parallel electric field aligned currents, otherwise known as "Birkeland currents" after Kristian Birkeland, the man who postulated their existence back in 1901.
    Quasi-static, magnetic-field-aligned (parallel) potentials have been considered the primary source of charged particle acceleration in the aurora where precipitating electrons create a visible display. This finding has been controversial since, at one time, it was widely believed that parallel potentials could not be supported by a collisionless plasma. We present observations from the fast auroral snapshot (FAST) satellite which strongly support this acceleration mechanism and, moreover, show evidence of a second plasma regime region which supports quasi-static parallel potentials.
    Electron distribution functions measured on the Dynamics Explorer 1 spacecraft are shown to have the characteristics expected in a region of parallel electric fields.
    Using plasma wave data sampled by the Freja spacecraft from the topside ionosphere during auroral conditions, the possible existence of electric fields with an intense parallel component (a few tens of millivolts per meter) with respect to the Earth's magnetic field is discussed.
    We present a survey of 64 direct observations of large-amplitude parallel electric fields E∥ in the upward current region of the southern auroral acceleration zone, obtained by the three-axis electric field experiment on Polar.
    Satellite observations have established that parallel electric fields of both upward and downward current regions of the aurora are supported, at least in part, by strong double layers.
    It is demonstrated that the simultaneous observations on Viking of upward field-aligned fluxes of energetic ions and electrons of energies in the same range may be due to acceleration in field-aligned electric fields, the ions in an upward directed parallel dc field and the electrons in a downward directed parallel field which is fluctuating but appears as quasi-static for the electrons as long as they are in the acceleration region.
    Magnetic field and particle observations from the Upper Atmosphere Research Satellite particle environment monitor (UARS/PEM) are used to estimate field-aligned currents, electron precipitation energy flux, ionospheric conductivities, and Joule heating rates during the main phase of the November 4, 1993, geomagnetic storm.

    Given that we know field aligned electrical currents exist in the space plasma surrounding earth, some fundamental properties of conducting plasma can be employed to describe the events many astrophysicists currently ascribe to “magnetic reconnection.”

    So let’s look at some papers, the models, and how they are related to the observed phenomena.

    R. E. Ergun et al.: Double layers in the downward current region of the aurora
    Nonlinear Processes in Geophysics (2003) 10: 45–52
    These results suggest that large double layers can
    account for the parallel electric field in the downward current
    region and that intense electrostatic turbulence rapidly stabilizes
    the accelerated electron distributions. These results also
    demonstrate that parallel electric fields are directly associated
    with the generation of large-amplitude electron phasespace
    holes and plasma waves….

    We presented direct observations of the parallel electric field
    in the downward current region of the auroral zone. The observations
    are consistent with a strong double layer moving
    along B at the ion acoustic speed in the same direction of the
    accelerated electrons. The potential drop extends _10 _D
    along B. Intense electrostatic emissions are spatially separated
    from the structure on the high-potential side. Electron
    phase-space holes emerge from the wave turbulence associated
    with the double layer.

    The potential structure accelerates electrons to several
    times their initial thermal velocity which results in a factor
    of 10 gain from the initial thermal energy. Intense quasielectrostatic
    wave emissions and electron phase-space holes
    rapidly modify the accelerated electron distribution. Part of
    the electron distribution (stagnating electrons) is reflected
    back into the double layer through interaction with the intense
    wave turbulence. Thus, the intense wave turbulence
    may interact with the double layer through this stagnating
    electron population.

    Singh, N., and G. Khazanov (2003), Double layers in expanding plasmas and their relevance to the auroral plasma processes, J. Geophys. Res., 108(A4), 8007, doi:10.1029/2002JA009436.
    When a dense plasma consisting of a cold and a sufficiently warm electron population expands, a rarefaction shock forms [ Bezzerides et al., 1978 ]. In the expansion of the polar wind in the magnetosphere, it has been previously shown that when a sufficiently warm electron population also exists, in addition to the usual cold ionospheric one, a discontinuity forms in the electrostatic potential distribution along the magnetic field lines [ Barakat and Schunk, 1984 ]. Despite the lack of spatial resolution and the assumption of quasi-neutrality in the polar wind models, such discontinuities have been called double layers (DLs). Recently similar discontinuities have been invoked to partly explain the auroral acceleration of electrons and ions in the upward current region [ Ergun et al., 2000 ]. By means of one-dimensional Vlasov simulations of expanding plasmas, for the first time we make here the connection between (1) the rarefaction shocks, (2) the discontinuities in the potential distributions, and (3) DLs. We show that when plasmas expand from opposite directions into a deep density cavity with a potential drop across it and when the plasma on the high-potential side contains hot and cold electron populations, the temporal evolution of the potential and the plasma distribution generates evolving multiple double layers with an extended density cavity between them. One of the DLs is the rarefaction-shock (RFS) and it forms by the reflections of the cold electrons coming from the high-potential side; it supports a part of the potential drop approximately determined by the hot electron temperature. The other DLs evolve from charge separations arising either from reflection of ions coming from the low-potential side or stemming from plasma instabilities; they support the rest of the potential drop. The instabilities forming these additional double layers involve electron-ion (e-i) Buneman or ion-ion (i-i) two-stream interactions. The electron-electron two-stream interactions on the high-potential side of the RFS generate electron-acoustic waves, which evolve into electron phase-space holes. The ion population originating from the low-potential side and trapped by the RFS is energized by the e-i and i-i instabilities and it eventually precipitates into the high-potential plasma along with an electron beam. Applications of these findings to the auroral plasma physics are discussed.

    Quoting dic.academic’s definition of a double layer

    Current carrying double layers may arise in plasmas carrying a current. Various instabilities can be responsible for the formation of these layers. One example is the Buneman instability which occurs when the streaming velocity of the electrons (basically the current density divided by the electron density) exceeds the electron thermal velocity of the plasma. Double layers (and other phase space structures) are often formed in the non-linear phase of the instability. One way of viewing the Buneman instability is to describe what happens when the current (in the form of a zero temperature electron beam) has to pass through a region of decreased ion density. In order to prevent charge from accumulating, the current in the system must be the same everywhere (in this 1D model). The electron density also has to be close to the ion density (quasineutrality), so there is also a dip in electron density. The electrons must therefore be accelerated into the density cavity, to maintain the same current density with a lower density of charge carriers. This implies that the density cavity is at a high electrical potential. As a consequence, the ions are accelerated out of the cavity, amplifying the density perturbation. Then there is the situation of a double-double layer, of which one side will most likely be convected away by the plasma, leaving a regular double layer. This is the process in which double layers are produced along planetary magnetic field lines in so-called Birkeland currents.

    Another known property of charged plasma that can explain the sudden and dramatic bursts of kinetic energy we see in the aurora substorms is something called an “exploding double layer.”

    Given that we have parallel currents and double layers in the surrounding regions of earths magnetosphere; a simple explanation arises for the sudden substorms:

    Stability: Double layers in laboratory plasmas may be stable or unstable depending on the parameter regime. [Torven, S. High-voltage double layers in a magnetised plasma column] " (1982) "Journal of Physics D: Applied Physics", Volume 15, Issue 10, pp. 1943-1949] Various types of instabilities may occur, often arising due to the formation of beams of ions and electrons. Unstable double layers are "noisy" in the sense that they produce oscillations across a wide frequency band. A lack of plasma stability may also lead to a dramatic change in configuration often referred to as an explosion (and hence "exploding double layer"). In one example, the region enclosed in the double layer rapidly expands and evolves. [B Song, N D Angelo and R L Merlino Stability of a spherical double layer produced through ionization] " (1992) Journal of "Physics D: Applied Physics", Volume 25, Issue 6, pp. 938-941] An explosion of this type was first discovered in mercury arc rectifiers used in high-power direct-current transmission lines, where the voltage drop across the device was seen to increase by several orders of magnitude. Double layers may also drift, usually in the direction of the emitted electron beam, and in this respect are natural analogues to the smooth--bore magnetron. [ Koenraad Mouthaan and Charles Süsskind, Statistical Theory of Electron Transport in the Smooth-Bore Magnetron] (1966) "Journal of Applied Physics" June 1966, Volume 37, Issue 7, pp. 2598-2606 ] ) (not to be confused with a unit of magnetic moment, the Bohr magneton, which is created by the "classical circular motion" of an electron around a proton).

    This idea was put forth by Hannes Alfven after the rectifier incident noted above.

    Double layers and circuits in astrophysics
    Alfven, Hannes IEEE Transactions on Plasma Science (ISSN 0093-3813), vol. PS-14, Dec. 1986, p. 779-793

    Continuing on with “magnetic reconnection” as a theory, we find it violates known laws of physics. Fälthammar, does an excellent job describing the problems with “magnetic reconnection” theory as it pertains to real current carrying plasmas here:

    On the Concept of Moving Magnetic Field Lines
    Eos, Vol. 88, No. 15, 10 April 2007
    Alfvén, who had introduced the concept,
    became a strong critic of ‘moving’ magnetic
    field lines [Alfvén, 1976], especially in his
    later years. He warned against use of the
    concepts of ‘frozen-in’ and ‘moving’ magnetic
    field lines for the reasons that are
    emphasized above.
    The basic reason for these difficulties with
    ‘moving’ magnetic field lines is, of course,
    that motion of magnetic field lines is inherently
    meaningless. 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 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.
    As we have seen, such conventions are
    fraught with pitfalls and should only be used
    with utmost care lest they lead to erroneous
    conclusions. To paraphrase Ralph Nader,
    moving magnetic field lines are “unsafe at
    any speed.”

    As does Donald Scott:

    Real Properties of Electromagnetic Fields and Plasma in the Cosmos

    Alfvén [1] was explicit in his condemnation of the reconnecting
    concept: “Of course there can be no magnetic merging
    energy transfer. The most important criticism of the merging
    mechanism is that by Heikkila [21], who, with increasing
    strength, has demonstrated that it is wrong. In spite of all
    this, we have witnessed, at the same time, an enormously
    voluminous formalism building up based on this obviously
    erroneous concept.

    Hannes Alfvén, a Nobel Laureate, being the founding father of MHD theory that magnetic reconnection is predicated on.

    This leaves us with two competing models to describe the function of the Aurora and other astrophysical plasmas, one being based on a theory that violates known laws of physics, the other being based on known properties of conducting plasmas.
    Last edited: Jan 21, 2009
  2. jcsd
  3. Nereid

    Nereid 4,014
    Staff Emeritus
    Science Advisor
    Gold Member

    Interesting post, Suede.

    I wonder ... to what extent is the disagreement merely one of appearance?

    I mean, plasmas behave the way they do (as we learn from experiment and observation), and theories are developed to account for the observed behaviours.

    It is possible, and to some extent even easy, to develop two theories that are equivalent ... in the sense that there is no experiment or observation which could distinguish between the two, even in principle*.

    In this case, perhaps there are two different ways to look at the bulk properties and behaviours of plasmas that are indistinguishable in terms of any experiment or observation?

    If so, the choice of which one to use is a matter of practicality, convenience, history, or whatever ... but not of physics.

    After all, plasmas are composed of particles - charged and uncharged - and so the only 'true' description of their behaviour must be one built on QED, mustn't it? And any physics of plasmas which does not show, explicitly, how it is compatible with QED in the appropriate limit must necessarily be incomplete (at best), mustn't it?

    * for a discussion of this kind of equivalence, in terms of 'expanding universe' vs 'shrinking universe', see here.

  4. my opinion:

    What I think will happen, is over time 'magnetic reconnection' will evolve from a theory that is incompatible with standard plasma physics to one that is compatible.

    What they call a "reconnection event" will replace "exploding double layer" but will mean the same thing as an exploding double layer.

    I don’t think classical plasma physics is too far removed from QED theory. Classical plasma physics starts at the level of the electron and works its way up to macro scale structures. So what you have is a direct unification between classical electrodynamics and the macro scale universe.

    QED, from what I understand of it, deals mostly in theory below the scale of the electron. If we have, starting at the level of the electron, a working model that can accurately depict and describe macro scale events based on electrical interactions, I think that would put us at a better standing than we are at now.
  5. It would be nice if you could show in detail that the regions in which reconnection happens can be correctly described by an "exploding double layer".

    At the moment the observations by e.g. Cluster are so good and in agreement with the theoretical description of reconnection, with the inward motion of "field lines" the energization of particles, the Hall current signature because of the decoupling of the ions from the field. I would look up the observations described by Sergeev et al (and refs therein).

    Also there is the interesting paper by Treumann et al. about the role of the Hall field.

    Although I did my PhD on double layers in astrophysics (mentioned in the Wiki page which is greatly rewritten by me with help from my predecessors, in its current and excellent form), I cannot see how a DL can make all the things that are observed near a reconnection region.

    But please show me with data and a model how it works.
  6. Just some random comments on your first post:

    Naturally there is a current in the system because reconnection happens in oppositely directed magnetic fields and through Maxwell's equations it is clear that these are two fields are separated by a current sheet, just like in nature in e.g. the Earth's magnetotail.

    electric fields must complete a circuit to flow?
    I do hope this is a language problem, because electric fields don't flow.

    Field aligne electric fields and field aligned currents have absolutely nothing to do with reconnection, so you cannot use that to claim that reconnecting is correct or not. Take a look at my paper here where the motion of the magnetic field is the cause of currents flowing. Something (which you will see I leave to the reader to decide what, reconnection, current disruption,...) sets plasma flows in motion, which is pulled along with the magnetic field (in the tail the frozen in condition is very well satisfied, determined from measurements not assumptions) As there is a barrier this motion needs to be stopped and one of the main ways of stopping is cross tail currents, and these close as field aligned currents.

    Now these field aligned currents, when they go through a region of low density, they need to be accelerated to maintain the current, which is usually done by a double layer.

    But from your description above, it sounds like you have no idea what a DL is.

    And I am insulted! You forget my paper on solitary kinetic Alfvén waves which carry parallel electric field in the auroral zone, and there is the paper by Chust et al which shows strong parallel E-fields measured by Freja and shows that they are real and no artifact.

    However, all these double layers and parallel electric fields are mainly close to the Earth, most of them in the auroral zone, whereas reconnection happens rather far down the tail (20 Earth radii) or near the nose of the magnetosphere.

  7. Just search for 'double layer' 'aurora' 'birkeland current' 'parallel electric field' in any geophysical journal.

    I turned up a bucket load with just a few simple searches.

    I'm not sure what kind of data and model you're looking for.

    Double layers in the downward current region of the aurora

    Parallel electric fields in the upward current region of the aurora: Numerical solutions

    Particle Simulation of Auroral Double Layers
    A double layer is that solution which preserves gross quasineutrality within its volume while permitting momentum balance between incident accelerated particles. The potential of the double layer is limited by the ion kinetic energy but need not match the global potential required for overall charge neutrality. One and two dimensional electrostatic particle simulations verify both double layer solutions and dependence of potentials on the injected energy. The difference between global and local potentials is absorbed in a sheath opposite the injection boundary. Potential formations are strictly dependent on the self-consistent charge distributions they support. Microinstabilities cause changes in particle distributions. Double layer motion is associated with exchange of momentum between particles and these fields.

    Double layers
    The basic properties of electrostatic double layers observed in laboratory gaseous discharges are reviewed. Theoretical results from both macroscopic 4-fluid theory and microscopic, Vlasov, theory are described and found to be in fairly good agreement. Recent work on Penrose-stable double layers, as well as double layers with oblique electric and magnetic fields are described. Applications to Birkeland currents in the ionosphere are made. It was found that kilovolt potential which drops along the geomagnetic field can be produced in the topside ionosphere by double layers. Anomalous turbulent resistivity effects are unlikely to produce large parallel potential drops since that would lead to excessive heating of the ambient plasma. Since double layers are laminar structures they will not produce heat until the accelerated particles are stopped in the lower much denser E-layer.

    Large parallel electric fields in the upward current region of the aurora: Evidence for ambipolar effects

    Double layers on auroral field lines
    Time-stationary solutions to the Vlasov-Poisson equation for ion holes and double layers were examined along with particle simulations which pertain to recent observations of small amplitude (e phi)/t sub e approx. 1 electric field structures on auroral field lines. Both the time-stationary analysis and the simulations suggest that double layers evolve from holes in ion phase space when their amplitude reaches (e phi)/t sub e approx. 1. Multiple small amplitude double layers which are seen in long simulation systems and are seen to propagate past spacecraft may account for the acceleration of plasma sheet electrons to produce the discrete aurora.

  8. A double layer can "explode" at any point and we have evidence for their existence throughout the magnetosphere of earth. I do indeed know what a double layer is, in fact I quoted the dictionary definition of one.

    If you want to believe magnetic field lines are real physical objects that merge and reconnect I suppose that's your business.

    I personally prefer Alfven's opinion.
    Last edited: Jan 23, 2009
    24 July 2008

    Surprise sequence

    Strung out like a line of buoys in the ocean, THEMIS tracked the true sequence of events. The outermost satellites registered a reconnection, an aurora appeared near Earth, then the inner probes saw a current disruption. This sequence was a surprise, as researchers expected the aurora to occur last.

    I'll tell you why it's a "suprise".

    Magentic reconnection isn't real and the models are wrong.

    That's a pretty huge suprise btw. That's like predicting: egg first splaters, then hammer falls.
    Last edited: Jan 23, 2009
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