order to sustain a plasma for any length of time. Any termination of

the input will cause the plasma to recombine back into a neutral gas and

any ‘walling off’ of a plasma from its power source will cause it to

recombine back into a neutral gas.’

Not always true. Again, raising the temperature high enough will ionize a gas without applying an voltage drop.”

There are four known types of fundamental forces in the universe:

Gravitational

Electromagnetic

Strong Nuclear

Weak Nuclear

Temperature in a plasma is a manifestation of time-varying of electrical forces, not gravitational or nuclear forces. The connection with heat and electricity is quite clear, and it is clear that a temperature gradient superimposed onto a plasma will disperse electrons and ions. Electrons are generally lighter than ions, so a temperature gradient can temporarily generate a voltage gradient. Similarly, applying a voltage to a plasma can easily produce temporary heating due to the separation of charges they impose.

“When the current structure is thin enough to compare with the ion

gyroradius, the assumptions that justify MHD no longer hold, and you

have a region of large dissipation – or as in terms of my previous

comments, the diffusion timescale is no long much much longer than the

convection timescale.”

“….”

“Inside the fully-self consistent current sheet, the assumptions that

justify the use of MHD break down, and therefore kinetic theory must be

used.”

Doesn’t that suggest that concerns critical of the scientific paradigm of MHD may in face be well-justified concerns? I suppose it is a difference in attitude. The cynical outsider might say that this issue disproves or discredits MHD, while people of the scientific academia may just see this as an area where “one model is invalid, so a different one is used”, whether or not the model can be considered to be a model belonging to MHD.

Of course, Mr. “Suede” is not differentiating between different levels of developments in MHD, and nor does he seem to think of MHD as “a paradigm with many models”, models which can, of course, “disagree” with one another, which usually is the result of being applicable for different parameter spaces. We would of course encounter those people who would prefer a model that describes the behavior of plasma across the complete range of parameter spaces, but usually something like that is found in a later period in the history of science. In some ways I admire the attempts to disregard models that are invalid in some parameter spaces, though at the same time I realize that science does not always cover all the bases on day one, and we likely will only find approximations. Nevertheless, it would seem more elegant to some (including myself) to see one model for plasmas consisting of all the possible special case scenarios, as opposed to many models for plasmas with each one being varied from the other.

]]>http://tallbloke.wordpress.com

There’s going to be a lot of pulped textbooks….

]]>“In conclusion, it seems that astrophysics is too important to be left in the hands of theoretical astrophysicists who have gotten their education from the listed textbooks. The multibillion dollar space data from astronomical telescopes should be treated by scientists who are familiar with laboratory and magnetospheric physics, circuit theory, and, of course, modern plasma physics. More than 99 percent of the Universe consists of plasma, and the ratio between electromagnetic and gravitational forces is 10 to-the-power-of 39.”

– H. Alfvén, NASA Conference Publication 2469, 1986, p. 16.”

]]>— This is not always true. Raising the temperature will ionize the gas; no “electrical input” necessary. (If by “electrical input”, you mean setting up a potential difference, which is what happens in the set up you describe above, then sure, the resulting currents will ionize the gas.)

“Because plasma is composed directly of negative electrons and positive ions, the gas is nearly super conductive. It is one of the best known conductors of electricity in the universe. Plasma also has a few other properties that we need to describe; in particular, plasma is very cellular in nature. That is to say, differing regions of plasma will wall themselves off from each other and form a boundary between themselves called a double layer.”

— Not always true, either. A highly collisonal plasma will exhibit high resistivity. And a double-layer only forms if the current within the plasma are greater than a certain threshold, called the Bohm current, which is physically the maximum amount of current that may be carried by the plasma.

“The quasineutrality of a plasma requires that plasma currents close on themselves in electric circuits.”

— Not true. Quasineutrality does not imply closed currents. A current is the difference between the motions of the positive ions and negative electrons. Jackson Electrodynamics (the standard graduate Electrodynamics textbook), explains why J = qV for a single ion or electron is incorrect. Charge continuity is d/dt (charge) + divergence of the current = 0; currents only close if the time rate of change of charges is zero, leaving div J = 0.

” If all the charged particles in a plasma were to stop moving completely, there would be no magnetic field.”

— What about an externally applied magnetic field? You can place

“Let us be clear, a constant source of electrical input is required in order to sustain a plasma for any length of time. Any termination of the input will cause the plasma to recombine back into a neutral gas and any ‘walling off’ of a plasma from its power source will cause it to recombine back into a neutral gas.”

— Not always true. Again, raising the temperature high enough will ionize a gas without applying an voltage drop.

“Plasma is a messy thing to model.”

— VERY TRUE!

“Because plasma is so incredibly messy to model, physicists employ some “tricks” to make the process easier to deal with.”

— Such “tricks” are justified depending on the situation under study.

“In order to make the process of modeling plasma manageable, scientists treat the plasma as a perfectly conductive fluid with zero resistance. That is to say, they treat the plasma as if the magnetic fields created by the electrical currents in the plasma are simply frozen into the plasma itself and remove any mention of the electrical currents necessary to create and maintain them.”

— Not always true. Only when they can be mathematically justified. Ideal MHD is only employed to describe plasmas in which the characteristic lengthscale is much much larger than the ion gyroradius, the characteristic timescales is much much longer than the plasma frequency, and the diffusion timescale is much much longer than the convection timescale. By representing all of plasma physics as being studied by Ideal MHD, you betray your utter ignorance of the science; you are clearly unaware of the Kilmontovitch equation, the Boltzman equation, the Vlasov equation, the moments of the Boltzman and the Vlasov equations, and multi-species fluid models.

“Obviously this violates Maxwell’s equations which state that in order to have a magnetic field in a plasma, one must have an electrical current flowing through it to produce the magnetic field in the first place. If all the electrons in a plasma were actually frozen into the plasma, there would be no magnetic fields because there would be no moving electrons.”

— This is wrong. Electrons are *NOT* the current carriers in a plasma. Again, a current is defined as the *DIFFERENCE* between the motions of the ions and electrons; electrons carry the current in a wire because the ions are bound together in a lattice, and the electrons are the only particles that move. In a plasma, *BOTH* electrons and ions move.

This treatment of the plasma as a perfectly conductive fluid with ‘frozen-in’ magnetic fields is called magnetohydrodynamic theory (MHD).”

— Not true. MHD is only the fluid treatment of a plasma; MHD does not differentiate between ions and electrons. IDEAL MHD describes a perfectly conductive fluid. RESISTIVE MHD describes an electrically resistive fluid.

“In reality, plasma itself is never perfectly conductive.”

— True.

“Because it must obey circuit laws, there is always some resistance, which therefore means there is always some current flowing with any given plasma.”

— This statement is not logically consistent. Plasma resistivity follows from the specific form of the particle collision integral in the Boltzman equation. Resistance does not imply currents; currents do not imply resistance. The transport of energy from macro-to-micro scales is a property of the plasma, regardless of whether or not currents are flowing.

“The elimination of the electrical currents allows physicists to model the plasma’s magnetic fields in a much simpler fashion. It is from these models of plasma that magnetic reconnection theory was born.”

— Wrong! Reconnection theory requires a dissipation region in which currents are flowing. Reconnection theory *NEVER* eliminated currents.

“The reason why plasma forms double layers can only be described by circuit theory using a resistive plasma that has an electrical current flowing through it. To be clear, MHD theory is incapable of accounting for WHY a double layer should form in a plasma. It, at best, can only describe it as a geometrical construct.”

— Classic double-layers are a well known, well studied, well described phenomenon. No plasma physicist ever describes double-layers with single-fluid MHD, because they require a charge separation. The simplest framework that can describe a double-layer is a two-fluid model, accounting for ions and electrons separately.

“The same is true of all MHD models of “magnetic reconnection.” In MHD theory, there is no explanation of why two parcels of plasma should suddenly decide to create a resistive barrier between themselves and experience an explosive release of energy.”

— Not true. MHD models of reconnection only require a resistive dissipation term in the induction equation – a term well justified by Ohm’s Law. In your scenario, the voltage difference, and therefore the currents, set up between different plasma parcels (which by the way, are arbitrarily differentiated from the background plasma) is perpendicular to the currents in reconnection.

“All models of MHD reconnection can be considered classic reification of theory. That is to say, they all treat the models as if they are representative of what is actually occurring in physical reality. In reality, FIRST one must have an electric current BEFORE one can have a magnetic field. This relationship is entirely reversed in MHD theory. The idea of MHD is that magnetic fields can induce currents in a moving conductive fluid, which create forces on the fluid, and also change the magnetic field itself.”

— What about an externally applied magnetic field (applied and maintained by sources external to the plasma system under study)? In addition, MHD does NOT reverse this. MHD combines the equations of hydrodynamics, Maxwell’s equations, and two constituent transport relationships called Ohm’s Law and the thermodynamic equation of state, to close the system. This framework has 15 equations and 15 variables {rho, Vx, Vy, Vz, P, T, Bx, By, Bz, Ex, Ey, Ez, Jx, Jy, Jz}. One can use various equations to eliminate various variables (for example, the non-relativistic Ampere’s Law, J = curl B, eliminates the current variable in favor of the magnetic field in the dynamic equations; but the currents are still derived by taking the curl of the magnetic field solution). There is a big debate about whether to study a given system (that satisfies MHD’s required assumptions) in terms of electric fields and currents, or in terms of magnetic field and flow velocities. Either way, all information is still in the system. Information is lost, however, when taking the appropriate moments of the Boltzman (or Vlasov) equation to derive MHD, or the appropriate averages of the two-fluid equations.

“In the Sweet-Parker model of magnetic reconnection, the plasma is still basically treated as a perfectly conductive fluid. However, in order to describe the incredible speed at which “reconnection” (which is really nothing more than an exploding double layer) takes place, they must add back in ad hoc resistivity along the boundary of the two plasma parcels in order to create a mechanism that accelerates the electrons to observed rates. There is no mention of a double layer condition between two differing plasma parcels in MHD reconnection, something we know must exist from laboratory observations of plasma. There is no mention of a double layer because MHD theory is completely incapable of modeling such behavior. Only circuit theory can account for the mechanics of a double layer.”

— You’re right in that Sweet-Parker makes no mention of double-layers. Sweet-Parker is 50 years old. Of course, reconnection science has advanced far beyond the Sweet-Parker model. Reconnection is being researched using the full Boltzman equation, the Vlasov equation. Sweet-Parker makes no mention of electrons; never has. There is no mention of double layers because Sweet-Parker is a single fluid model – again, about 50 years old. In addition, reconnection is not double-layers.

“So in their models of Sweet-Parker reconnection, the physicists start off with two parcels of plasma sitting next to each other and then throw a sheet of electrical current between them. Why this current sheet should exist in a real resistive plasma according to their models is not clearly defined. They claim that the current sheet creates a region of resistive plasma around it which is necessary to account for why magnetic energy should be dissipated across the boundary of two plasma parcels, which themselves are generally assumed to be perfectly conductive. The resistivity is necessary because, in a perfectly conducting medium, a magnetic field passing through another magnetic field would do nothing to the field lines.”

— Wrong! The current sheet is fully self-consistent with a magnetic field that changes direction (remember, J = curl B). When the current structure is thin enough to compare with the ion gyroradius, the assumptions that justify MHD no longer hold, and you have a region of large dissipation – or as in terms of my previous comments, the diffusion timescale is no long much much longer than the convection timescale. So, the “boundary” between plasma parcels is actually a fully-self consistent current sheet required because the magnetic field changes direction over a very short distance. This “boundary” has NOTHING whatsoever to do with the plasma parcel properties. In your (mis)understanding of what is happening, plasma parcels should exhibit double-layer boundaries everywhere – not simply near the reconnection region.

“Why this plasma should be resistive and why this current sheet should exist within MHD theory is not readily explained. While they have explanations for incorporating them into their models, they would be perfectly happy NOT using them if that is what made their model meet with observation. The existence of the current sheet and a resistive region on the boundary of two plasma parcels is NOT something that the MHD model predicted should be there from the start. They are things that were thrown into the MHD model in an after-the-fact manner in order to get their models to meet with observation. ”

— Wrong! The current sheet is fully-consistent with a magnetic field that changes direction (again, J = curl B), and well described within the MHD framework.

“This resistivity-out-of-nowhere along the boundary of two plasma parcels is called “anomalous resistivity” and is claimed to be a consequence of scattering created by the current sheet that creates drag between the electrons and ions. Of course, this is ridiculous because the space plasma that they claim this “anomalous resistivity” occurs in are basically collisionless. It is necessary for them to concoct such “anomalous resistivity” because without it, their models don’t even come close to accurately matching the observed data.”

— Not true. Anomalous resistivity is simply a resistivity that is not described by the standard transport theory (i.e., it is not the Spitzer resistivity). Never is it anywhere stated “resistivity-out-of-nowhere”. Inside the fully-self consistent current sheet, the assumptions that justify the use of MHD break down, and therefore kinetic theory must be used.

As for your next few paragraphs about magnetic field lines. You’re correct. Of course, nobody believes field lines are substantial quantities. Field lines are constructed (invented by Michael Faraday) to illustrate the field structure. In addition, “reconnection” is a bad name for the phenomenon, because it conjures up the idea that the whole phenomenon rests on the idea of field lines. You are wrong, however, if you believe that the phenomenon we call reconnection, can not be described without invoking field lines. You are clearly unaware of amount of work that has been done researching the phenomenon.

But don’t take my word for it. Instead of blah blah’ing on the internet to people who don’t know what you are talking about, and are therefore easily impressed by the way you sound, why not take this entire blah blah, and write it up as a scientific paper (Abstract, introduction and background, computations, discussion, and conclusion). You keep whining about scientific censorship and suppression. Alfven’s papers, Flalthammer’s papers, Scott’s papers are ALL available, for ANY scientist to read and make use of. Of course, you’ll notice that none of the papers you keep quoting have very many citations – because, scientists who actually understand this science understand why these papers do not apply (or in Donald Scott’s case, understand that he is – correctly – refuting his own misunderstanding of the science). Instead of whining on the internet, submit your paper to the peer-reviewed Physics of Plasmas, or the Astrophysical Journal.

]]>Seriously- they need to write Basic Electrical Physics and Basic Chemistry into the Atronomy and Astrophysics courses worldwide. >.<

]]>“Pick a unique point in space. Measure the B field direction. Take a differential step in that direction. Measure the B field direction, take another step. Etc. That traces out a line. This is the definition of a magnetic field line, it’s perfectly clear, it ignores E fields by definition.”

Please explain how “a differential step in that direction. Measure the B field direction, take another step, Etc” can stretch, snap, or reconnect, eh? How does it store energy, and release it?

P.S. also said:

“If you want to talk about reconnection scenarios purely in terms of the fields, and never mentioning lines, you can do that—the physics is the same, you’re just hobbling your ability to describe it to humans.”

Please explain how your vector field stores and then explosively releases energy in what you believe ions and electrons in a vector field store and explosively release energy of that magnitude without particle annihilation, or forming double layers from opposing current sheets or Birkeland current filaments?

Sorry, your math may tie together, but your physics don’t. 😛

]]>http://plasma.colorado.edu/phys7810/articles/Falthammar_MovingFieldLines_2007.pdf

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