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 25th January 2012, 01:05 AM #6136 Tim Thompson Muse     Join Date: Dec 2008 Posts: 969 Plasma Physics: "E orientation" or "B orientation"? Unfortunately for Mozina, despite his extreme self-confidence, his understanding of physics in general is woefully inadequate to the task of carrying on a meaningful conversation on the topic in the presence of people who actually do know what they are talking about. His mistakes don't happen at the tricky cutting-edge of active research, they happen at the foundation of knowledge. His mistakes are fundamental and broadly conceptual, not necessarily mistakes in handling this or that detail. One of his favorite complaints, repeated constantly for years, is the idea of the "E orientation" versus the "B orientation", or the "electric" versus the "magnetic" orientation for understanding plasma physics. Here are a couple of representative remarks, highlighted emphasis added by me. From 2 December 2011 ... Originally Posted by Michael Mozina I'm not personally confused. It's an unnecessarily confusing term that is mostly related to the mainstream's aversion to any sort of CIRCUIT/CURRENT flow orientation to events in space. You dumb everything down to the B orientation even though it's the electric horse that does all the actual work, including "opening" those lines of (PLASMA) force. From 11 August 2011 ... Originally Posted by Michael Mozina You're attempting to DUMB DOWN an ELECTRICALLY DRIVEN process to the B orientation just so you can call the whole thing "magnetic reconnection". BS. This preference for the "electric" over the "magnetic" is a major and fundamental failure by Mozina, which by itself is probably sufficient to permanently cripple any ability to understand what's really happening throughout the discipline of plasma physics. It is certainly the major stumbling block to his ever appreciating what magnetic reconnection really is or really does. I addressed this failure some time ago, but with little effect. Again, I have added highlighting emphasis for this occasion. From 30 December 2009 ... Originally Posted by Tim Thompson Reference the book Magnetic Reconnection: MHD Theory and Applications by Eric Priest & Terry Forbes, Cambridge University Press, 2000. Magnetic reconnection is not induction. Here is the induction equation in a plasma as given in Priest & Forbes, page 5: (1) $\partial \boldsymbol B / \partial t = \nabla \times (\boldsymbol v \times \boldsymbol B) - \nabla \times (\eta \nabla \times \boldsymbol B)$ Here $\eta$ is the magnetic diffusivity. If $\eta$ is uniform then the induction equation reduces to ... (2) $\partial \boldsymbol B / \partial t = \nabla \times (\boldsymbol v \times \boldsymbol B) + \eta \nabla^2 \boldsymbol B$ { ... } Given the equation I have labeled (2) above, we find ... "This is the basic equation of magnetic behavior in MHD, and it determines B once v is known. In the electromagnetic theory of fixed conductors, the electric field and electric current are primary variables with the current driven by electric fields. in such a fixed system the magnetic field is a secondary variable derived from the currents. However, in MHD the basic physics is quite different, since the plasma velocity (v) and magnetic field (B) are the primary variables, determined by the induction equation and the equation of motion, while the resulting current density (j) and electric field (E) are secondary and may be deduced from equations (1.8) and (1.10a) if required (Parker, 1996)." Priest & Forbes, page 14. The conversion of magnetic energy into a current always operates on a time-scale characteristic of the system, and that time scale is controlled by the ability of the magnetic field to move through the conductor, in order to create a dB/dt term from which the current is generated. That time-scale in a plasma is rather different than it is for a fixed conductor. Here we find the real deal once again in Priest & Forbes: "In space physics the distinction between ideal and non-ideal processes is important because simple estimates imply that magnetic dissipation acts on a time-scale which is many orders of magnitude slower than the observed time-scale of dynamic phenomena. 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." Priest & Forbes, page 6 In the highlighted portion we see that Priest & Forbes, who surely know far more about plasma physics than does Mozina, directly contradict the claim that the "E orientation" should be favored. But they really don't explain why, at least not here. Here I will add another complementary set of comments from Eugene Parker, one of the foremost living plasma astrophysicists, where he makes the same point, but also explains why the "E orientation" is inferior, or in his words, "a curious notion". From the book Conversations on Electric and Magnetic Fields in the Cosmos by Eugene N. Parker, Princeton University Press 2007, chapter 3 "Magnetic Fields", section 3.1 "Basic Considerations", pages 25-26. Originally Posted by Eugene Parker, 2007 In the absence of magnetic charges, magnetic fields appear only in association with electric currents and in association with time varying electric fields, in the manner described by eqn. (1.6). In the laboratory we create static magnetic fields by driving an electric current through a coil of wire. The emf driving the current is the source of energy that creates the magnetic field, so the emf and the current are clearly the cause of the magnetic field. On the other hand, in the cosmos the deformation of the magnetic field embedded in the swirling plasma causes the flow of electric current in the plasma in the manner described by eqn. (1.6), because the energy that drives the current comes from the magnetic field. That is to say, 4πj is maintained close to the value c∇ X B by the fact that any deviation produces a ∂E/∂t that quickly provides an E that drives j to the required value. So in the cosmos the large scale currents are obliged to obey Ampere's law, 4πj = c∇ X B In view of the small but nonvanishing friction between the relative motions of the electrons and ions, there is a continuing trickle of energy from the field to the current to maintain the flow of current required by Ampere,from which it follows that the field is the continuing cause of the current and not vice versa. The curious popular notion that the electric current causes the magnetic fields in the cosmos has led to the even more curious notion that the electric current is the more fundamental variable. Then, since currents are driven by electric fields, it is declared that the fundamental variables are E and j. As already noted, the difficulty is that there are no tractable dynamical equations for E and j. The current is dynamically passive, consisting of no more than the tiny inertia of the electron conduction velocity, while, as we shall see, the stresses in the electric field are small to second order in v/c and quite negligible. The dynamics of the plasma - magnetic field system is driven by the magnetic stress and inertia and pressure of the plasma. So when we inform ourselves on real plasma physics, the true nature of Mozina's failure is exposed. The "E orientation" gets the physics backwards, and in many cases, it is not even a solvable, or "tractable" system. It is in fact Mozina who is working hard to dumb-down, to borrow his words, his own understanding of plasma physics by substituting his own ill-informed notions of amateur level plasma physics for real plasma physics, as it is practiced by real plasma physicists. It must be clearly understood that in astrophysical plasmas, in nearly all cases, the "B orientation" is absolutely correct, is the orientation that actually gets the physics right, and in many cases is the only way to understand the physics of the plasma at all. And be mindful of my earlier comment: Originally Posted by Tim Thompson All magnetic fields are originally generated by electric currents. However, while the current flows in a confined volume, the consequent magnetic field will fill a vastly larger volume than the current. Hence it is possible to measure an active and time variable magnetic field in a vacuum far removed from the current that generated it. This is a point which seems to be overlooked to me so I want to make sure the point is made explicitly somewhere. Furthermore, magnetic fields and plasmas commonly couple together, so that the plasma will carry the "frozen in" magnetic field with it. So a plasma can be magnetized by a magnetic field that is not generated by that plasma, but by another completely independent plasma far away. As an example, the solar wind carries the solar magnetic field along with it. The magnetic field was originally generated in the sun, but is carried to the outermost reaches of the solar system by the solar wind, which can deform that magnetic field, but has nothing to do with the generation of that magnetic field. Likewise, magnetic fields generated deep inside the sun will pass through the photosphere of the sun and couple with it, despite not being formed in the photosphere by the plasma it is coupled to. So it is important to understand that we can have a magnetic field in a plasma, but not assign the task of generating that magnetic field to that particular plasma. The sentence I have highlighted here illustrates the basic idea that is described in physical detail by Priest & Forbes and by Parker. Mozina seems to think that the local magnetic field must always be generated by the very same local plasma that it threads through, but this is certainly not the case in almost all astrophysical circumstances. The motion of the local magnetic field necessarily generates a time variable magnetic field, ∂B/∂t, which is the local source of the local energy that drives the currents in the local plasma. Mozina's preference for the "E orientation" is wrong and is a major stumbling block for him. As long as he holds to it, he prevents himself from ever understanding plasma physics & magnetic reconnection. __________________ The point of philosophy is to start with something so simple as not to seem worth stating, and to end with something so paradoxical that no one will believe it. -- Bertrand Russell