Plasma physics, MHD, Alfvén, etc

[Tim Thompson]

Because everything I've read "mainstream" and indeed most of the links you supplied above, imply some sort of magnetic mechanisms is causing the Coronal heating difference. So how it possible to have a magnetic field without an electrical field ... So why make it more complicated than needs be? Electricity is used to accelerate particles to solar wind speeds. We can see all the electrical signatures and then choose to ignore them??

The problem here is that you do not know enough to understand what you read, and so you seriously misinterpret it. The standard, mainstream physics certainly does use electric fields to accelerate the particles. But the electric fields that do the accelerating are derived from the time variable magnetic fields, essentially via Faraday's Law. And the time variable magnetic field is derived from the electric fields of the charged particles of the solar plasma via the equations of dynamo theory.

So the basic process goes like this.
(1) Plasma in motion creates time varying magnetic field.
(2) Time varying magnetic field creates electric field.
(3) Electric field accelerates particles.

All of the scientists studying this problem know this process very well, so there is no reason for them to repeat it to each other, in papers they write to communicate with each other. Their papers consistently cast the problem in terms of the magnetic field, because in this case it is the magnetic field which is fundamental, and not the electric field. The electric field that does the particle accelerating is derived from the magnetic field, not the other way around. And since the magnetic field is relatively easy to observe, we simply start with the observed magnetic field, and work from there.

That's cool if the problem you are working on is the acceleration of solar wind particles, or perhaps the heating of the stellar corona. However, if you are working on the problem of generating the magnetic field in the first place, then assuming its existence is obviously not cool. So, the scientists working on that problem have to start with the detailed structure of the plasma (temperature, pressure, velocity, composition & etc.), and then model the generated magnetic field (including the back-reaction of the plasma to the magnetic field that it generated on itself). This is a much harder problem to approach observationally, since so much of the solar interior has been invisible, prior to the advent of helioseismology.

Why??? I'm sure you are intelligent enough, unlike me, to work out the implications! I'm sure you are.

Perhaps you were thinking that mainstream science claims that magnetic fields occur in the absence of electric fields? That is possible, but not under any circumstances that we are dealing with here.

As you state above these are plausible theories, what’s so implausible about the electric Sun theory?

It is contradicted by observsation, since key elements required by it, which should be observable, are not in fact observed, despite the presence of instruments fully capable of making the observations (i.e., where is the current that powers the sun?). It is also contrary to common sense physics. There has to be an ultimate source of energy for all physical processes, and none is forthcoming in the electric sun theory.

How far could we have advanced if we "assumed" space was not electricaly neutral

The electrical neutrality of space is not an assumption, it is a direct observation. Why should we "assume" anything that we already know is contrary to observation?

[Moderator note: this thread was created by splitting posts from the ATM thread, The Electric Sun (so you will see some ATM ideas and references).

The posts here are not, primarily, on the ATM idea, the electric Sun, but refer mostly to basic plasma physics, MHD (magneto-hydro dynamics), and the history of its development (especially the role of the contributions of Alfvén).

As there seems to be quite a bit of confusion, among some BAUT members, regarding plasma physics, I think this thread may help to clarify it, as well as provide an opportunity for BAUT members to ask questions about this area of modern physics.]

[Tim Thompson]

Regardless, there seems to be a contradiction between the statement above and a later statement from the same post?

There would be a contradiction only if you assume that electrical neutrality requires the complete absence of charged particles. But that is not the case. An electrically neutral plasma is one which has an equal number of positive & negative charge carriers. An electrically neutral plasma in motion will generate a magnetic field (this is an observed fact). The electrical neutrality of space is merely the observation that the number of positive & negative charge carriers is equal, not that they are absent.

[iantresman]

There would be a contradiction only if you assume that electrical neutrality requires the complete absence of charged particles. But that is not the case. An electrically neutral plasma is one which has an equal number of positive & negative charge carriers. An electrically neutral plasma in motion will generate a magnetic field (this is an observed fact). The electrical neutrality of space is merely the observation that the number of positive & negative charge carriers is equal, not that they are absent.

Can we all agree that space is (a) quasi-neutral (b) May contain charge separation regions (wherever there is a double layer)

Regards,
Ian Tresman

[upriver]

So the basic process goes like this.
(1) Plasma in motion creates time varying magnetic field.
(2) Time varying magnetic field creates electric field.
(3) Electric field accelerates particles.

The basic law is "A moving charge creates a magnetic field."
A single charge is/has an electric field.

A time varying magnetic field must cross a wire etc. to create a current flow.
Usually magnetic fields are talked about as being frozen into the plasma depending on the time scale. That means it moves with the plasma.

Plasma(charges, proton, electron, ion) in motion will usually have a driving potential. That would be a current, which is moving charges, which develop a magnetic field. So the magnetic field is a by product of electric field acceleration.

[tusenfem]

The basic law is "A moving charge creates a magnetic field."
A single charge is/has an electric field.

A time varying magnetic field must cross a wire etc. to create a current flow.
Usually magnetic fields are talked about as being frozen into the plasma depending on the time scale. That means it moves with the plasma.

Plasma(charges, proton, electron, ion) in motion will usually have a driving potential. That would be a current, which is moving charges, which develop a magnetic field. So the magnetic field is a by product of electric field acceleration.

A moving charge can be considered a current and thus produces a magnetic field. The charge is may move at constant velocity.
A single charge has an electric field around it, but as we are dealing with plasmas here, the single charge electric field does not extend over distances greater than the DeBije length. So, in all, single charge electric fields do not play a large role in the total plasma cloud, apart from creating the plasma frequency which is a collective behaviour of the plasma.

Time varying magnetic fields drive currents, also in a plasma. The fields do not have to cross a wire as the electric charges in the plasma are mobile enough and can set up currents.
Frozen in magnetic fields move with the plasma, indeed. This means that E+vxB=0, but if you look at Ohm's law you will see that there are many more terms than just this one. And uh, ... why are we discussing frozen in fields?

A driving potential is not a current, I can have a potential over empty space and not have a current. I need moving charges to have a current. Plasma in motion is just plasma in motion, e.g. in the sun's convective layer there is a temperature different, which makes the plasma well up in one channel and then down again in another channel, just like air circulation in the Earth's atmosphere.

So, now we get to the crux, it all depends on what scale you look at, just like Tim said above. If you look at the large scale there are the magnetic fields that are moving and changing in time. This time variation drives currents and electric fields via: curl(B) = mu0 J - epsilon0 dE/dt and dB/dt = - curl(E), Maxwell's equations that I hope are out of scrutiny (apart from me making mistakes in wher the mu0 and epsilon0 belong). So even if we have frozen in field, when we compress the plasma, the magnetic changes too via B2 = B1 * surf1 / surf2, where B1 and B2 are the magnetic fluxes through surfaces surf1 and surf2.

If you look at the microscopic physics of how magnetic fields are generated, you need to take another viewpoint, because then you get to the point that somewhere due to random motion of the plasma particles a mini-current is set up and creates a mini-magnetic field. This is a so-called seed field in the dynamo theory for the sun. If things are quiet, the field will contract and dissipate and nothing of it. If things are more turbulent, then we can have that the tiny magnetic loop gets sheared, and folded on itself, basically then doubling the field strength. If you do that often enough you can build up a considerable magnetic field. Naturally (I can see your comment coming, what about the current, you forget about the current) there will be currents that are creating this magnetic field, they will also increase.

So, in summary, I guess you have to be a little schizofrenic if you want to be a plasma(astro)physicist.

[PhantomWolf]

The basic law is "A moving charge creates a magnetic field."

But not all magnetic fields are created by moving charges.

Magnetic fields are created by the spin of the charge and when you align the spins on the electrons in an atom in a material you will produce a magnetic field. Electrons or protons moving in a uniform motion will align the spins, but you can align the electrons without a current, iron is very good at doing it, though other materials will do it as well.

The moral of this is while:

Current = Magnetic Field
Magnetic Field ≠ Current

[Thomas(believer)]

The basic law is "A moving charge creates a magnetic field."

But not all magnetic fields are created by moving charges.

Magnetic fields are created by the spin of the charge and when you align the spins on the electrons in an atom in a material you will produce a magnetic field. Electrons or protons moving in a uniform motion will align the spins, but you can align the electrons without a current, iron is very good at doing it, though other materials will do it as well.

The moral of this is while:

Current = Magnetic Field
Magnetic Field ≠ Current

Maybe a too simple thought of me, but isn't an electron with spin a moving charge? Or has electron-spin really nothing to do with motion?

[P.Asmah]

I doubt that any significant number of scientists, in the "modern" sense, ever believed that space was truly "empty".

Well, I thought it was expected to be a perfect vacuum not so long back, but we move on.

No doubt the idea of space being filled with charged particles has been batting about for the last 100 years or so. Surely over the last 50-60 years, space filled with charged particles has been the mainstream norm.

Sure, but it is the role and importance of these plasmas which is now under debate. EUrs, of course, go much further than the mainstream in this respect.

I am referring specifically to the solar wind; since we are on the electric sun topic, that's the relevant space & plasma.

OK

However, as a general rule, all space plasma that we can observe, is seen to behave globally as if it were charge neutral, though I should think there are bound to be charged currents flowing in small scale environments. One has to study these things on a case by case basis.

Careful, you almost uttered the words 'frozen in' there! Alfven debunked this idea. He was also the chap who came up with Magnetohydrodynamics BTW, despite you claim in another post that he was very down on the idea!

[tusenfem]

Careful, you almost uttered the words 'frozen in' there! Alfven debunked this idea. He was also the chap who came up with Magnetohydrodynamics BTW, despite you claim in another post that he was very down on the idea!

Sorry, old chap, but frozen in magnetic fields is a direct consequence of Alven's MHD assuming (almost) perfect conductivity. Or did you mean another "frozen in" as I see nowhere that Tim even remotely gets into the neighbourhood of being frozen.

* edited to correct an inaccuracy *

[P.Asmah]

Sorry, old chap, but frozen in magnetic fields is a direct consequence of Alven's MHD assuming (almost) perfect conductivity. Or did you mean another "frozen in" as I see nowhere that Tim even remotely gets into the neighbourhood of being frozen.

* edited to correct an inaccuracy *

He got pretty damned close to saying it, and that was my concern. And in another thread he made the bizarre claim that Alfven was somehow down on MHD, seemingly unaware that 'he wrote the book on it'! In fact he won his nobel prize for work in this area.

Anyway, this is what Alfven had to say about frozen in magnetic fields:

"The electrical conductivity of any material, including plasma, is determined by two factors: the density of the population of available charge carriers (the ions) in the material, and the mobility of these carriers. In any plasma, the mobility of the ions is extremely high. Electrons and ions can move around very freely in space. But the concentration of ions available to carry charge may not be at all high if the plasma is very low pressure or diffuse. In short, although plasmas are excellent conductors, they are not perfect. It therefore follows that weak electric fields can exist inside them, and magnetic fields are NOT frozen inside them."

[tusenfem]

However, as a general rule, all space plasma that we can observe, is seen to behave globally as if it were charge neutral, though I should think there are bound to be charged currents flowing in small scale environments. One has to study these things on a case by case basis.

He got pretty damned close to saying it, and that was my concern. And in another thread he made the bizarre claim that Alfven was somehow down on MHD, seemingly unaware that 'he wrote the book on it'! In fact he won his nobel prize for work in this area.

So Tim says that space plasmas can be considered charge neutral.
But he also says there may be currents in some regions.
No mention here of magnetic fields, not not even close to "frozen in's" nephew!

[Tim Thompson]

He got pretty damned close to saying it, and that was my concern. And in another thread he made the bizarre claim that Alfven was somehow down on MHD, seemingly unaware that 'he wrote the book on it'! In fact he won his nobel prize for work in this area.

I never said any such thing. What I did say, in this post, in this thread was this:

I think you will find that a rift deveolped between Alfven & the astrophysical community. It is not terribly unlike the rift that developed between Einstein and the physics community. Just as Einstein rejected much of quantum mechanics, so did Alfven reject much of magnetohydrodynamics. And just as the world of physics regretably left Einstein behind, so did the world of plasma astrophysics leave Alfven behind. And this does not detract in any way from the evident fact that both Einstein & Alfven contributed enormously to their fields of endeavor, and both received well earned Nobel Prizes (Einstein in 1921 and Alfven in 1970). Alfven continued to believe that non-neutral electric currents were responsible for much of the magnetic phenomena in the universe. He became essentially alone in this. In the passage you quote, Alfven is selling his own point, which most astrophysicists were in the process of rejecting.

I never suggested that Alfven did not invent magnetohydrodynamics. I have a few of Alfven's books, I have studied MHD, and I have even met Alfven myself. I am well aware of his role in the creation of MHD (although I will also point out that it is unfair to single out Alfven, and not even mention the contributions of people like Parker & Cowling, and others). But what I said was true nevertheless. Alfven did not remain loyal to MHD, but went off on his own. And that's a fact.

Alfven never in his life suggested that magnetic fields were not frozen in, that is a grave misconception held by those who chose to deify Alfven, instead of actually bothering to study the physics that Alfven presented. Whether or not a field is "forzen in" depends entirely on the conductivity of the plasma. The magnetic field is literally frozen in if the plasma is perfectly conducting, which Alfven himself conclusively proved. He also showed that the higher the resistivity of the plasma, the less "forzen in" the field would be.

You miss Alfven's point entirely. He showed that the resistivity of the plasma sets a characteristic time scale for magnetic field drift through the plasma. So, let us say that the drift time scale is 10⁹ years in some plasma. And now let us say that I want to know what's happening in that plasma, in a process that takes 10⁴ years. The time scale I am interested in is very short compared to the drift time scale, so I can safely assume that the magnetic field is forzen into the plasma, over the time scale of my study, with no ill consequences. But, if the drift time scale of that plasma were, say 10³ years, then I would be badly mistaken in assuming that the magnetic field were forzen in, because the drift time scale is short compared to my time scale of interest. Alfven knew all of this, and says so expilicitly in his books & papers. And, as a matter of fact, mainstream plasma astrophysicists today adhere to this rule, as Alfven laid it out. So there is no conflict between the way mainstream scientists treat frozen in magnetic fields, and the way Alfven said they should be treated. There is only a failure of most of Alfven's fans to understand what Alfven actually said.

Alfven's main problem was the tendency in theoretical MHD to assume perfect conductivity, simply because it is a lot easier to compute things. This is still done in studies of "ideal MHD", for the same reason. We learn most efficiently by coming to grips with the "easy" problems first, as they are approximations of the more difficult problems that do not include the approximations of ideal MHD. But most EUers seem to suffer from the misconception that ideal MHD is assumed by mainstreamers to be "real" MHD, so they rail against a ghost of their own invention.

[iantresman]

Alfven never in his life suggested that magnetic fields were not frozen in, that is a grave misconception held by those who chose to deify Alfven, instead of actually bothering to study the physics that Alfven presented. Whether or not a field is "forzen in" depends entirely on the conductivity of the plasma. The magnetic field is literally frozen in if the plasma is perfectly conducting, which Alfven himself conclusively proved. He also showed that the higher the resistivity of the plasma, the less "forzen in" the field would be.

Have I misunderstood the following:

In 1967 Alfvén [109] noted evidence for the presence of electric fields parallel to magnetic fields, implying that the electric conductivity is not infinite and the magnetic field lines are not “frozen in.” (Later Alfvén [110] recalled that the “frozen field” concept had given him headaches for several years.) In Stephen G. Brush, "Alfvén’s Programme in Solar System Physics" (1992)

Alfvén also published a paper whose abstract states:

The concepts of 'frozen-in magnetic field lines' and 'field-line reconnection', which are frequently used in discussions of the theory of the magnetosphere, have been criticized by Alfven and Falthammar (1971), by Heikkila (1973), and by Alfven (1975). In the present paper, it is demonstrated that both concepts are unnecessary and often misleading. The frozen-in concept is shown to belong to the pseudo-plasma formalism which is useful only in special cases. (From: Alfven, H., "On frozen-in field lines and field-line reconnection" 1967)

Alfvén also wrote:

I thought that the frozen-in concept was very good from a pedagogical point of view, and indeed it became very popular. In reality, however, it was not a good pedagogical concept but a dangerous "pseudopedagogical concept." By "pseudopedagogical" I mean a concept which makes you believe that you understand a phenomenon whereas in reality you have drastically misunderstood it.
[..]
At that time (1950) we already knew enough to understand that a frozen-in treatment of the magnetosphere was absurd. But I did not understand why the frozen-in concept was not applicable.
[..]
In 1963, Fälthammar and I published the second edition
of Cosmical Electrodynamics [12] together. [..] We analyzed the consequences of this in some detail, and demonstrated with a number of examples that in the presence of an E_|| the frozen-in model broke down. On [12, p. 191] we wrote:

"In low density plasmas the concept of frozen-in lines of force is questionable. The concept of frozen-in lines of force may be useful in solar physics where we have to do with high- and medium-density plasmas, but may be grossly misleading if applied to the magnetosphere of the earth. To plasma in interstellar space it should be applied with some care."

[..]
Since then I have stressed in a large number of papers the danger of using the frozen-in concept [..] The most important criticism of the "merging" mechanism of energy transfer is due to Heikkila [40] 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. Indeed, we have been burdened with a gigantic pseudoscience which penetrates large parts of cosmic plasma physics. (Alfven, Hannes, "Double layers and circuits in astrophysics" 1986)

Regards,
Ian Tresman

[P.Asmah]

I never suggested that Alfven did not invent magnetohydrodynamics. I have a few of Alfven's books, I have studied MHD, and I have even met Alfven myself. I am well aware of his role in the creation of MHD (although I will also point out that it is unfair to single out Alfven, and not even mention the contributions of people like Parker & Cowling, and others). But what I said was true nevertheless. Alfven did not remain loyal to MHD, but went off on his own. And that's a fact.

Fair enough. Thank you for clarifying this.

And thanks also to Ian for providing excellent references.

I think these varying interpretations of plasma behaviours are critical to our discussion here?

[Nereid]

[Moderator note: this thread was created by splitting posts from the ATM thread, The Electric Sun (so you will see some ATM ideas and references).

The posts here are not, primarily, on the ATM idea, the electric Sun, but refer mostly to basic plasma physics, MHD (magneto-hydro dynamics), and the history of its development (especially the role of the contributions of Alfvén).

As there seems to be quite a bit of confusion, among some BAUT members, regarding plasma physics, I think this thread may help to clarify it, as well as provide an opportunity for BAUT members to ask questions about this area of modern physics.]

(repeat of info contained in OP).

[Tim Thompson]

Well, it seems that the "discussion" went nowhere, once this thread was created by Nereid. Plasma physics is a topic that arises in some ATM ideas, but is not amenable to general or simplistic discussion, so it is not surprising that this thread did not advance. The topic is both physically & mathematically intense, and usually specific problems have to have specific answers tailored for them, and cannot be understood by means of the prosey approach that is typical of boards like this.

So, with that in mind, and anticipating that this thread will continue to remain silent, I would like to take the opportunity to list the few plasma physics books I have handy in my library, as possible resources for those who might wish to seek them out as references. They too are physically & mathematically intense, but books can still be read, and pondered over, and even those with a minimal relevant education can get something out of them. I present them in no particular order.

Plasma Astrophysics, Toshiki Tajima & Kazunari Shibata, Westview Press, 2002
Originally published by Addison-Wesley, 1997. As the title implies, this is a book which specializes in the applications of plasma physics to astrophysical problems. Topics include turbulence, structure formation & filaments, dynamo theory, MHD & magnetic reconnection, MHD instabilities & jets, intergalactic plasma, and the origin of cosmological magnetic fields.

The Physics of Plasmas, Boyd & Sanderson, Cambridge University Press, 2003.
A general textbook on plasma physics, not directed towards astrophysics in particular. Topics include particle transport in magnetized plasmas, ideal & resistive MHD, plasma waves, collisional & collisionless plasmas, plasma radiation, and non-linear plasma physics.

Magnetic Reconnection: MHD Theory and Applications, Priest & Forbes, Cambridge University Press, 2000.
As the title implies, the book deals with magnetohydrodynamics, and in particular with the phenomena of magentic reconnection. Topics include current sheet formation, magnetic annihilation, steady & unsteady reconnection, and applications in laboratories, solar physics, magnetospheric physics, astrophysics, and particle acceleration.

Nonlinear Magnetohydrodynamics, Deiter Biskamp, Cambridge Monographs on Plasma Physics, 1993 & 1997.
Topics primarily include instabilities, turbulence, disruptive processes, pinches, and solar flares.

Space Physics - An Introduction to Plasmas and Particles in the Heliosphere and Magnetospheres, May-Britt Kallenrode, Springer 2001 (2nd ed).
Deals exclusively with solar system plasma physics. Topics include MHD, plasma waves and kinetic theory, solar wind & heliosphere, solar, terrestial & planetary magnetospheres, solar-terrestrial interactions, and instrumentation.

And of some historical interest ...

Origins of Magnetospheric Physics, James A. Van Allen, Smisthonian Institution Press, 1983.
Van Allen was himself one of the pioneers of the study of solar system plasmas, and one of the early scientists to realize that space was filled with plasma. He recounts the history of how that science develops, from the beginning of the 20th century, up to the era of Earth orbiting satellites. A good way to find out who did what.

There are a lot more books & papers & journals, I just put down what I have handy. I find these books readable, current & authoritative. If you want to learn something real about plasma physics, you could do worse than start here.

[P.Asmah]

The new sticky thread at the top of 'Against the Mainstream' suggests that Alfven's plasma physics are very much in the mainstream. This is disingenuous. While some of his work is now accepted by the mainstream -- which is positive progress, granted -- it is VERY IMPORTANT to realise that many of his ideas are still very much outside it. The mainstream is yet to catch up with many of them. This situation will probably change, but it will take time.

For example, Alfven proposed the following hypotheses as a corollary to his lab work.

1. In 1937 Alfven proposed that our galaxy contained a large-scale magnetic field and that charged particles moved in spiral orbits within it, owing to forces exerted by the field. Plasma carried the electrical currents which create the magnetic field.

2. "In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents." Hannes Alfven

3. "Gravitational systems are the ashes of prior electrical systems." Hannes Alfven

To summarise, it seems unfortunate that the implications of his work for cosmology remain largely unrecognised!

Neried. Clearly your post to which I refer needs updating in the light of these facts.

[Nereid]

The new sticky thread at the top of 'Against the Mainstream' suggests that Alfven's plasma physics are very much in the mainstream. This is disingenuous. While some of his work is now accepted by the mainstream -- which is positive progress, granted -- it is VERY IMPORTANT to realise that many of his ideas are still very much outside it. The mainstream is yet to catch up with many of them. This situation will probably change, but it will take time.

For example, Alfven proposed the following hypotheses as a corollary to his lab work.

1. In 1937 Alfven proposed that our galaxy contained a large-scale magnetic field and that charged particles moved in spiral orbits within it, owing to forces exerted by the field. Plasma carried the electrical currents which create the magnetic field.

2. "In order to understand the phenomena in a certain plasma region, it is necessary to map not only the magnetic but also the electric field and the electric currents." Hannes Alfven

3. "Gravitational systems are the ashes of prior electrical systems." Hannes Alfven

To summarise, it seems unfortunate that the implications of his work for cosmology remain largely unrecognised!

Neried. Clearly your post to which I refer needs updating in the light of these facts.

If you wish to start a new ATM thread, on Alfvén ATM hypotheses, you are welcome to do so.

Please bear in mind that BAUT is an internet discussion forum focussed on astronomy, astrophysics, cosmology, and space science, and is avowedly scientific in its approach.

With regard to "Alfven's plasma physics", and this thread in the General Science section, this means those parts of his work, on plasma physics, which are in the mainstream today.

As you agree, I'm sure, we do not accept discussion of Newton's ideas concerning alchemy here in the General Science section of BAUT, because those ideas are most definitely against the mainstream. Similarly wrt various (a)ether theories, no matter what the record of the work of 19th century physicists who promoted these theories is.

[Housseinafghani]

Professores: Thank you all for this most informative discussion. Makes one realize that Gravitation is merely some form of magnetics.
And Further. Vermuch enjoyed the high level discussion.
Thanks
Houssein Afghani

[tusenfem]

Professores: Thank you all for this most informative discussion. Makes one realize that Gravitation is merely some form of magnetics.
And Further. Vermuch enjoyed the high level discussion.
Thanks
Houssein Afghani

Sorry, Houssein, but gravitation has nothing to do with magnetics, and it beats me how you got to this conclusion reading this thread.

[publiusr]

I seem to remember a Japanese naval vessel that used MHD. It didn't seem to go very fast.

[iantresman]

I seem to remember a Japanese naval vessel that used MHD. It didn't seem to go very fast.

The Magnetohydrodynamic drive. I suspect that it's advantage is that it is quiet.

Which reminds me of another non-mechanical plasma drive, the Hall Effect thruster, based on double layers. [ref]

[tusenfem]

The Magnetohydrodynamic drive. I suspect that it's advantage is that it is quiet.

Which reminds me of another non-mechanical plasma drive, the Hall Effect thruster, based on double layers. [ref]

A nice ion thruster mechanism, but how you get the hall effect in here, I did not see that mentioned.

[iantresman]

I guessed that was similar to the Hall Effect Thruster.