Peratt - Plasma Models

CraigS · #1 03-10-2010, 12:09 PM

Following on from the "Primordial Magnetic Fields" thread, I have started investigating Peratt's view of Plasma Models and Scaling.

Alex forwarded us a list of reading material and it would seem that the following paper is one of the seminal EU reference papers, upon which they build their views.

The paper is called:

"Advance in Numerical Modelling of Astrophysical and Space Plasmas"
it is fairly old, dated 1997, and is the first in a series of three papers.

As the version Alex(EU) forwarded us is in read-only PDF format, I unfortunately cannot cut and paste text here for comment. It is 3.3 MB so I can't upload it, either.

So, I have uploaded the first 3 pages with the Abstract and Intro included.

It does not start out well. Peratt seems to rule out the possibility that Space Plasmas can, or ever will, be able to be detected and proceeds from there. This basis would seem to be an extremely limiting way to start out any research reporting paper.

I have an open mind on this, and I may acquire further perspectives as I read on. There is a section on Synchrotron radiation which I look forward to reading.

Comments welcome.

Cheers

renormalised (Carl) · #2 03-10-2010, 12:46 PM

What journal was it in....I'll download it

renormalised (Carl) · #3 03-10-2010, 12:47 PM

Just reading what you posted there is giving me an idea of where the article is going.

The abstract was enough to tell me that Perrat has a limited understanding of both astrophysics and the methods/applications used to study plasma phenomena in space. In any case, this article is so far behind current technology in both its scale and application it's not funny. As for some of his contentions about the inability of not being able to observe the condition in the magnetospheres of the planets from Earth (or at least from satellites in orbit about the Earth or close by)....what a load of twaddle. Having spacecraft actually out there orbiting the planets is even better. Can't get more in situ than that. And, so far as the conditions are concerned at a distance from us (as he mentions, beyond a few parsecs), what are the bevvy of satellites (and even ground based instruments) doing up there?? What he conveniently forgets is that you don't have to go to the mountain in order to see what's there...the mountain comes to us (in the form of EM energy). If it was so hard to deduce what was happening (not saying it's easy, but it's not impossible), then we'd be no more the wiser than what we where 50 or more years ago.

He should stick to what he was trained for and knows best....industrial plasma physics.

Leave the space physics to those that know something about it.

CraigS · #4 03-10-2010, 12:49 PM

Link is:

http://public.lanl.gov/alp/plasma/do.../AdvancesI.pdf

renormalised (Carl) · #5 03-10-2010, 01:04 PM

Thanks

CraigS · #6 03-10-2010, 01:18 PM

He seems to quote space based plasma field strengths without providing any references as to the source of the information.

His intergalactic strengths seem to be overstated (strength-wise) compared with the more modern info we found in the Intergalactic Magnetic Fields thread ….

Its a marathon paper this one ..

Cheers

CraigS · #7 03-10-2010, 01:55 PM

4.1 Synchrotron Radiation:

".. the question of cosmic synchrotron radiation is closely connected with the physics and origin of cosmic rays and with gamma- and X ray astronomy." …

Hmmm ….

CraigS · #8 03-10-2010, 01:59 PM

4.2 Transition Radiation

"Even in the absence of a magnetic field, astrophysical plasmas are capable of producing polarized radiation and large scale radiation patterns having diffraction-like patterns. At cellular interfaces delineating astrophysical plasmas of differeing constituency, the passge of electrical currents can produce transition radiation, … produced by the propagation of charged particles through the interface between media with differing dielectric constants."

"Long a topic of theoretical interest, transition radiation has been experimentally verified in the far infrared…

Thus coherent transition radiation may give information about large scale cellular astrophysical transition regions…"

Hmm ..

renormalised (Carl) · #9 03-10-2010, 02:00 PM

There's a lot of misinformation in that paper...example..."No rotating object in the universe that is devoid of a magnetic fields is known" Wrong. What about Venus. It has no magnetic field, yet it rotates (very slowly). Mars is another. It doesn't have a planetary dynamo. It only has areas of weak magnetic fields which are mostly confined to cratered highlands and some basins in the southern hemisphere. They're relict fields from the time when the planet did have a dynamo (before 3.9Ga). And here's something to throw a spanner into the works...Ganymede is tidally locked with Jupiter. Yet it produces a magnetic field. On the basis of Perrat's contentions, go figure

The Sun's magnetic field is 1G (gauss), most stars over F4 have bugger all magnetic fields, if any at all. Only sunspots and the M class stars have fields anywhere near 3-4T in strength (and not all M class stars have fields that strong, only the flare stars).

His other field strengths, especially the IGMF are off by several orders of magnitude, as are his galactic fields.

Space is not a vacuum (he wants to go and learn the definition of the term).

And that is just the start!!!.

renormalised (Carl) · #10 03-10-2010, 02:05 PM

Quote:

Originally Posted by CraigS

4.1 Synchrotron Radiation:

".. the question of cosmic synchrotron radiation is closely connected with the physics and origin of cosmic rays and with gamma- and X ray astronomy." …

Hmmm ….

Cosmic rays can be generated in a number of ways, but aren't necessarily tied to the origin of synchrotron radiation. Same with gamma and x ray sources. Yes, the are related in some instances, but not necessarily with every case.

CraigS · #11 03-10-2010, 02:13 PM

Quote:

Originally Posted by renormalised

There's a lot of misinformation in that paper...example..."No rotating object in the universe that is devoid of a magnetic fields is known" Wrong. What about Venus. It has no magnetic field, yet it rotates (very slowly). Mars is another. It doesn't have a planetary dynamo. It only has areas of weak magnetic fields which are mostly confined to cratered highlands and some basins in the southern hemisphere. They're relict fields from the time when the planet did have a dynamo (before 3.9Ga). And here's something to throw a spanner into the works...Ganymede is tidally locked with Jupiter. Yet it produces a magnetic field. On the basis of Perrat's contentions, go figure

The Sun's magnetic field is 1G (gauss), most stars over F4 have bugger all magnetic fields, if any at all. Only sunspots and the M class stars have fields anywhere near 3-4T in strength (and not all M class stars have fields that strong, only the flare stars).

His other field strengths, especially the IGMF are off by several orders of magnitude, as are his galactic fields.

Space is not a vacuum (he wants to go and learn the definition of the term).

And that is just the start!!!.

Yep. I agree with everything you say here.
Further on, he gets back into his area of expertise. Seems whenever he drops back into Astrophysical phenomena, things get wobbly and there are no references to real measurements. (Remember this is an old paper, so I assume most of the numbers are guesses)..

Cheers

renormalised (Carl) · #12 03-10-2010, 02:18 PM

But even back then, most astrophysicists knew the numbers (or most of them) that he was referring to, in so far as their actual values and such were concerned. They even knew much of the observational evidence. It wouldn't have taken too much to read up on it and quote it without making too many mistakes.

renormalised (Carl) · #13 03-10-2010, 02:37 PM

Another mistake....Titan doesn't have a magnetosphere. The only moon in the solar system that does is Ganymede, and it's very weak.

His "astrophysical" sections are rather weak, barely any information at all that is really of any relevance to anything else he talks about later on with regard to plasmas, which is mostly coming from his background in experimental and industrial plasma physics.

renormalised (Carl) · #14 03-10-2010, 02:51 PM

Here's another furphy...

"The nuclear core of the Sun is a plasma at a temperature of about 1.5KeV (true...that equates to around 15.5 Million K, which is just a little short of the true value, 15.7MK)."

" Beyond this, our knowledge about the Sun's interior is highly uncertain. Processes which govern the abundance of elements, nuclear reactions, and the generation of and the strength of the interior magnetic fields, are incompletely known." Whilst they're not fully understood, we understand and know a lot more about it than what he is claiming. Far more. How do we know this....from observations and mathematical modeling of the characteristics of the behaviour of gases (plasmas) under the conditions that are present within stars. We know what elements are there and how abundant they are, their proportions cf. to the major constituents of the stars, the nuclear reaction rates for the various nuclear processes that occur within stars, the EOS for the regions present within the stars and how these relate to the gas laws and the laws of thermodynamics, MHD and how these tie in with the generation of the magnetic fields of stars.

What Perrat should do is instead of quoting figures and getting theory mangled with respect to astrophysics, is actually go and do some courses or read the relevant literature and learn something about what he's talking about. Either that, or just stick with his field of speciality...industrial plasmas.

CraigS · #15 03-10-2010, 03:11 PM

As he goes thru the modelling he outlines:

"5.4 Issues in Simulating Cosmic Phenomena:
- boundary conditions;
- relativity;
- compression of time scales;
- collisions."

then he goes on to:

"-Gravitation
- Scaling Laws - the scaling of plasma physics on cosmical and laboratory scales generally involves estimates of diffusion in plasma, inertia forces acting on the currents, the Coriolis force, the gravitational force, the centrifugal force, and the j x B electromagnetic force …"

Then he goes on about needed tera-flop computers to run the simulations, distributed computing, modular code design, numerical modelling platforms, then he dives off into computer designs vs power, etc.

There seems to be six references in the "References" section to Astrophys, Space Sci, some Soviet Phys publications, heaps of iEEE Plasma Science references, Journal of Phys, etc.

A total of about 38 references in all.

And that's it.

Hmm .. he's trying to build a computer based model of plasmas in space.
Err…. yes … there are heaps of computer based models in the Astro Physics world. Nothing new ..

The conclusion is probably more intersting than this one.

Might skip to the end of paper #3.

Cheers

CraigS · #16 03-10-2010, 04:27 PM

Ok so now I'll move onto what seems to be the follow up paper ...
(WARNING: This paper is 8.3 MB mainly because it has colour photos in it .. not because it is long):

"Advances in Numerical Modelling of AstroPhysical and Space Plasmas"

'Part II Astrophysical Force Laws on the Large Scale'.
Published: APSS, 1998.

I realise Carl's too busy to read thru all this and provide his input (why expect him to anyway?). But this paper seems to talk about the results/outputs of the model discussed in the paper in my original post. He also gives the simulation results of a random assortment of double radio galaxies and quasars. Eg: he gives simulation derived parameters on the radiation properties of Cygnus A; Rotation velocity predictions of adjacent birkeland filaments and gets onto Spiral galaxy rotation velocities.

Hey Bojan … I found a circuit diagram on Page 60:

"Generic circuit description of a space plasma problem (in this case, the flow of Birkeland currents in the Earth's magnetosphere/ionosphere."

He goes on and assigns values in the subsequent text.

More bed-time reading.
(Yawn !).

Cheers

renormalised (Carl) · #17 03-10-2010, 05:22 PM

Oh Alex, just to preempt you....I don't have the time at present to look this paper over properly, so don't think what I wrote is some definitive critique. It's not...it's just some of the mistakes I caught from a quick glance at the thing. You're going to have to wait till I have the time to be bothered looking it over before you get a proper response to it (it is 71 pages long!!!).

CraigS · #18 04-10-2010, 01:27 PM

On the question of 'Dark Mode' currents, it would seem that Donald Scott (PhD, Electrical Engineering) is the one proposing it.

Scott - "Red and Brown Dwarfs".

I can't seem to find Peratt doing the same (from the papers). I'll keep looking.

Cheers

renormalised (Carl) · #19 04-10-2010, 02:13 PM

I wouldn't even bother with Scott's "analysis" of the evolution of stars considering he proposes that they're formed and powered by electrical currents "winding" through the galaxy!!!!

He should stick to electrical circuitry and microprocessors (which is his field).

He has little knowledge of astrophysics. Other than what he reads of the basics.

sjastro · #20 04-10-2010, 10:34 PM

Apart from the discrepancies raised by Carl and Craig, the definition of plasma is "nebulous" to say the least

Here is a quote from Peratt's article.

Quote:

The degree of ionization in interplanetary space and in other cosmic plasmas may vary over a wide range, from fullγ ionized to degrees of ionizatίon of only a fractiοn of a percent. Even weakly ionized plasma reacts strongly to electromagnetic fields since the ratiο of the electromagnetic force to the gravitatiοnal force is 39 orders of magnitude. For example, although the solar photospheric plasma has a degree of ionization as low as 10^-4, the major part of the condensable components is still largely ionίzed. The "neutral" hydrogen (HI) regions around galaxies are also plasmas, although the degree of ionization is only 10^-4.

The degree of ionization ordinarily relates to a gas not plasma.
As Peratt states in the last sentence the degree of ionization for HI regions is 10^-4. This means there is approximately 99% atomic hydrogen and 1% plasma. Yet he refers to the degree of ionization of plasmas. By definition a plasma is a gas that has been 100% ionized so referring to degrees of ionization of plasma seems to be illogical.

Peratt gets out of this logical bind by claiming that neutral hydrogen (HI) with it's 99% atomic hydrogen and 1% plasma is classified as a plasma!

Now here is the discrepancy. Plasma physicists study the reaction kinetics or collision cross-sections of plasmas and claim gases that have a degree of ionization as low as 10^-3 exhibit collision properties which a more plasma like.

Apart from the fact that HI regions fall below this value and are therefore not considered plasmas in terms of it's collision properties, Peratt seems to assume "the non plasma components" of the plasma are going to behave in the same way as plasma with regards to structure formation.

Would we expect a HI region composed of 99% neutral hydrogen to participate in the formation of Birkeland currents, magnetic fields, and be contrained in Z pinches?

It appears simply calling HI regions plasmas seems to get around the question.

Regards

Steven