Scientists improve ability to measure electrical properties of plasma

May 29, 2018 by Raphael Rosen, Princeton Plasma Physics Laboratory
Yevgeny Raitses and Brian Kraus in front of the Penning trap experiment, part of the Hall Trap Experiment, which was used to produce some of the experimental results. Credit: Elle Starkman

Any solid surface immersed within a plasma, including those in satellite engines and fusion reactors, is surrounded by a layer of electrical charge that determines the interaction between the surface and the plasma. Understanding the nature of this contact, which can affect the performance of the devices, often hinges on understanding how electrical charge is distributed around the surface. Now, recent research by scientists at the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL) indicates a way to more accurately measure these electrical properties.

The recent discovery relates to the layer, the so-called plasma-wall sheath of that surrounds objects, including diagnostic probes, inside the plasma, which is composed of charged electrons and ions. This layer protects probes by repelling other electrons in the plasma that affect the measurements of the instrument and sometimes even cause damage. "In effect, the object insulates itself from all these electrons in the plasma that carry energy and heat and could cause the probe to melt," said Brian Kraus, a graduate student in the Princeton Program in Plasma Physics who was lead author of the paper that published the findings in Physics of Plasmas.

Kraus and principal research physicist Yevgeny Raitses, co-author of the paper and research advisor for Kraus on his first-year graduate project, found that the layer's charge can sometimes be positive, contradicting what scientists have long thought—that the blanket always has a more negative charge than the surrounding plasma. The findings indicate that researchers must determine exactly what kind of charge surrounds the probe to be able to make corrections that will generate an accurate measurement of conditions inside the plasma.

Specifically, research conducted on the Raitses-led Hall Thruster Experiment (HTX) at PPPL, which is typically used to study for spacecraft and related plasma devices, showed that a heat-emitting diagnostic that is not connected to a grounded wire can sometimes produce the positive charge. The HTX was able to provide a steady, stable that let the scientists detect more precisely what kind of charge was building up next to the probe.

"The big new thing is that until now, scientists for at least a decade had been developing theoretical calculations and performing computational simulations showing that the positive layer, or inverse sheath, could occur, but no one had seen it in experiments involving probes," Kraus said. "In this paper, we say we think we are indeed seeing it in an experiment, as well as seeing the transition between negative and positive sheaths."

The research was the first to support these calculations concerning the effect of so-called highly emissive walls. Developing such calculations were Michael Campanell, Alexander Khrabrov, and Igor Kaganovich of PPPL, along with Dmytro Sydorenko at the University of Alberta. (Campanell is now at DOE's Lawrence Livermore National Laboratory.) The new experiments thus provide an excellent example of how theoretical predictions motivate experimental research that in turn validates theoretical predictions.

According to Raitses and Kraus, future research involving physical experiments will measure more carefully how well the highly emissive probe model matches observations. One such experiment would determine whether an emissive with a long wire would retain a more easily.

Explore further: Physicists to create new X-ray diagnostics for the WEST fusion device in France

More information: B. F. Kraus et al, Floating potential of emitting surfaces in plasmas with respect to the space potential, Physics of Plasmas (2018). DOI: 10.1063/1.5018335

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RealityCheck
2.3 / 5 (6) May 30, 2018
Now, as above latest insights demonstrate, we can now see better the reality phenomena because it is being increasingly studied/interpreted properly (as opposed to the old simplistic/incomplete theories and assumptions which some 'one-eyed' types here are still relying upon to indulge/perpetuate their personal feuds/insults agendas).

So, these latest insights should hopefully prompt all concerned to try and understand the complexity of plasma dynamics/contexts, and the 'self-sorting' and 'self-reinforcing' feedback which chaotically arise, evolve and subside within such phenomena. Yes?

Now, please can we have less of the longstanding personal silliness, and more of objective and courteous discussion of the reality unfolding under the noses of 'both one-eyed sides' in these petty feuds?

Be the better person/scientist, rather than continue being the nasty one-eyed asses working from long superseded simplistic interpretations/assumptions.

Good luck all. :)
cantdrive85
1.7 / 5 (6) May 30, 2018
Any solid surface immersed within a plasma, including those in satellite engines and fusion reactors, is surrounded by a layer of electrical charge that determines the interaction between the surface and the plasma.

The same can be said for objects in space plasmas too, it's why comets are electric. It's why the Universe is electric as 99.999% percent of everything is plasma.
cantdrive85
1.7 / 5 (6) May 30, 2018
The recent discovery relates to the layer, the so-called plasma-wall sheath of electrical charge that surrounds objects,

This is the double layer/sheath Alfvén described as being of utmost importance. These surfaces will arise between two plasmas as well.

The evidence to support the Electric Universe is being revealed on a daily basis. The Dark Ages of Science are being shown the light bit by bit.
cantdrive85
1 / 5 (4) May 30, 2018
"In effect, the object insulates itself from all these electrons in the plasma that carry energy and heat and could cause the probe to melt,"

LOL, I think I've heard this before...
cantdrive85
1 / 5 (4) Jun 01, 2018
A couple of downvotes but nary a comment. The behavior of the Dark Science acolytes is quite revealing, and amusing.
jonesdave
4 / 5 (4) Jun 01, 2018
The recent discovery relates to the layer, the so-called plasma-wall sheath of electrical charge that surrounds objects,

This is the double layer/sheath Alfvén described as being of utmost importance. These surfaces will arise between two plasmas as well.

The evidence to support the Electric Universe is being revealed on a daily basis. The Dark Ages of Science are being shown the light bit by bit.


Lol. The electric universe is a heap of crap, with no scientific validity. When did Earth orbit Saturn?
milnik
1 / 5 (2) Jun 01, 2018
If science makes such conclusions about the effect of the beach on objects around it, then science is gentle about what plasma is and how it arises and how it behaves.
Plasma is an energy state of matter that represents a mixture of electrons and positrons. It depends on who will surround the object immersed in plasma, whether the electrons or positive ions.
jonesdave
4 / 5 (4) Jun 01, 2018
Any solid surface immersed within a plasma, including those in satellite engines and fusion reactors, is surrounded by a layer of electrical charge that determines the interaction between the surface and the plasma.

The same can be said for objects in space plasmas too, it's why comets are electric. It's why the Universe is electric as 99.999% percent of everything is plasma.


Oh dear. Lol. Somebody has been on the EU kool-Aid! Comets are not electric, woo boy. As observed. No EDM (lol), no wandering arc discharges. Zilch. Everything EU predicted about comets has been wrong. Try again.
jonesdave
4 / 5 (4) Jun 01, 2018
The same can be said for objects in space plasmas too, it's why comets are electric.


Christ, what is this idiocy? Do you mean the comet that was landed on twice? And had no intrinsic magnetic field? Where do you get this crap? As if I didn't know!
Tell us woo boy, why would a comet, that is shielded from the solar wind for much of the time, due to outgassing, be electric, when an unshielded asteroid isn't? I can find you asteroids with similar orbital characteristics to JFC comets. Why are comets included in your woo, but asteroids aren't? Don't you people have anyone qualified beyond the level of idiot? You need to think these things through, before trying to con people with it.
gculpex
1 / 5 (3) Jun 01, 2018
The same can be said for objects in space plasmas too, it's why comets are electric.


Christ, what is this idiocy? Do you mean the comet that was landed on twice? And had no intrinsic magnetic field? Where do you get this crap? As if I didn't know!
Tell us woo boy, why would a comet, that is shielded from the solar wind for much of the time, due to outgassing, be electric, when an unshielded asteroid isn't? I can find you asteroids with similar orbital characteristics to JFC comets. Why are comets included in your woo, but asteroids aren't? Don't you people have anyone qualified beyond the level of idiot? You need to think these things through, before trying to con people with it.

What do you mean by 'shielded'? Can comets generate force fields?
Go back to your TV show if you're going to play fantasy.
jonesdave
5 / 5 (2) Jun 01, 2018
What do you mean by 'shielded'? Can comets generate force fields?
Go back to your TV show if you're going to play fantasy.


Lol. Another loon! It is shielded, dear boy, due to the fact that the solar wind is getting nowhere near the nucleus for long periods. That is due to the outgassing neutrals, mostly. At a certain point, the ion-neutral friction from those outgassing species causes the IMF to pile up, and therefore not even the magnetic field carried by the solar wind is reaching the nucleus. None of that applies at asteroids, which are just bare rock, subject to the solar wind and the IMF.
That is what I mean by 'shielded', as should have been obvious from what I wrote, or to anyone with even a passing knowledge of cometary environments.

gculpex
1 / 5 (3) Jun 01, 2018


At a certain point, the ion-neutral friction from those outgassing species causes the IMF to pile up, and therefore not even the magnetic field carried by the solar wind is reaching the nucleus. None of that applies at asteroids, which are just bare rock, subject to the solar wind and the IMF.


Why would a neutral be a gas?
what makes up a neutral?
You use the word 'ion' so the then the neutrals can't be neutral in charge.
You use the word friction as if particles (solar wind) can rub off large amounts of mass.
and lastly...
Where are your links to peer-reviewed papers?
jonesdave
5 / 5 (2) Jun 01, 2018


At a certain point, the ion-neutral friction from those outgassing species causes the IMF to pile up, and therefore not even the magnetic field carried by the solar wind is reaching the nucleus. None of that applies at asteroids, which are just bare rock, subject to the solar wind and the IMF.


Why would a neutral be a gas?
what makes up a neutral?
You use the word 'ion' so the then the neutrals can't be neutral in charge.
You use the word friction as if particles (solar wind) can rub off large amounts of mass.
and lastly...
Where are your links to peer-reviewed papers?


Oh dear God. Look up any paper that describes the cometary environment. The neutrals are mostly H2O. The lifetime against ionisation of H2O is ~ 10^6 secs. So, the vast bulk is neutrals.
Start here:

Cometary magnetospheres: a tutorial
Cravens, T. E. & Gombosi, T. I.
https://pdfs.sema...0720.pdf
cantdrive85
1.8 / 5 (5) Jun 02, 2018
The reason the SW is held at bay is due to the potential difference between the comet and the surrounding SW. The scientists in article above explain it as such;
"In effect, the object insulates itself..."
This is what the comet is doing, and the coma is the insulation, albeit leaky.
jonesdave
3.7 / 5 (3) Jun 02, 2018
The reason the SW is held at bay is due to the potential difference between the comet and the surrounding SW. The scientists in article above explain it as such;
"In effect, the object insulates itself..."
This is what the comet is doing, and the coma is the insulation, albeit leaky.


Wrong. There is no potential difference between the comet and the quasi-neutral solar wind. Idiot. Such a thing would be measured. And isn't. The paper is nothing to do with that. It is about a 1900 K cathode measuring dense plasmas in a frigging fusion device, loon! Completely irrelevant to comets. If you think differently, then quote the section of the paper that you think applies.
The SW is is excluded due to mass loading from cometary ions, from (mostly) H2O. As measured. That is why it isn't held off when there is little outgassing, and completely disappears when the rate is high. That is why there is no bow shock at asteroids. No volatiles to sublime.
cantdrive85
1.8 / 5 (5) Jun 02, 2018
jonesdumb insists plasma will not be plasma. That plasma is different from this plasma, plasma physics don't apply to space plasmas. Instead he believes in the hypothetical ideal gases of pre-space-age guesses. Needless to say, the plasma physics described above are relevant to all plasmas, just as the scientists above acknowledge.
That is why there is no bow shock at asteroids.

Most asteroids don't behave like comets because the asteroids charge differential to their environment isn't high enough to induce the reaction. However, some asteroids do behave like comets;
http://earthsky.o...r-shower
jonesdave
3.7 / 5 (3) Jun 02, 2018
^^^^^^^^What charge differential, dummy? Why is the solar wind reaching the comet? Why is it reaching an asteroid? Answer, thicko. And then answer why it stops reaching a comet, but carries on reaching an asteroid. God you lot are thick.
cantdrive85
1.8 / 5 (5) Jun 03, 2018
What charge differential

The charge differential established while the comet is far from the Sun where the particle density is much lower than nearer the Sun.
Why is the solar wind reaching the comet?

Because just as with most asteroids, there isn't enough of a charge differential of the comet due to the low charge density of the SW..
cantdrive85
1.7 / 5 (6) Jun 03, 2018
Why is it reaching an asteroid?

It has been "neutralized" with its environment, although it is still electric.
https://www.nasa....teroids/
And then answer why it stops reaching a comet, but carries on reaching an asteroid.

The charge density of the SW and the potential difference of the object vs the SW.
RealityCheck
1.6 / 5 (7) Jun 03, 2018
@jonesdave and @cantdrive.

A few days/weeks ago I mentioned a number of factors/processes which may result in localized electric/magnetic charge/fields feedbacks/structures at Comets. I forgot to mention that some factors/processes at Asteroids can also produce localized electric/magnetic phenomena there. One is the (by now well known) Photo-electric Effect; the other is the Photo-magnetization Effect (which you may not be familiar with as much as the Photo-Electric Effect). In the interests of your ongoing discussions (which could be more polite and less personally abusive), I post the following link to a more recent acknowledgement of the Photo-Electric Effect on many material surface layers (including Iron and Silicate Asteroid materials):

https://phys.org/...ion.html

RealityCheck
1.8 / 5 (5) Jun 03, 2018
ERRATA re my previous post....

The last part of the closing sentence should have read, in part...

"...more recent acknowledgement Photo-MAGNETIZING Effect..."

...and NOT "Photo-ELECTRIC Effect"

Apologies for typo. Thanks.
RNP
4.3 / 5 (6) Jun 04, 2018
@Realitycheck
In the name of all reason, what makes you think that a newly observed effect that takes place in a specially constructed compound could have significance in a comet or asteroid in which the required elements are almost nonexistant?
jonesdave
5 / 5 (5) Jun 04, 2018
Charging of bodies in space is nothing new. NASA have done sims to look at it on asteroids to guard against any possibility of damage to missions to such bodies. It is almost certainly happening on the Moon. This is caused by a combination of the PE effect and the solar wind. There is a whole plethora of scientific literature on this going back decades. The charges we are talking about are not going to cause any of the woo proposed by EU nutjobs. Do not forget that both Philae and Rosetta made it to the surface of 67P. Magnetic field? Zero.
RealityCheck
1.7 / 5 (6) Jun 04, 2018
@RNP.
In the name of all reason, what makes you think that a newly observed effect that takes place in a specially constructed compound could have significance in a comet or asteroid in which the required elements are almost nonexistant?
And, in like vein, in the name of objective science, will you please stop kneejerking from personal animus/bias; and just take the time to 'connect the dots' further afield than a specific experiment where the material chosen was something that gave a more robust signal for convenience and ease of observation/measurement etc. The same things happen all over on most materials because plasmonic phenomena acts to physically affect the 'particles' and 'properties/dynamics' thereof to varying degrees of 'robustness' of response/effect. In case you missed it all, I have long been pointing out all these kinds of 'surface/edge/interstitial' etc effects due to PLASMONIC (and related) phenomena called phonons, magnons, polaritons, excitons etc. :)
cantdrive85
1.8 / 5 (5) Jun 05, 2018
In the name of all reason, what makes you think that a newly observed effect that takes place in a specially constructed compound could have significance in a comet or asteroid in which the required elements are almost nonexistant?

The first sentence of the article explains it well enough;

"Any solid surface immersed within a plasma is surrounded by a layer of electrical charge that determines the interaction between the surface and the plasma."

It says "immersed in a plasma", it doesn't say "special plasmas". And if you cared to read the paper, they make it perfectly clear they are discussing all plasmas;

"Emissive sheaths are present in divertors, and scrape-off layers in magnetic fusion devices, around dust grains in laboratory and astrophysical plasmas, around satellites, in RF plasma processing devices, and around plasma probes. In all of these cases, the interplay between emitted and background plasmas determines the structure of sheath that forms"

jonesdave
not rated yet Jun 05, 2018
^^^^^^^^^And what were the properties of the plasma seen at and very close to the surface of a comet, from Rosetta and Philae? What sort of woo was happening? From actual observation and measurement?
gculpex
1 / 5 (1) Jun 05, 2018

https://pdfs.sema...0720.pdf


15 years ago? And this 'report' doesn't use the word 'shielded' but bow shock of the SW which would be correct. The system you are describing is static, not dynamic.

Stop adding to the article.
jonesdave
1 / 5 (1) Jun 05, 2018

https://pdfs.sema...0720.pdf


15 years ago? And this 'report' doesn't use the word 'shielded' but bow shock of the SW which would be correct. The system you are describing is static, not dynamic.

Stop adding to the article.


What are you blathering about? The solar wind does not reach the surface of a comet when it is most active. As observed. At Halley, at 67P and in artificial comet experiments. Type the words 'diamagnetic cavity; comets', into Google Scholar, and do some research. The solar wind does reach the surface when the comet is quiet, then it stops reaching it, and then it reaches it again as activity dies down. It is most certainly not a static system.
jonesdave
not rated yet Jun 05, 2018
Why is it reaching an asteroid?

It has been "neutralized" with its environment, although it is still electric.
https://www.nasa....teroids/
And then answer why it stops reaching a comet, but carries on reaching an asteroid.

The charge density of the SW and the potential difference of the object vs the SW.


What potential difference? Figures please. Why are asteroids on cometary orbits not behaving as comets? What is the difference? Why does a comet have a potential difference, and not an asteroid? Are they made of different material (yes!)? Why does the solar wind stop reaching the centre of a cloud of barium or lithium, in artificial comet experiments? No object to be seen. Only gas. Just like at real comets.
jonesdave
not rated yet Jun 05, 2018

https://pdfs.sema...0720.pdf


15 years ago? And this 'report' doesn't use the word 'shielded' but bow shock of the SW which would be correct. The system you are describing is static, not dynamic.

Stop adding to the article.


Here, perhaps this will help:

The plasma in the inner coma of comet Halley (within the "cometopause" which is located at a cometocentric distance of r = 10^5 km) was observed to be almost stationary and entirely of cometary
origin


https://agupubs.o...11p15025 (paywalled)

So, there you go, getting on for 100 000 km, and no more solar wind.
barakn
not rated yet Jun 05, 2018
In the name of all reason, what makes you think that a newly observed effect that takes place in a specially constructed compound could have significance in a comet or asteroid in which the required elements are almost nonexistant?

The first sentence of the article explains it well enough;

"Any solid surface immersed within a plasma is surrounded by a layer of electrical charge that determines the interaction between the surface and the plasma." -cantdrive85

Cantdrive85 is correct. Hannes Alfvén: "In a low density plasma, localized space charge regions may build up large potential drops over distances of the order of some tens of the Debye lengths." The Debye length of an object directly in the solar wind is about 10 m. Unfortunately, this scale is already too small compared to the size of a comet nucleus, let alone the entire coma.
barakn
1 / 5 (1) Jun 05, 2018
As hinted at by Alfvén, the Debye length is, roughly, inversely proportional to the square root of the density of ions and electrons. Because the area around an active comet contains much higher densities of electrons and ions than the solar wind, the Debye length will be much smaller than 10 m. With roughly 2000 charged species per cm^-3 near the surface, see https://arxiv.org...6745.pdf , the charge density is 1000 times larger than the solar wind, lowering the Debye Length to 32 cm. Per Alfven's "order of some tens of the Debye lengths," we'll take the sheath distance to be 10 m. As this is 7 orders of magnitude smaller than the 19,000 km long coma, the sheath region occupies a volume 21 orders of magnitude smaller than the volume of the coma (and that's being kind, because I've included the interior of the comet as part of the sheath). The sheath is completely inadequate to explain the size of the coma.
jonesdave
1 / 5 (1) Jun 05, 2018
^^^^^^^^It should also be noted that even at the largish heliocentric distances in this paper, the neutrals outnumber the plasma by ~ 1 million to 1. And also, when the solar wind and diamagnetic cavities form, the solar wind plasma is getting nowhere near the comet surface, as measured.
However, it will have access to asteroid surfaces. So absolutely no reason for them not to turn into comets, as per cantthink's 'logic'. Problem is, they don't.
jonesdave
1 / 5 (1) Jun 05, 2018
The main point to take away here, is that the reason the solar wind behaves as it does at comets, is due to mass loading from the ionised cometary volatiles. As has been known for a long time, and theorised for even longer. This cannot happen at an asteroid, of course, so the solar wind will have permanent access to the suface. The NASA simulation linked by CD shows that there is unlikely to be much to worry about, voltage wise. The same will apply at comets when they are inactive.
gculpex
not rated yet Jun 12, 2018


What are you blathering about? The solar wind does not reach the surface of a comet when it is most active. As observed. At Halley, at 67P, and in artificial comet experiments. Type the words 'diamagnetic cavity; comets', into Google Scholar, and do some research. The solar wind does reach the surface when the comet is quiet, then it stops reaching it, and then it reaches it again as activity dies down. It is most certainly not a static system.

In other words.. the comet fluctuates on and off like a firefly, LOL!!!!!

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