Lab takes detailed look at 2-D structure of turbulence in tokamaks

October 14, 2017, Princeton Plasma Physics Laboratory
Correlation analysis of three plasma discharges on NSTX for each of five different radial locations near the plasma edge. The red regions marked with a blue cross have high positive correlation around the origin point, while the blue regions marked with a yellow cross have high negative correlation. Credit: Stewart Zweben

A key hurdle for fusion researchers is understanding turbulence, the ripples and eddies that can cause the superhot plasma that fuels fusion reactions to leak heat and particles and keep fusion from taking place. Comprehending and reducing turbulence will facilitate the development of fusion as a safe, clean and abundant source of energy for generating electricity from power plants around the world.

At the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), scientists have assembled a large database of detailed measurements of the two dimensional (2-D) structure of edge made visible by a diagnostic technique known as gas puff imaging. The two dimensions, measured inside a fusion device called a tokamak, represent the radial and vertical structure of the turbulence.

Step toward fuller understanding

"This study is an incremental step toward a fuller understanding of turbulence," said physicist Stewart Zweben, lead author of the research published in the journal Physics of Plasmas. "It could help us understand how turbulence functions as the main cause of leakage of ."

Fusion occurs naturally in space, merging the light elements in plasma to release the energy that powers the sun and stars. On Earth, researchers create in facilities like tokamaks, which control the hot plasma with magnetic fields. But turbulence frequently causes heat to leak from its magnetic confinement.

PPPL scientists have now delved beyond previously published characterizations of turbulence and analyzed the data to focus on the 2-D spatial correlations within the turbulence. This correlation provides clues to the origin of the turbulent behavior that causes heat and particle leakage, and will serve as an additional basis for testing computer simulations of turbulence against empirical evidence.

Studying 20 discharges of plasma

The paper studied 20 discharges of plasma chosen as a representative sample of those created in PPPL's National Spherical Torus Experiment (NSTX) prior to its recent upgrade. In each of these discharges, a gas puff illuminated the turbulence near the edge of the plasma, where turbulence is of special interest. The puffs, a source of neutral atoms that glow in response to density changes within a well-defined region, allowed researchers to see fluctuations in the density of the turbulence. A fast camera recorded the resulting light at the rate of 400,000 frames per second over an image frame size of 64 pixels wide by 80 pixels high.

Zweben and co-authors performed computational analysis of the data from the camera, determining the correlations between different regions of the frames as the turbulent eddies moved through them. "We're observing the patterns of the spatial structure," Zweben said. "You can compare it to the structure of clouds drifting by. Some large clouds can be massed together or there can be a break with just plain sky."

Detailed view of turbulence

The correlations provide a detailed view of the nature of plasma turbulence. "Simple things about turbulence like its size and time scale have long been known," said PPPL physicist Daren Stotler, a coauthor of the paper. "These simulations take a deep dive into another level to look at how turbulence in one part of the plasma varies with respect to turbulence in another part."

In the resulting graphics, a blue cross indicates the point of focus for a calculation; the red and yellow areas around the cross are regions in which the turbulence is evolving similarly to the turbulence at the focal point. Farther away, researchers found regions in which the turbulence is changing opposite to the changes at the focal point. These farther-away regions are shown as shades of blue in the graphics, with the yellow cross indicating the point with the most negative correlation.

For example, if the red and yellow images were a region of high density turbulence, the blue images indicated low density. "The density increase must come from somewhere," said Zweben. "Maybe from the blue regions."

Going forward, knowledge of these correlations could be used to predict the behavior of turbulence in magnetically confined plasma. Success of the effort could deepen understanding of a fundamental cause of the loss of heat from .

Explore further: Researchers perform first basic-physics simulation of the impact of recycled atoms on plasma turbulence

More information: S. J. Zweben et al, Two-dimensional turbulence cross-correlation functions in the edge of NSTX, Physics of Plasmas (2017). DOI: 10.1063/1.5002695

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Chris_Reeve
Oct 14, 2017
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Chris_Reeve
Oct 14, 2017
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TopCat22
not rated yet Oct 15, 2017
Question I get from this is whether plasma can be caused to lase as in forming laser beam itself or a plasma beam. If so by having the plasma become polarised somehow through some mechanism if that would resolve the turbulence problem.

I remember hearing things like the Tesla death ray which sounds like polarisation or lasing of plasma may be a doable thing..

Just idle brain farts going on here and I have no knowledge or idea about this sort of a thing.
gculpex
5 / 5 (1) Oct 15, 2017
Question I get from this is whether plasma can be caused to lase as in forming laser beam itself or a plasma beam. If so by having the plasma become polarised somehow through some mechanism if that would resolve the turbulence problem.

I remember hearing things like the Tesla death ray which sounds like polarisation or lasing of plasma may be a doable thing..

Just idle brain farts going on here and I have no knowledge or idea about this sort of a thing.

Any idea that brings fusion to fruit is not off the table.
antialias_physorg
3 / 5 (4) Oct 15, 2017
Question I get from this is whether plasma can be caused to lase

Plasma is a state in which atoms are ionized (stripped of their electrons)

Laser light is the (stimulated) emission of photons from a medium. In that medium many electrons in atoms are 'pumped' to a higher energy level (creating an 'population invesion', where more electrons are in higher energy levels than in lower ones).
When another photon of the correct wavelength passes by the pumped electron falls back and emits another photon with the same wavelength (equal to difference in energy levels of the respective orbitals) and phase...which in turn can then cause another such process and so on, causing an avalanch effect an releasing a laser pulse.

So, no: Plasma cannot be made to lase. In one state (plasma) electrons are unbound while in a laser medium electrons must be bound.
retrosurf
not rated yet Oct 15, 2017
Of course plasma can lase.
As an example, consider the helium-neon gas laser,
a continuous DC current through a conductive plasma of helium and neon resulting in stimulated emission of coherent light.
antialias_physorg
3 / 5 (2) Oct 15, 2017
As an example, consider the helium-neon gas laser,

A gas is not the same as a plasma. In a He-Ne (or CO2 or other gas lasers) the atoms/molecules still retain their electrons. They are just pumped (e.g via flashlights or current) to a higher orbital - not stripped.
TheGhostofOtto1923
5 / 5 (2) Oct 15, 2017
Question I get from this is whether plasma can be caused to lase as in forming laser beam itself or a plasma beam
Well a little research would answer this question for you

"[The gain medium of a laser] can be of any state: gas, liquid, solid, or plasma."

And

"X-ray laser active media - The most often used media include highly ionized plasmas, created in a capillary discharge or when a linearly focused optical pulse hits a solid target."

- So you shouldn't be asking rank amateurs here to educate you or you are apt to get answers like
So, no: Plasma cannot be made to lase
TheGhostofOtto1923
5 / 5 (2) Oct 15, 2017
A gas is not the same as a plasma. In a He-Ne (or CO2 or other gas lasers) the atoms/molecules still retain their electrons
- And in addition to lasers, aa needs to learn a few things about plasma

"Based on the surrounding environmental temperature and density, partially ionised or fully ionised forms of plasma may be produced. Neon signs or lightning storms are examples of partially ionised plasma,[6] while the interior of the Sun is an example of fully ionised plasma,[7] along with the solar corona[8] and stars."

-before offering opinions on either. Or, like I and many other responsible posters here at physorg do, look something up before posting to make sure you know what you are talking about.
antialias_physorg
3 / 5 (2) Oct 15, 2017
Here's an explanation of how a gain medium works and what it can be (note that plasma is not among the gain media)
https://en.wikipe...r_medium

Even in x-ray lasers where the medium is partially ionized the actual lasing is produced by the atoms that have not been completely stripped and not the plasma ones (This requires atoms with high numbers of electrons)

In fusion reactors we're dealing with hydrogen plasma. Hydrogen has one electron. If it's a hydrogen plasma it's completely stripped. So, no: no lasing.

(Note that the *pumping* medium can be a plasma - from that in a flash lamp to a one created by a nuclear detonation. But that this not the medium that lases)

plasma become polarised somehow

What do you think the word 'polarise' means? (or should mean?).
Just throwing sciency words around is never a good idea unles you can explain what you mean.

TheGhostofOtto1923
5 / 5 (1) Oct 15, 2017
(note that plasma is not among the gain media)
"[The gain medium of a laser] can be of any state: gas, liquid, solid, or plasma."

haha
antialias_physorg
3 / 5 (2) Oct 15, 2017
The reason why plasma can't lase is because lasers have a very specific characteristic which is coherence (spatial, tempral - i.e. frequency).
For the coherece you need a defined jump in energy which releases a photons of all the same frequency.
In a plasma the energies are all over the place so you get a glow of all kinds of frequencies in a wide distribution.

However in atoms that have not been ionized the electrons are in very specific orbitals. A jump from a lower to a higher orbital requires a very specific energy in one go (this is what got Einstein his Nobel prize on the photoelectric effect, BTW). A jump from a higher to a lower orbital releases the same amount of energy. Atoms tend to want to have their lower orbitals filled, so usually nothing wild happens. But if you can pump a lot of electrons into defined upper orbitals (leaving a lower one free) and cause them to fall back down when stimulated (the 's' in the acronym LASER) you get laser light.
TheGhostofOtto1923
5 / 5 (2) Oct 15, 2017
However in atoms that have not been ionized the electrons are in very specific orbitals
uh partially ionized plasmas have cations with very specific orbitals

"A cation... is an ion with fewer electrons than protons, giving it a positive charge"

-I guess along with lasers and plasmas, aa needs to read up on ions as well. Yup, best to start from the beginning.

Knowing what cations and anions are certainly did help Einstein get his Nobel.
Chris_Reeve
Oct 15, 2017
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Chris_Reeve
Oct 15, 2017
This comment has been removed by a moderator.
TopCat22
not rated yet Oct 16, 2017
assuming then that plasma can lase then should this not eliminate (or reduce) the turbulence problem. A lasing plasma ray held to travel around in a magnetic field can keep getting energy added till fusion happens without turbulence collapsing the field.

This seems kind of an elementary solution but many times the smartest people do not see the forest for the trees.
antialias_physorg
3.7 / 5 (3) Oct 16, 2017
What is a "lasing plasma ray" supposed to be?
jeez, man...this is getting ridiculous.

Do you realize that what you're doing is the equivalent of going to a car enthusiast site and posting:
"If I crankshaft the sparkplug in my carbburator - will it make my wheels spin sideways?"

Yeah...there's a lot of car-technical terms in there...but it makes absolutely no sense.
TheGhostofOtto1923
not rated yet Oct 16, 2017
Do you realize that what you're doing is the equivalent of going to a car enthusiast site and posting:
"If I crankshaft the sparkplug in my carbburator - will it make my wheels spin sideways?"
Does aa know what he is doing?

"If I post in an erudite and pretentious enough manner I dont actually have to know what I am talking about or bother to look anything up and maybe convince people for instance that plasma lasers are not possible even though other posters have demonstrated that they are... and I never have to admit it when exposed because I am after all above that arent I?"

"pos·ture
verb
gerund or present participle: posturing
1.
behave in a way that is intended to impress or mislead others.
"a masking of fear with macho posturing"
synonyms: pose, strike an attitude, strut
"Keith postured, flexing his biceps"

-Strike a pose aa-
TheGhostofOtto1923
not rated yet Oct 16, 2017
Note that the 'pumping' medium can be a plasma... but that is not the one that lases.
Poor aa does not seem to know the difference between gain media and pumping media...

"The active laser medium (also called gain medium or lasing medium) is the source of optical gain within a laser. The gain results from the stimulated emission of electronic or molecular transitions to a lower energy state from a higher energy state previously populated by a pump source."

and

"[The gain medium of a laser] can be of any state: gas, liquid, solid, or plasma."

and

"Optical gain in the X-ray region can also be generated in plasmas, which themselves are typically created with laser beams or with electrical discharges. (The first such lasers were pumped with X-rays from nuclear explosions.)"

jeez, man...this is getting ridiculous.
TheGhostofOtto1923
not rated yet Oct 16, 2017
what the heck is a lasing plasma ray???
and/or
You can have an electron beam, or a proton beam. You cannot have a beam composed of both (plasma beam)
This is sort of that...

"An electrolaser is a type of electroshock weapon that is also a directed-energy weapon. It uses lasers to form an electrically conductive laser-induced plasma channel (LIPC). A fraction of a second later, a powerful electric current is sent down this plasma channel and delivered to the target..."
TheGhostofOtto1923
not rated yet Oct 16, 2017
"An electrolaser is a type of electroshock weapon that is also a directed-energy weapon. It uses lasers to form etcetc

The electric current isn't in the form of a "laser" due to the particle mass differential. He specifically asked if plasma can be lased, as in an analogue of a laser but composed of the charged particles which constitute a plasma. Yes, you can generate a plasma channel by lasing a medium with different potentials, but that formation is not a "plasma laser", it still takes the form of a bolt or arc. He wants laser like confinement/propagation of plasma...maybe someday we will have that ability....
He was not asking anything. He was talking gibberish.

Kind of like this:
Eventually, the plasma in a tokamek demonstrates a flow pattern in which the corresponding plasma generated field impinges on the fields generated by the tokamek...the result is particle and heat leakage as the particles now have another magnetic "route" they can follow
Source??
antialias_physorg
1 / 5 (1) Oct 16, 2017
It seems increasingly obvious that you guys don't really know how a laser works. Just look it up. Look up gain medium.
Look up population inversion.
Look up Boltzman distribution while you're at it.
(And when you did this look up what a plasma is and why it doesn't fit with the prerequisites)

There's really no point discussing this until you get up to speed.
TheGhostofOtto1923
not rated yet Oct 16, 2017
(And when you did this look up what a plasma is and why it doesn't fit with the prerequisites)
Try looking up this:

"ref·er·ence
ˈref(ə)rəns/Submit
noun
1.
the action of mentioning or alluding to something.
"he made reference to the enormous power of the mass media"
synonyms: mention of, allusion to, comment on, remark about
"his journal contains many references to railroads"
2.
use of a source of information in order to ascertain something.
"popular works of reference"
verb
1.
provide (a book or article) with citations of authorities.
"each chapter is referenced, citing literature up to 1990"
TheGhostofOtto1923
not rated yet Oct 17, 2017
Developing a suitable arrangement of fields that contain the fuel ions without introducing turbulence or leaking the fuel at a profuse rate has proven to be a difficult problem."
Right. And so where does it say that
the result is particle and heat leakage as the particles now have another magnetic "route" they can follow
-? Ions leak, contact the vessel walls, and cool the plasma. They don't 'follow' anything.

What specifically makes you think that ions are following some alternate "magnetic "route"?

That's what you need to search all of 'particle physics' for.
TheGhostofOtto1923
not rated yet Oct 17, 2017
Leak - "a hole in a container or covering through which contents, especially liquid or gas, may accidentally pass..." Ya see, in magnetic containment the only "leak" in the field can be another magnetic channel. Since the field configuration doesn't initially have a leak....the only way to create one is an impinging field
Uh no youre making that up. Try momentum and inertia. I'm sure they're in your particle physics book.
So now you are part of EU....could mean a ratings dive
Otto has more posts here than anybody. But go ahead - knock yourself out.
gculpex
5 / 5 (1) Oct 17, 2017
TheGhostofOtto1923
not rated yet Oct 17, 2017
https://phys.org/news/2017-10-plasma-optic-combines-lasers-superbeam.html
haha yeah really. How apropos. Modgods really do read what we write.

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