reddit: We are nuclear fusion researchers, ask us anything

[ladajo]

Do you know what POPS is?

Yes, I do: Periodically Oscillated Plasma Sphere.

Are you aware of Nebel and Park's history with POPS?

[Joseph Chikva]

Do you know what POPS is?

Yes, I do: Periodically Oscillated Plasma Sphere.

Are you aware of Nebel and Park's history with POPS?

Is that so important or more important how POPS does work?

[ladajo]

Both.

[ladajo]

And of course that two senior, well seasoned, very experienced, excellent reputation and multiply published Plasma Physics Scientists could be wrong about seeing Beta=1 in machines they have helped build and operate to do exactly that.

Are you ever going to bother to learn about what you wisk to critque? Or should we just stop paying attention to you now?

Fusors are not Tokamaks.

[Joseph Chikva]

And of course that two senior, well seasoned, very experienced, excellent reputation and multiply published Plasma Physics Scientists could be wrong about seeing Beta=1 in machines they have helped build and operate to do exactly that.

If two senior, well seasoned, very experienced, excellent reputation and multiply published Plasma Physics Scientists consider particle losses as overcoming of beta=1? It is interesting for me how they measured beta? Is this published anywhere? May be they simply defend their bowl of rice as one of participants here said about people of MIT? Very poor bowl by the way. Everyone has weakness.

Or should we just stop paying attention to you now?

That's your right.

[ladajo]

I do not see them defending anything. If anything, they maintain that it may not work. Hardly a strong defense.

What are you defending?

[Joseph Chikva]

What are you defending?

Nothing. Just thoughts aloud.

[D Tibbets]

P fusion ∝ β^2 B^4 R^3 (5)

This product if admitting that β is not constant daramaticaly differs from considering here product B^4 R^3.
As in any device β is a function of many parameters and varies from 0 to 1.
And when β=0 Pfusion=0 too.
For your reference poloidal β in TOKAMAK is rather high while toroidal field is applied there for improving stability.

And here I see the groundless statements of people about absolute plasma stability in the device as though they have as confinement object not plasma but solid state.
I would believe to those people including for example Dr. Nebel if they would say that as result of theoretical and experimental investigations the certain stability area has been found. And in that area β value from 0.6 to 0.8 can be achieved. As this and this types of instabilities can be damped with the help of this and this ways. And they (instabilities) have acceptable scale. But such an unconditional statement that a beta is equally to 1 in all range of operating conditions is lightly and very unworthy. As turbulence and instabilities even if they have not catastrophic scale are in existence in any plasma device.

Once I wrote here such an analogy.
Let's imagine swimming pool filled to the edges with absolutely quiet water. This is a plasma device with a beta equally to 1.
As soon as there in this pool will appear waves, water will start to overflow and volume taken by water in a quiet condition excluding the water overflow will be less than pool’s volume. And will be dependent on intensity of waves. And only that will be a real β value.

Joe, when you aregue that Beta can vary, that is certainly possible in select situations. But consider that Beta can also be constant. It doesn't matter where it is constant at ~ 0.1 Beta or ~1 Beta, so long as it is constant. The equation then simplifies from Beta^2 *B^4 *r^3 to Constant * B^4 * r^3. For scaling changes the constant can be ignored and the equation becomes B^4 *r^3.

The quiet water in a swimming pool that then becomes agitated and sloshes over the edge is indeed a good analogy. This macro instability is inherent in a tokamak. Whether you accept it or not, the claim for the Polywell is that it is stable, there is no sloshing of the water. How many times have you seen mention that the magnetic field lines in a Polywell are ALWAYS convex towards the center of the plasma (at least till the cusps are passed). This is a key feature of the design. You can argue stability from MHD standpoints, but you have to concede that these MHD principles that serve to describe behavior in a tokamak are not applicable, or at least much modified, when talking about a Polywell.

In a later post, when you mention the Troyon Limit, you are again using a tokamak specific term concerning MHD considerations.
http://plasmadictionary.llnl.gov/terms. ... age=detail
The Polywell is a completely different situation which you ignore. Some tokamak specific features might apply to Stellorators or FRC or Polywells, others may not. You have to understand the physics of each. Applying features of one to another is very dangerous unless you are very careful.

You keep spewing tokamak theory and understanding, while ignoring that a Polywell is fundamentally different in many ways.
Try this analogy. A tokamak is a rocket. It has to carry (contain) both the fuel and the oxidizer (electrons and ions). The Polywell is a jet engine. It has to carry the electrons, but the ions are almost free (from a containment perspective). They both work by burning and ejecting hot gasses, but the internal dynamics are very different.

Some of the differences:
1)Magnetic fields stable- no swimming pool sloshing
2)Magnetic containment of ions is trivial .
3)Electrostatic containment of ions is dominate. This is absent in tokamaks. There may be some electrostatic ion containment in the Tri Alpha approach to the FRC.
4)Confinement of electrons and ions is tremendously worse than in large tokamaks, but this is more than made up for by density advantages.
5) Thermalization issues are much different and there are restoring mechanisms- annealing, selective removal of up scattered ions.
6) Electrostatic acceleration of the ions allows for much higher temperatures making fusion of D-D and aneutronic fuels more feasible
7) thermodynamic features of the electrons may allow for overcoming the other impediment to profitable aneutronic fusion- bremstruhlung losses
8 ) No ignition. The cusps allow for natural escape of fusion ions with little heating of the fuel plasma
9) other differences...

These are real claimed differences.You can argue the validity of these differences, but you cannot ignore them and apply tokamak understanding blindly.


Dan Tibbets

[Joseph Chikva]

Joe, when you aregue that Beta can vary, that is certainly possible in select situations. But consider that Beta can also be constant.

I can not. Thanks.

[D Tibbets]

Joe, when you aregue that Beta can vary, that is certainly possible in select situations. But consider that Beta can also be constant.

I can not. Thanks.

Why? You have argued that B^4 r^3 power scaling is completely wrong. Yet you seem to accept Beta^2 B^4 r^3 scaling. A simple algebraic manipulation shows that both formulas are the same with an assumption. You must accept the scaling law. Granted you can assume any Beta you like, and you can assume any rate of change you like. But unless you assert that the rate of change of Beta is much faster than any other plasma parameter you have to admit relative stable beta on some significant time scale. And, even if you don't you have to admit that time averaged values will approximate a stable beta. And, all of this is without admitting any Polywell difference from an unstable tokamak.

PS: Will you admit that an opposing magnet biconic cusp mirror machine is MHD stable. It's containment of electrons is similar but poorer than the claimed cusp confinement in a Polywell (before any consideration of Wiffleball formation). These machines are considered to be MHD stable . They fail because of the large equatorial line cusp loses, not due to macro instabilities like a tokamak or a solenoidal mirror machine.

[Joseph Chikva]

Joe, when you aregue that Beta can vary, that is certainly possible in select situations. But consider that Beta can also be constant.

I can not. Thanks.

Why? You have argued that B^4 r^3 power scaling is completely wrong.

Because β^2 B^4 R^3 is correct and if to consider that β is dramatically decreasing function of many parameters, this mathematically differs totally from B^4 R^3 "If to admit that β is constant" brings a big confusion from the beginning.

[D Tibbets]

Claims that Beta=1 is an absolute maximum may not be the true. At least in some cases such a this one, much higher Betas may be possible :
https://e-reports-ext.llnl.gov/pdf/240983.pdf
page 79

Dan Tibbets

[Joseph Chikva]

Claims that Beta=1 is an absolute maximum may not be the true. At least in some cases such a this one, much higher Betas may be possible :
https://e-reports-ext.llnl.gov/pdf/240983.pdf
page 79

Dan Tibbets

Are you talking about "Application of the Penning trap to the study of Penning trap to the study of neoclassical transport"? I do not see there any mention of beta.

Pardon I've read page 77 for the beginning.
I do not understand well what "Magnetized Target Fusion" is.
Think that inertial confinement there is more significant than magnetic. As there are approches e.g. Laser Driven Confinement, Heavy Ions Fusion that do not use magnetic field confinement at all. "Magnetized Target" may have and may not advantage vs. non-magnetized. How correct in that case is to talk about beta?
I do not know.

I've just read:

In general terms, MTF is an inertial method.

Magnetic fusion confines a dilute plasma at about 10^14 cm^−3. Inertial fusion works around 10^25 cm^−3. MTF aims for 10^19 cm^−3.[1]

So, there main confinement is made by inetial forces and not magnetic. Magnetic fields needed for confinement of 10^19 cm^-3 would be unrealizable high. As 10^19 cm^-3 = 10^25 m^-3.

[KitemanSA]

TOKAMAK having concave field always showed better confinement against Stellarators having convex field. As poloidal field in TOKAMAK decreases by increasing of radial coordinate, while in Stellarators all happens oppositely.

Sorry, I know a little about the stellarator. As described in wikipedia, it has the same concave fields that the tok does but tried to solve the drift problem differently (and less successfully as it has turned out SO FAR).

Convex field had all mirror kind of machines. All them are forgotten now.

If the Polywell were trying to confine the plasma with magnetic fields, it would be forgotten now too. But that is the GENIUS of the Polywell. It is confining the plasma with an electrodynamic well, not a magnetic field. ED wells are quite stable against minor perturbations.

Studying only Polywell history may be better if you get studied also what has been done in fusion research during past 60 years.

I have looked the general history a bit, enough to understand the failings of most of the big money machines to date. Polywell doesn't have those failings. It may have OTHERS, but not those.

By the way, what do YOU mean by concave and convex fields? Just asking to be sure we are talking the same language.

[Joseph Chikva]

TOKAMAK having concave field always showed better confinement against Stellarators having convex field. As poloidal field in TOKAMAK decreases by increasing of radial coordinate, while in Stellarators all happens oppositely.

Sorry, I know a little about the stellarator. As described in wikipedia, it has the same concave fields that the tok does but tried to solve the drift problem differently (and less successfully as it has turned out SO FAR).

Convex field had all mirror kind of machines. All them are forgotten now.

If the Polywell were trying to confine the plasma with magnetic fields, it would be forgotten now too. But that is the GENIUS of the Polywell. It is confining the plasma with an electrodynamic well, not a magnetic field. ED wells are quite stable against minor perturbations.

Studying only Polywell history may be better if you get studied also what has been done in fusion research during past 60 years.

I have looked the general history a bit, enough to understand the failings of most of the big money machines to date. Polywell doesn't have those failings. It may have OTHERS, but not those.

By the way, what do YOU mean by concave and convex fields? Just asking to be sure we are talking the same language.

Concave is concave and convex is convex. Please quote where is written that stellarators have the same concave field. As if to follow minor radius poloidal field in TOKAMAK decreases from the edge of plasma torus and to infiniteness, while for Stellarator increases.
And the main idea is in that plasma having diamagnetic properties should aspire in the space with the lowest B field. And we can see the same principle when draw convex power lines in magnetic traps (mirror machines).
Big money or small budget program - it does not matter. We are talking about world challenge. And price of energy will grow in long-term prospect in process of fossil fuel exhaustion. So, let's give even expensive but viable concept.