reddit: We are nuclear fusion researchers, ask us anything

[Skipjack]

Joseph, again I am saying economic fusion reactor. That means that the cost of building one and operation of one is low enough to make a sufficient amount of profit compared to other energy generation methods.
With Tokamaks this does not seem to be the case and definitely NOT within the next 10 years. Can we aggree on that?
Now with the other concepts it is possible if they work as adverticed. I am not saying they will, but there is at least a possibility. With Tokamaks the possibility is ZERO.

[KitemanSA]

You need the source that B^4 does not work? This scaling law would be quite universal if that works. But we have about 60 years of fusion research history.

Did they keep all else equal? No? Well then, the scaling law of B^4 "with all else equal" wasn't applied. You seem convinced that confinement schemes that failed with tokamaks and ion mirrors and ion cusp containment... will NECESSARILY result in the same failures with electron confinement in a MaGrid. Different design, different result.

And for any device that does not work. That is fact. In opposite case we would have an "economic reactor" right now.

Since almost all the the other "fusion" devices try to confine ions, they may never get to a practical condition. It is a lucky thing that Polywell only confines electrons magnetically.

Beta goes to 2? Thanks. Funny.

Almost as funny as your statement that 1x2 = 1/2.

I can read technical English. There is the talk about electron-electron 2-stream instability. As initially only electron population in Polywell has large angular momentums.

I have asked you several times to show me ANY documentation that says the angular momenta are "large". You have failed REPEATEDLY to do so. Put up, or shut up, please.

And not ions. Read it carefully. This is important. Increasing density by pumping more ions and electrons and strengthening mag field in space confined by cusps you will get another plasma properties. And ion-electron 2-stream was not investigated.
Or till now you still mean that this type of instability is not an issue for Polywell?

Dr. N. says two stream instability is not an issue. He has worked with it, you haven't. Until I get direct first hand knowledge, I will take HIS word over yours.

At least "eminent fusion physicists" at MIT are better trained in plasma physics than you, me and any other visitor of this board. It is a pity for me that they remained jobless.

So send them your money. Personally, I'm not unhappy they are jobless.

I think that they give you realistic estimation of cost of TOKAMAK program. For example Heavy Ions Fusion program would be even more expensive. But recall that cost of program is not equal to cost of hardware.

And if the size and cost of ITER hardware is any indication, toks will never be cost effective, even if there is no paying back the G$ of research money.

But I feel that you and many others here hope to solve one of world's main challenges at e.g. vacuum cleaner's development cost.

It would be nice, but I suspect it would cost ~0.2 G$

I remember how you estimate nickel enrichment hardware's cost (couple thousands dollars). Good luck.

Thanks, but at the moment I am not really interested in enriching Ni. But it is nice to know how to do it cheaply if I ever need to.

[hanelyp]

B^4*R^3 derives from straight forward physics.

Magnetic pressure is proportionate to B^2.
Fusion rate is proportionate to density^2.
-> fusion rate proportional to B^4.

R^3 is simply the volume of the fusion plasma.

I's also posit a beta^2 term from the relation between plasma and magnetic pressure, giving B^4*R^3*beta^2. Beta, along with several other subtle factors, are functions of the reactor design.

Where scaling has not worked as expected on the tokomak is loss scaling, the rate at which energy escapes the plasma for different reactor sizes. This is also an area of some uncertainty for the polywell, at least for us without experimental data.

As far as fusion products being confined by the magrid field, they are not expected to be contained long enough to transfer much energy to the plasma before escaping through a cusp. Keep in mind that between high energy and mass much higher than electrons, the cusps holes are much larger for fusion ions than electrons.

[Joseph Chikva]

Did they keep all else equal?

"All else equal" happens only on Egyptian Pharaohs' cemeteries.

"Dr. Nebel said that is not issue". Three differnt ways for avoiding of 2-stream is possible:
1. Broad spread of velocities in the streams
2. Axial magnetic field expands stability area
3. High relativistic factor for at least one of streams.
Which one is possible for ion-electron 2-stream instability in Polywell?
As I am repeating once again: intially ions in Polywell are not thermal, while electrons are.

Good luck.

[D Tibbets]

Electrons are not thermal in a Polywell, and never can be so long as there is a threshold where up scattered electrons are not recirculated by the positive charge on the magrid. Bussard has stressed that the loss of these up scattered high energy electrons is very important and desirable so long as the overall electron losses are tolerable.

Also, if it has not been mentioned recently, the near spherical geometry has a major role. So long as more than a trivial amount of electrons collide near the center the angular momentum change will be reduced.

I'm not sure how much of this is significant anyway. It is generally conceded that the electrons alone quickly assume a population with the highest density near the Wiffleball border- i.e: a large amount of angular momentum. This produces a square shaped potential well. The ions introduced outside of this shell quickly accelerate, but once past this shell their continued inward motion is all inertia. This is a static view, but once the ions pass the shell of electrons they tug the electrons along to a degree, because of the difference of momentum/ inertia between the ions and electrons. This local effect dominating over space charge effect (some coupling) applies to the electrons, but to a much smaller extent to the ions due to the momentum differences and time constraints. This changes the shape of the potential well and with other considerations can lead to even more complex potential well shapes and provides for complex charged particle distributions and local velocities.

PS: The ions would also tend to tug the electrons outward while they are at the top of their potential well. Two important considerations in this is that the electrons are contained magnetically, so their outward excursion is dampened except when a cusp is hit and this occurs only ~ 1/10,000 orbits. The other consideration is the excess electrons that produce the space charge which is what is confining the ions. With momentum consideration any local pairing (coupling) is quickly overwhelmed from the ions perspective. That is my understanding of why the ions do not follow the electrons out of the cusps - unless the cusps are compromised in other ways, like the electron repellers in WB5. I understand this produces concentrations of cold electrons in the cusps and these local collections overwhelm the central negative space charge to a degree and allows the weak coupling to tug the ions outward to catastrophic radii.


Dan Tibbets

[Joseph Chikva]

Electrons are not thermal in a Polywell,...

Is there motion random? One pass till following scattering event or till following deflection from the casp. If so, this is thermal, Dan.

[KitemanSA]

B^4*R^3 derives from straight forward physics.

Magnetic pressure is proportionate to B^2.
Fusion rate is proportionate to density^2.
-> fusion rate proportional to B^4.

R^3 is simply the volume of the fusion plasma.

I posit yet again a language barrier. You and I talk about "power" scaling at "B^4R^3, all else equal" and he hears "gain". Then he argues about how the "power" does not scale that way. Look back and you will find that all his "examples" relate to gain, not power.

Joe,
The POWER output of any mag fusion device scales as B^4R^3, all else being equal.
The LOSSES of any fusion device scale weirdly and wondersously and are the primary subject of the "scaling" research in Polywell (and ITER for that matter). Dr. B. predicted loss scaling near R^2.25 for Polywell, all else being equal.
The GAIN is POWER - LOSSES. Once you get into the positive gain side, the GAIN would scale ~R^5, all else being equal.

[KitemanSA]

Electrons are not thermal in a Polywell,...

Is there motion random? One pass till following scattering event or till following deflection from the casp. If so, this is thermal, Dan.

Random direction, mono-energetic is NOT thermal.
Dr. B. wanted to research Polywells with better sphericity before going to the demo scale unit. This suggests he thought that better redirection toward the center from all sides would be a benefit. This would suggest a less random direction but still mono-energetic.

[KitemanSA]

Did they keep all else equal?

"All else equal" happens only on Egyptian Pharaohs' cemeteries.

I've never seen ANY pharaoh's tomb be equal to any others, so this is a ridiculous analogy.

When researching into "scaling" one tries very hard to minimize variability of factors not being researched. On keeps "all else equal" as best one can. And when one keeps "all else equal" the POWER scaling equation stated many times above holds.

"Dr. Nebel said that is not issue". Three differnt ways for avoiding of 2-stream is possible:
1. Broad spread of velocities in the streams
2. Axial magnetic field expands stability area
3. High relativistic factor for at least one of streams.
Which one is possible for ion-electron 2-stream instability in Polywell?
As I am repeating once again: intially ions in Polywell are not thermal, while electrons are.

Once again you miss one. One way to not have two stream instability is to NOT have "STREAMS". No streams, no instability.
Even if you start with streams and they intersect near the center and become "not streams" (gain a broad spread of velocities) the velocities will be predominantly radial, there is no other direction for them to go.

[Joseph Chikva]

Kiteman, reread three you above posts and see that in one of which you said "random direction but monoenergetic", in the second " gain broad spread of velicities". It is interesting for me does "broad spread" mean "monoenergetic"?
Regarding B^4*R^3, gain or power is proportional to n1 *n2<vσ> . That's true. But ni is not proportional to B^2. As condition "all else are equal" never kept. May be I am truly an idiot if I am explaining you the things which you should comprehend yourself.

[ladajo]

Kiteman, reread three you above posts and see that in one of which you said "random direction but monoenergetic", in the second " gain broad spread of velicities". It is interesting for me does "broad spread" mean "monoenergetic"?

No it does not. It means exactly the opposite. Why would you think it is the same meaning? Language barrier?

Regarding B^4*R^3, gain or power is proportional to n1 *n2<vσ> . That's true. But ni is not proportional to B^2. As condition "all else are equal" never kept. May be I am truly an idiot if I am explaining you the things which you should comprehend yourself.

Joseph,
You alone of most of the analysts think that the rule does not apply. Can you find someone reputable that agrees with you that B^4*R^3 is wrong? Do you not also understand that this does not take account for losses? That is a seperate term in the gain function?
Do you not understand that the central point is scaling gain increases faster than scaling of losses, and the entire point of the research to see if not the gain equation but the loss estimatation is accurate? Everyone accepts the generic gain solution except you...it is the losses that are in question. Even your oft quoted Ryder accepts the gain function. He argues the losses...
Why do you not see this? Why are you the lone world renoun plasma physics expert that disagrees?

I still think you do not understand the polywell concept. Or at least your ability to communicate your understanding is challenged, as well as your ability to understand what others repeated explain to you using different formats and methodology.

Some say the definition of stupidity is trying the same thing over and over and expecting a different outcome. Maybe we are stupid to try to explain to you where you have misconceptions over and over again.

And, please, for gods sake, cite and argue. Just once, cite and argue. Please? We have done it for you many times. But is becoming more and more apparent that you do not read the citations we have offered over and over as the basis for our arguments.

You make claims of quotes that your never prove. You ignore the information provided by the folks that are actually doing the work. You ignore the analysis, argument and explanations of others that are trying to expand your understanding.

You can have constructive discussions here, or not. It is up to you. I, for one, am of late asking myself a number of times why I continue to bother with you. Maybe I still have a shred of hope you will open your mind, and actually do some of the legwork on your own. A small shred that you will stop living in the shadow of your father, who did his own legwork.

It remains to be seen if polywell will achieve breakeven. If it does not, I posit it will be for none of the reasons you have thus far tried misguidely proffer. But then again, it may well work. And, I suppose, it will be with some caveats that are yet to be understood by us and the researchers.

In any construct, its ability to function/or be proven not is surely at a cost of resources and effort magnitudes less than ITER, which will NEVER be economical to build and operate, EVER. Even the people building it admit that.

I have lost count how many times you have become tedious. You are an intelligent man, but I would also offer, one that is very set in his ways and perceptions. This does not make for a good scientist. You demonstrate repeatedly that you are not willing to learn, unless it is on your terms, and to your preconceived outcome.

[Joseph Chikva]

Kiteman, reread three you above posts and see that in one of which you said "random direction but monoenergetic", in the second " gain broad spread of velicities". It is interesting for me does "broad spread" mean "monoenergetic"?

No it does not. It means exactly the opposite. Why would you think it is the same meaning? Language barrier?

I do not think that it is the same meaning. My opponent made both these statements in his two posts. Not me.

[Joseph Chikva]

Joseph,
You alone of most of the analysts think that the rule does not apply. Can you find someone reputable that agrees with you that B^4*R^3 is wrong?

Kiteman correctly said already when scaling B^4 would work "all else are the same". But at different B all else are not and can not be the same in any plasma device. As changing number density properties change. Increasing mag field 70-100 times in Polywell you will confine some products of reaction thus intensing thermalization. Instabilities are observed in any plasma device. But they may have non-catastrophic or catastrophic aftereffect. And mainly this circumstance limits beta value. So, your confidence in beta=1 is a little bit funny. I need not to seek any reputable man for confirming so simple things. If you do not believe me ask anyone from yourself. You can show this discussion.
Best regards,
Joseph

[ladajo]

Why do you want to have 7-10T B field?

In any event, at the tested levels, the containment of products has not been an issue. And the envisioned Net machine is 1.5 meters at say 2-3T.

This has been discussed several times about the actual costs to build and run for breakeven, a machine based on MRI coils.

I think you are wrong to think that products will be contained in the envisioned machine.

I think you can also change parameters beyond the scope to your hearts content to manufacture possible problems.

Losses are the issue at hand. Not gain. Do you not get that?

[WizWom]

Increasing mag field 70-100 times in Polywell you will confine some products of reaction thus intensing thermalization.

OK, lets take this single point.
You electron injection is ~30keV. Lets play real easy and say we have a full coulomb net charge in the well, and we will pretend it is a point charge (worst case).

mean velocity of an electron (gaussian): 102e6 m/s
mean energy of an Alpha from D-D fusion: 23.8 MeV
mean velocity of an alpha: 33.9e6 m/s

assume the alpha is created in the exact center, and must escape from alcatr, er, the polywell.

a = F/m
F = k*Q1*Q2/x^2
where
k = 8.99e9 Nm2/C2
Q1 = 1 C
Q2 = 3.2e-19 C
m = 6.65e-27 kg

integrate from 0 to 1 m for total acceleration of 4.32e-32 m/s

conclusion: even mega-coulomb well depths will not cause significant deceleration of fusion products.

Now, right at the magnet, you are saying the magnetic force will "confine" the particle (even though magnetic force only prevents contact of the particle with the grid). So let's work out the cyclotron radius at the surface, assuming 5T

r = mv/qB
so r = 0.14 m

but for an electron, at 30keV r = 1.17e-4 m

So, the magnetic field will not prevent the alpha from impacting, its gyro radius is way too large.