Let us start discrediting tokamak fusion. Wrong Shape.

Discuss ways to make polywell research more widely known or better understood. Includes education and outreach.

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jmc
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Postby jmc » Thu Feb 28, 2008 10:54 am

When tokamaks were built, they performed worse than anticipated by theory but better than other devices. I was talking more in terms of the 50's then the 60's and 70's. I'm not quite sure whether some people hoped their performance could be improved through innovation an dampening out the turbulence eventually.

jmc
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Postby jmc » Thu Feb 28, 2008 11:24 am

MSimon wrote:
jmc wrote:What if we abandon the tokamak programme for Polywells instead? What if we find all sorts of unanticipated problems and it takes forty years to build a Polywell that produces net power? At this point we might decide we suddenly have to do all sorts of work on materials that can withstand high plasma heat fluxes as well as neutron bombardment (assuming the Polywell is DT). At this point we'd have wished we had kept the tokamak programme going so that all the materials work had already been done.

While I don't agree with tokamaks strangling all other fusion programmes in terms of funding, I do believe that they should be continued until another kind of fusion can overtake them in measured performance.

If we find out lots of unanticipated problems in BFRs, we can solve them on a small budget - say we have to build a new type WB-100 every year. That will run us $200 mil a year (assuming rush jobs and small auxiliary test reactors).

To do a new ITER every year is not even possible - let alone doing it on a budget of less than $20 bn a year.

Plasmas self organize. Do we want to build reactors that are based on enhancing that natural self organizing tendency? Or do we want to build reactors that depend on opposing that natural tendency?

As to roll out: I can imagine a program that could deliver a working reactor to a Navy ship in 4 years. If we don't mind the waste of stopping a high velocity program if we hit a serious snag.

One way to cut the time required is to run the program on a 24/7 basis. Another way is to build lots of vacuum chambers so experiments can go on while new set ups are being fitted to one of the idle chambers.

I could see a BFR industry producing 1,000 100 MW jobs a year within 7 years of the announcement of WB-7 results - if further efforts are warranted and the money is there.


Who says we can solve them on a small budget? Maybe we can, maybe we can't. The current BFR's built (albeit with very little funding) have not shown evidence of annealing, the HEPS was a disaster and the latest machine which produced 10^9 neutrons has only got 9 counts to support it over 5 shots. And even if it is correct its still a factor of a trillion behind tokamaks (although its good for IEC in a 10Kev well).

200 million a year for twenty years is 4 billion. That's comparable to the ITER programme.

Yes plasmas do self-organize, but they tend to self organize themselves towards the walls of the vessel. One good thing abouth the BFR is the convex fields. A bad thing about the BFR is the cusps which lead out plasma directly from the core, this is a disadvantage compared with Tokamaks, well blowout is also a big challenge when you try to push the density up and a stable wiffle ball has never been achieved to date. The Polywell would be a superhigh beta device, which could make it incredibly economical if it works. But super high beta devices has big problems with selforganisation, which makes it very hard to tell how the plasma will behave. Conversely low beta devices with high magnetic fields tend to be more stable (and less economical.)

If the Polywell plasma self organizes itself the right way, then we're certainly on to a winner, but there no conclusive experimental evidence of this. When there is and a polywell is built hat spews out neutrons, only then will I be prepared to criticise the tokamak programme as a waste of money.

With regard to the Polywell navy ship in 4 years: unlikely in the extreme, the physics hasn't been proven by experiment the devices built to date are miles away from being a working reactor why should it be possible to get it to work in four years.


The difference between tokamaks and Polywells is that we know Tokamaks can be made to work, but we also know its going to take a long time and a large machine. This eliminates the possibility of wishful thinking.

In the case of Polywells, we know so little about them and the experiments done to date were so poorly diagnosed that you can literally fantasize about any kind of physics inside them that you want, and know one can conclusively prove you wrong. The devices to date are also so small, and the scale of problems of getting them to working as a net power producing reactor are so unknown that its also possible to fantasize about how they'll all turn out to be trivial and how it'll work fine in 5 years or whatever.

Maybe Polywells can be made to work, I'd like to see them work, I'd even like to wok on the Programme myself. But there's a good chance the path towards fusion power may well be just as gruelling and slow along the Polywell route as it is for Tokamaks, (although the final device may be more economical.)

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Postby MSimon » Thu Feb 28, 2008 3:44 pm

jmc,

I think 7 years is doable if the physics is even close.

As to that question - the experimenters say it is close. If they are correct it is my engineering judgment that a program can be designed to produce a working reactor in three years according to program design - four years actual time.

In fact I could see producing a working reactor in two years - although the chances are slim.

BTW annealing has been seen in other plasma contexts so the phenomenon is not unknown.

I don't see any real long shots re: physics.

In fact the more I have looked into Dr. B's work the more mainstream I have found it.
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jmc
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Postby jmc » Thu Feb 28, 2008 5:34 pm

His work is mainstream in the sense that it involves hot ions colliding with each other at high energy. Its perfectly physically plausible in that sense.

On the annealing front, are you referring to synchronisation in the Zafman Trap? I read something about that in Thomas McGuire's thesis, it was very low density. One of the criteria that was required for synchronisation there was that the period of an ion increases as as the kinetic energy increases, if you start pushing up the density in a polywell the shape of the well is going to look more and more square due to debye screening. In a square well the opposite occurs, the period of oscillation actually decreases as the kinetic energy increases. As far as I'm aware there is no experimental evidence for annealing in a high density plasma device. If you know of any other papers giving experimental evidence for annealing I'd be interested to see them.

As for the experimenters, one or two say its close, Rider and Nevins say its impossible and some others think it may take a long time. In that report featuring Nebel for example, he seemed quite conservative with regards to the polywells potential as a fusion powerplant.

Annealing is a longshot, there's a possibility that those funny cusps might blow open once the plasma pressure is increased, getting losses from the line cusps down might also be a challenge. Getting the equipotential surfaces perfectly spherical is going to be hard, even a slight spherical asymmetry could destroy convergence.

I think it isn't close, the densities and neutron outputs are still far too low to carry out a meaningful extrapolation. A thousand things that haven't been tested can still go wrong. Bussard was elated by WB6 because it just about barely might have worked in producing neutron counts above that of other IEC devices, its still not remotely in the realms of tokamak performance (although it might surpass them someday).

It remains an interesting concept which could eventually lead to a reactor that is far more economic than a tokamak. Maybe the problems could be smoothed out relatively quickly, maybe they couldn't, there simply isn't enough information or experimental evidence to make a meaningful judgement.

In the case where there is no overwhelming evidence either way with regards to how long it will take to get working, the proper thing to do is make an estimate in the context of similar plasma devices, and if we do that we will find it will probably take a very long time. Fusion has a history of new ideas cropping up, people being elated thinking they might just work, running the experiment, complications appearing, thinking of a way around those complications, more complications appearing, and what result is a long slog. That doesn't mean its not worth it for the end result though.

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Postby scareduck » Thu Feb 28, 2008 6:15 pm

jmc wrote:Bussard was elated by WB6 because it just about barely might have worked in producing neutron counts above that of other IEC devices

Relative to the drive of other Hirsch-Farnsworth and Elmore-Tuck-Watson devices, yes, it did outstrip those devices.

Line cusps can be eliminated or at the very least radically reduced by the correct magnet geometry (truncated cube rather than a normal cube, or a truncated dodecahedron).

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Postby MSimon » Thu Feb 28, 2008 8:29 pm

On the annealing front, are you referring to synchronisation in the Zafman Trap? I read something about that in Thomas McGuire's thesis, it was very low density.


No. I'm referring to re-normalization caused by energy interchange in the "low energy" areas of the reaction volume.

I saw a paper on this in the last week or two. I'll see if I can dig it up. It seemed like the paper described a well known phenomenon.
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Postby TallDave » Fri Feb 29, 2008 2:33 am

Who says we can solve them on a small budget? Maybe we can, maybe we can't.


Well, we know we can build them for $200M -- we know, roughly, the prices of the components of the design. What we don't know is if they'll work.

Annealing is a longshot,


But beam bunching is a reality, and I think that was proposed as another solution.

f the Polywell plasma self organizes itself the right way, then we're certainly on to a winner, but there no conclusive experimental evidence of this.


In fact there is, at least to some extent. We know from that Japanese study that IEC devices form a double well, something that had been disputed.

I saw a paper on this in the last week or two. I'll see if I can dig it up. It seemed like the paper described a well known phenomenon.


I'd be very interested to see that. I haven't seen any support for that yet, other than Bussard's claim.

. Bussard was elated by WB6 because it just about barely might have worked in producing neutron counts above that of other IEC devices, its still not remotely in the realms of tokamak performance (although it might surpass them someday).


Well sure, but he was working with a much smaller budget/machine. And since electrons are easier to confine, it's reasonable to expect it will scale better.


It remains an interesting concept which could eventually lead to a reactor that is far more economic than a tokamak. Maybe the problems could be smoothed out relatively quickly, maybe they couldn't, there simply isn't enough information or experimental evidence to make a meaningful judgement.


Yah. But we could say the same for tokamaks, so why not fund Polywell for an order of magnitude less?

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Postby TallDave » Fri Feb 29, 2008 2:46 am

Heh, the Japanese are pretty adamant about it:

Research issues to be resolved
For further drastic improvement of the
fusion reaction rate, however, it is essential
to clarify the mechanism of potential well
formation (see Fig. 5) predicted to develop
in the central plasma core within the
cathode, since potential well formation due
to space charge associated with spherically
converging ion beams plays a key and
essential role in the beam-beam colliding
fusion, i.e., the major mechanism of the
IECF devices. Actually, this has been the
central key issue for IECF researchers for
the past 30 years,
until the first successful
direct measurement of the double-well
potential profile in the IECF device through
the laser- induced fluorescence (LIF)
method at Kyoto University [6] in 1999
with an approximately 200 V dip at the
center in the helium plasma core as will be
described below.


http://wwwsoc.nii.ac.jp/aesj/division/f ... hikawa.pdf

Maybe they're overstating it, but doesn't this prove Rider wrong? If they form a double well, doesn't that mean they don't collapse to thermal equilibrium?

jmc
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Postby jmc » Fri Feb 29, 2008 10:10 am

MSimon wrote:I saw a paper on this in the last week or two. I'll see if I can dig it up. It seemed like the paper described a well known phenomenon.


I'd be really interested to see that.

jmc
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Postby jmc » Fri Feb 29, 2008 10:26 am

TallDave wrote:
Who says we can solve them on a small budget? Maybe we can, maybe we can't.




1)In fact there is, at least to some extent. We know from that Japanese study that IEC devices form a double well, something that had been disputed.

. Bussard was elated by WB6 because it just about barely might have worked in producing neutron counts above that of other IEC devices, its still not remotely in the realms of tokamak performance (although it might surpass them someday).


2)Well sure, but he was working with a much smaller budget/machine. And since electrons are easier to confine, it's reasonable to expect it will scale better.


It remains an interesting concept which could eventually lead to a reactor that is far more economic than a tokamak. Maybe the problems could be smoothed out relatively quickly, maybe they couldn't, there simply isn't enough information or experimental evidence to make a meaningful judgement.


3)Yah. But we could say the same for tokamaks, so why not fund Polywell for an order of magnitude less?



1) Were not home free yet. In a polywell unlike a grid machine there are magnetic fields which might drastically destroy convergence, remember, its only quasispherical, and tiny spherical assymmetries are all that would be required to ruin convergence (unless you pumpup the density)

2) On the issue of scaling better. We done have enough Polywell machine over the required range of sizes to derive any empirical scaling laws at all. The only open box models that produce any neutrons were WB4 and WB6, WB4 had great big whopping corners. The scaling laws came straight out of Bussards head using hand wavy physical assertions, maybe their right maybe their wrong. Either way, you can't be certain that Polywells won't endup being considerably bigger and considerably more expensive than was originally claimed.

3)We certainly should fund a Polywell for an order of magnitude less than a tokamak, but as well as not instead of funding tokamaks. We can do both at the same time. Keep in mind, a Polywell maybe an order of magnitude cheaper than a tokamak, but its several orders of magnitude less likely to work. When real Polywells actual do perform as well as tokamaks then I'll talk about actually diverting tokamak funding, but not before hand.

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Postby jmc » Fri Feb 29, 2008 10:36 am

TallDave wrote:Maybe they're overstating it, but doesn't this prove Rider wrong? If they form a double well, doesn't that mean they don't collapse to thermal equilibrium?


It only proves Rider wrong if they attained breakeven. The crux of the issue of maxwellization is that in order to get fusion, particles have to collide, in order to maxwellize particles have to collide. Thus both maxwellization and fusion depend on density in the same way and the ion-ion collision time is about 1000 times shorter than the fusion collision time at maximum crossection, (although a given fusion reaction may produce about 1000 times more energy than the background plasma temperature)

Having said that if you have a q=0.01 reactor where the ions are lost to the grid or some such its perfectly possible to have a non-maxwellian plasma.

I believe what this paper discusses is the achievement of a poissor potential formation, (a virtual cathode inside the virtual anode ), this does indeed boost the reaction rate and gain, but so long as the net gain (q) remains well below 1 you can still have a non-maxwellian distribution even if Rider is right.

jmc
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Postby jmc » Fri Feb 29, 2008 10:44 am

scareduck wrote:
jmc wrote:Bussard was elated by WB6 because it just about barely might have worked in producing neutron counts above that of other IEC devices

Relative to the drive of other Hirsch-Farnsworth and Elmore-Tuck-Watson devices, yes, it did outstrip those devices.

Line cusps can be eliminated or at the very least radically reduced by the correct magnet geometry (truncated cube rather than a normal cube, or a truncated dodecahedron).


Line cusps can indeed be eliminated at the expense of 'funny cusp' corridors of zero magnetic field that lead straight to the corners. The effective hole size for electrons at funny cusps at zero particle pressure, I believe, is not very high, due to the small larmor radius of the electrons. The field surrounding these funny cusps is very low however, and I would suspect as the pressure is increased the electrons (and maybe even the ions) might push back the field causing the corridors of zero field that allow the electrons to escape to become much wider.

These funny cusps exist at the corners of the ideal truncated cude (or any other concievable polywell) geometry.

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Postby TallDave » Fri Feb 29, 2008 4:56 pm

It only proves Rider wrong if they attained breakeven.


Yah, that's true. The higher energies/densities could break the well, which now that I look at it was Rider's point in his thesis. Still, somewhat encouraging.

When real Polywells actual do perform as well as tokamaks


Well, it's not really a fair comparison. Tokamaks have received funding a couple orders of magnitude higher than IEC. Could Polyell have been achieved the same results with that level of funding? That's probably a fairer question.

jmc
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Postby jmc » Sat Mar 01, 2008 1:54 pm

Yes but even Tokamaks started out at a low level low-budget program. Originally infact nobody thought they'd work as well as stellerators. The tokamak programme only ballooned in size once the outstripped the other machines in meassured performance.

Like I said before we should investigate all the different fusion approaches, but I certainly wouldn't advocate abandoning a high performing fusion machine until something that meassurably performed better was found.

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NIF will change perspectives.

Postby Helius » Sat Mar 01, 2008 11:51 pm

jmc wrote:.....we should investigate all the different fusion approaches, but I certainly wouldn't advocate abandoning a high performing fusion machine until something that meassurably performed better was found.


The abandonment of other approaches should always be avoided. The highest performers should get the lion's share of the available money, but much may be gained by concurrent alternative approaches. I fear for the Tokamakers, once NIF comes on line and exceeds the metrics of all other approaches, including ITER. NIF experiments will follow so quick, that they will certainly pin down parameters for high Q and, eventually quick repeatability. IEC - polywell and Tokamaks will both be under budgetary threat. I predict good budget flows to the University of Rochester for their inertial confinement research, and also the Hiper project if NIF is as successful as it now seems it will be. Woe be to ITER, woe be to Polywell if the prespective is that only the single most promising approach gets *all* the money.


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