And yet we see in simulations that a significant radial component forms. In fusors (no magnetic field) it is visible.Art Carlson wrote:I agree with Chris that an ion velocity distribution with purely radial velocities will be highly unstable. I assume that the distribution will be everywhere nearly isotropic, and not too far from Maxwellian. That contradicts the polywell orthodoxy, but even Rick Nebel doesn't seem to insist very strongly on this point.
Total ion flux in a Polywell - disruption to magnetic field?
Engineering is the art of making what you want from what you can get at a profit.
So the answer is that it is simulations that provide the idea the ions will have purely radial motion.
Does the simulation also include predictions for the shape and strength of the magnetic fields generated by the coils, with all the little defects you would get in symmetry, or does it run with an imposed overlay of magnetic field built into the simulation with a presumption of a perfectly uniform cusp region?
If you could balance a dense liquid on top of a thinner liquid and defy the Rayleigh-Taylor instability then Zeta would have been pumping out fusion-power neutrons in the 1950s. It's the combination of instability and small perturbation/deviation that kills systems like this. Assume mathematical perfection and the simulation may predict 'a system' but it is not one seen in this Universe, only in the dreams of a computational model.
Are there any published works on field instability/small perturbation models run for Polywell?
Does the simulation also include predictions for the shape and strength of the magnetic fields generated by the coils, with all the little defects you would get in symmetry, or does it run with an imposed overlay of magnetic field built into the simulation with a presumption of a perfectly uniform cusp region?
If you could balance a dense liquid on top of a thinner liquid and defy the Rayleigh-Taylor instability then Zeta would have been pumping out fusion-power neutrons in the 1950s. It's the combination of instability and small perturbation/deviation that kills systems like this. Assume mathematical perfection and the simulation may predict 'a system' but it is not one seen in this Universe, only in the dreams of a computational model.
Are there any published works on field instability/small perturbation models run for Polywell?
chris,
I have only seen the simulations. I couldn't tell you about the underlying math.
In fusors "star formation" is considered normal and is the result of reasonably built eqpt.
So although it is "not possible" it happens.
I have only seen the simulations. I couldn't tell you about the underlying math.
In fusors "star formation" is considered normal and is the result of reasonably built eqpt.
So although it is "not possible" it happens.
Engineering is the art of making what you want from what you can get at a profit.
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Art Carlson
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Which simulations are those? Hopefully not the 1-D simulations that only allow radial velocities. Are deviations of the potential surfaces from perfect spheres taken into account? Is enough physics included to produce the two-stream instability in principle? What additional physics prevents it from occurring?MSimon wrote:And yet we see in simulations that a significant radial component forms. In fusors (no magnetic field) it is visible.Art Carlson wrote:I agree with Chris that an ion velocity distribution with purely radial velocities will be highly unstable. I assume that the distribution will be everywhere nearly isotropic, and not too far from Maxwellian. That contradicts the polywell orthodoxy, but even Rick Nebel doesn't seem to insist very strongly on this point.
Anyways, back to the issue of the total ion flux disrupting the core.
If we need a total flux of 20MegaAmps flowing into the core and there is just a 1% variation in the flux coming into one hemisphere of this 1cm core compared with the flux into the other hemisphere, then we'd have a differential current of 100kA across the core.
As a ball-park estimate, with the permeability set as in a vacuum at 1.26E-7 T.m/A, then we'd get 0.01T.m of magnetic moment, or 1T across the core's radius of 1cm. That is, comparable, and therefore disruptive, to the central core's field.
Clearly this is just an order of magnitude estimate, but if the device cannot tolerate just a 1% delta between the 'north-to-south' particle fluxes, which seems reasonable to me, then such instabilities need to be considered with utmost detail.
If it is thought that the flux will be utterly symmetrical, much better than 1%, then let me ask - how will this be fuelled? You have to put fuel into some port of the device and this will be asymmetric unless you put in hundreds of such fuelling ports to try to achieve isotropy.
If we need a total flux of 20MegaAmps flowing into the core and there is just a 1% variation in the flux coming into one hemisphere of this 1cm core compared with the flux into the other hemisphere, then we'd have a differential current of 100kA across the core.
As a ball-park estimate, with the permeability set as in a vacuum at 1.26E-7 T.m/A, then we'd get 0.01T.m of magnetic moment, or 1T across the core's radius of 1cm. That is, comparable, and therefore disruptive, to the central core's field.
Clearly this is just an order of magnitude estimate, but if the device cannot tolerate just a 1% delta between the 'north-to-south' particle fluxes, which seems reasonable to me, then such instabilities need to be considered with utmost detail.
If it is thought that the flux will be utterly symmetrical, much better than 1%, then let me ask - how will this be fuelled? You have to put fuel into some port of the device and this will be asymmetric unless you put in hundreds of such fuelling ports to try to achieve isotropy.
chris,
And yet if you look at the plasma pictures available from EMC2 it appears that star formation happens there too. Of course we do not have enough information yet to be certain of that.
Or it may have been an electric field only test.
Here are some papers to look at that have "imperfections" in the system. Electric field only:
http://ssl.mit.edu/publications/theses/ ... Thomas.pdf
http://ssl.mit.edu/publications/theses/ ... chCarl.pdf
Please explain why a virtual grid would operate differently than a physical grid.
And yet if you look at the plasma pictures available from EMC2 it appears that star formation happens there too. Of course we do not have enough information yet to be certain of that.
Or it may have been an electric field only test.
Here are some papers to look at that have "imperfections" in the system. Electric field only:
http://ssl.mit.edu/publications/theses/ ... Thomas.pdf
http://ssl.mit.edu/publications/theses/ ... chCarl.pdf
Please explain why a virtual grid would operate differently than a physical grid.
Engineering is the art of making what you want from what you can get at a profit.
chris,
It appears that the fluxes are self organizing. That is they all expand and contract at the same time. Perhaps there is some mechanism that naturally equalizes the flows. Maybe it is second or third order but enough to do the job.
What is commonly referred to as emergent behavior of systems not predicted by first order looks.
A good place to start would be to find an explanation for star formation in fusors. Rather interesting that this phenomenon has been known for quite some time and yet no one has looked for an explanation. Once that is understood in an electric field only situation then a look to see if it applies to the electric/magnetic field virtual grid situation would be in order.
If the system is self organizing fueling asymmetry may not be a problem.
It appears that the fluxes are self organizing. That is they all expand and contract at the same time. Perhaps there is some mechanism that naturally equalizes the flows. Maybe it is second or third order but enough to do the job.
What is commonly referred to as emergent behavior of systems not predicted by first order looks.
A good place to start would be to find an explanation for star formation in fusors. Rather interesting that this phenomenon has been known for quite some time and yet no one has looked for an explanation. Once that is understood in an electric field only situation then a look to see if it applies to the electric/magnetic field virtual grid situation would be in order.
If the system is self organizing fueling asymmetry may not be a problem.
Engineering is the art of making what you want from what you can get at a profit.
I'm not aware that I have suggested it will. (Though that might be another post.)MSimon wrote:
Please explain why a virtual grid would operate differently than a physical grid.
I have not made any statement in this thread that would undermine the generation of small numbers of neutrons, either from Polywell or from a fixed gridded fusor.
(A fusor has no prospect of generating fusion power and I know of no current proponents who can rationally argue that it might. The difference in this regards to a Polywell is therefore its proponents rather than the device itself!)
The issue I am raising here is that once you try to run up to 'real' fusion power, you are THEN talking about some serious ion fluxes. In these little pocket experiments, there's no noticeable magnetic effects from the flux of fuel ions. What I am contending is that, surely, there WILL be if fusion power is actually achieved. This is not a scale-able attribute - the magnetic field will either work to confine electrons, or it won't. If it disrupted to the point that it no longer works to confine, the device fails.
Please explain star formation. I'm a mere engineer and it is beyond my abilities.chrismb wrote:I'm not aware that I have suggested it will. (Though that might be another post.)MSimon wrote:
Please explain why a virtual grid would operate differently than a physical grid.
I have not made any statement in this thread that would undermine the generation of small numbers of neutrons, either from Polywell or from a fixed gridded fusor.
(A fusor has no prospect of generating fusion power and I know of no current proponents who can rationally argue that it might. The difference in this regards to a Polywell is therefore its proponents rather than the device itself!)
The issue I am raising here is that once you try to run up to 'real' fusion power, you are THEN talking about some serious ion fluxes. In these little pocket experiments, there's no noticeable magnetic effects from the flux of fuel ions. What I am contending is that, surely, there WILL be if fusion power is actually achieved. This is not a scale-able attribute - the magnetic field will either work to confine electrons, or it won't. If it disrupted to the point that it no longer works to confine, the device fails.
BTW I have never suggested that a fusor was anything other than an interesting experimental device. However, star formation does not seem to evolve from your theory of operation. So perhaps we could start from what we SEE. Explain that. And then determine if it scales.
Engineering is the art of making what you want from what you can get at a profit.
I wasn't aware that there is any great mystery. Ions start reciprocating through the grid and many get knocked out. Preferentially, they will fall into the minimum potentials through the centres of the openings. Those that are off centre or deviate from a persistent beam through the centre will get knocked out by the grid. Some survive into persistent beams, most fail.MSimon wrote:chris,
A good place to start would be to find an explanation for star formation in fusors.
None of this is relevant to the Polywell. Particles are proposed to reciprocate in all angles.
For neutron-producing fusors without beams, you will find experiments have been done with a needle cathode, in which the highest charge is at the tip and, thus, ions have nothing much to collide with, except each other.
http://www.fusor.net/board/view.php?bn= ... 1203371007
This appears to work quite well, in fact, with fusion occuring at the smallest drive voltage of any IEC device I know of. However, at higher drive it begins to loose ground on gridded fusors. Within this current discussion, I could easily view this as potentially demonstrating self-interference between slightly-unbalanced ion streams that degrades performance, but that would just be speculation.
I imagine the ion streams in a Polywell would look like the picture in that thread. This experiment appears to have been producing up to 5000 neutron counts per minute, 3He detector, (26,000neuts/s) continuous mode, not 3 in a short pulse, so the experimentors should be given due credit for accomplishing a performance standard that the Polywell has yet to reach.
So, if you want me to guess what a functioning Polywell would look like, it would look like that. No beams, just a central ball of 'stuff'.
Not sure what this has to do with the problems of managing megaAmp ion fluxes, though. Back to the question - is a 1% difference between hemispherical fluxes so unreasonable?
best regards,
Chris MB.
Can we try to be civil, please?(A fusor has no prospect of generating fusion power and I know of no current proponents who can rationally argue that it might. The difference in this regards to a Polywell is therefore its proponents rather than the device itself!)
Again, there is no magnetic field in the core.As a ball-park estimate, with the permeability set as in a vacuum at 1.26E-7 T.m/A, then we'd get 0.01T.m of magnetic moment, or 1T across the core's radius of 1cm. That is, comparable, and therefore disruptive, to the central core's field.
Those were only from WB-6; there were also earlier tests of other machines that also produced neutron counts. We do not know what neutron counts WB-7 produced.I imagine the ion streams in a Polywell would look like the picture in that thread. This experiment appears to have been producing up to 5000 neutron counts per minute, 3He detector, (26,000neuts/s) continuous mode, not 3 in a short pulse, so the experimentors should be given due credit for accomplishing a performance standard that the Polywell has yet to reach
Valencia is a good place to start if you're interested in Polywell basics.
http://www.askmar.com/ConferenceNotes/2 ... 0Paper.pdf
Sorry, I think you may have taken the inverse of what I said! I was trying to say that proponents of fusion power fusors do not have a rational argument, whereas Polywell proponents do; this being the difference I comment on.TallDave wrote:
Can we try to be civil, please?
The debates over whether the 'standard' layout fusor can produce fusion power is long over. It has been investigated to a considerable degree and the general efficiencies have been repeated many times in different experiments. For that reason, because there have been so many successful neutron producing fusor experiments, a realistic perspective on the likely peak performance that can be reached and the answer is; no chance of fusion power. Whereas Polywell does not have that wealth of experimental data and so does not yet enjoy such a detailed perspective. The debate on whether it is viable or not is therefore still 'rational', but in point of fact that can be said *because* of a lack of experimental results, hence the debate remains.
I have formed no strong opinions of the actual arguments being presented to me here yet. They *have* been rational arguments, so I'm chewing over them. But being rational does not, in itself, demonstrate correctness and/or a realistic analysis of what will happen at scale.
I have already received further enlightenments on Polywell within these posts so there is more to consider.
Apologies, again, for the grammar, where it has given an unintended inference.
best regards,
Chris MB.
Well, thanks for clarifying.
Many of us are skeptical the Polywell design can produce net fusion power, esp. in a p-B11 scheme. There are all sorts of things that could go wrong in scaling from WB-6/7 to WB-100. I think proponents would generally say they just haven't seen any well-supported objections that totally rule out the device from working (though many are problematic), given what we know from the WB series of devices.
For myself, I think that Polywell's promising enough to deserve the $200M over 5 years in funding that would allow Nebel, Park, and company to build a 1.5M radius device and see what they can do with it.
The thing Polywell has going for it is that if it does work, it's likely to be an economically viable power source within a reasonable time frame. As long as we are spending billions on approaches for which we already know this is not the case, it makes sense to try this.
Many of us are skeptical the Polywell design can produce net fusion power, esp. in a p-B11 scheme. There are all sorts of things that could go wrong in scaling from WB-6/7 to WB-100. I think proponents would generally say they just haven't seen any well-supported objections that totally rule out the device from working (though many are problematic), given what we know from the WB series of devices.
For myself, I think that Polywell's promising enough to deserve the $200M over 5 years in funding that would allow Nebel, Park, and company to build a 1.5M radius device and see what they can do with it.
The thing Polywell has going for it is that if it does work, it's likely to be an economically viable power source within a reasonable time frame. As long as we are spending billions on approaches for which we already know this is not the case, it makes sense to try this.
chris,
You are new to the discussion so I will forgive your mis-understanding. The fusor has been discarded as anything but an experimental tool (it has its uses) approximately 2 years ago by those involved in the discussion (myself included).
If you study fusor design the shape and openings of the grid don't seem to have much effect on star formation. In addition the star effect seems to involve bunching. Which is (as I'm sure you are aware) an annealing mechanism. This can be verified (to a certain extent) by the production of RF at discrete frequencies.
You will also see in simulations that the beams tend to interact in such a way that they all exit the core at the same time and re-enter at the same time. This seems counter intuitive to me. Why not opposing beams in phase opposition? (one entering while the opposite is leaving)
So no - I don't think a disparity of even 1% is likely in a self organizing system.
This self organization (other than POPS) has never been explained satisfactorily to me. Why beams? Why 6 beams? Why not an oscillating sphere? Certainly grid focusing might be an answer. That still begs the question of why not an oscillating sphere?
Now Rick Nebel does not think beams are that important (at least as he has communicated here). I am of a different opinion. No doubt sufficient data will resolve the questions. I am also of the opinion that resolving the questions in a BFR configuration will require a continuously operating (seconds to minutes) test reactor. A device that will cost (along with associated power supplies) on the order of $5 to $20 million. Cheap compared to what we used to throw at ITER every year.
Doc Bussard thought the annealing mechanism was edge energy interchange. I think it is bunching (a klystron type effect). We shall see.
And I think work on fusors to understand more of how the plasma works in a purely electric field would have a lot of uses. Water cooled grids might get the currents up into the hundreds of milliamps to amps range. Such an increase (over the current milliamps to tens of milliamps) could probably tell us a lot about scaling problems. The point being - not power generation but study of plasma effects.
You are new to the discussion so I will forgive your mis-understanding. The fusor has been discarded as anything but an experimental tool (it has its uses) approximately 2 years ago by those involved in the discussion (myself included).
If you study fusor design the shape and openings of the grid don't seem to have much effect on star formation. In addition the star effect seems to involve bunching. Which is (as I'm sure you are aware) an annealing mechanism. This can be verified (to a certain extent) by the production of RF at discrete frequencies.
You will also see in simulations that the beams tend to interact in such a way that they all exit the core at the same time and re-enter at the same time. This seems counter intuitive to me. Why not opposing beams in phase opposition? (one entering while the opposite is leaving)
So no - I don't think a disparity of even 1% is likely in a self organizing system.
This self organization (other than POPS) has never been explained satisfactorily to me. Why beams? Why 6 beams? Why not an oscillating sphere? Certainly grid focusing might be an answer. That still begs the question of why not an oscillating sphere?
Now Rick Nebel does not think beams are that important (at least as he has communicated here). I am of a different opinion. No doubt sufficient data will resolve the questions. I am also of the opinion that resolving the questions in a BFR configuration will require a continuously operating (seconds to minutes) test reactor. A device that will cost (along with associated power supplies) on the order of $5 to $20 million. Cheap compared to what we used to throw at ITER every year.
Doc Bussard thought the annealing mechanism was edge energy interchange. I think it is bunching (a klystron type effect). We shall see.
And I think work on fusors to understand more of how the plasma works in a purely electric field would have a lot of uses. Water cooled grids might get the currents up into the hundreds of milliamps to amps range. Such an increase (over the current milliamps to tens of milliamps) could probably tell us a lot about scaling problems. The point being - not power generation but study of plasma effects.
Engineering is the art of making what you want from what you can get at a profit.