## Resultant particles hitting ion or electron Injectors

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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chrismb
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Betruger wrote:
chrismb wrote:Sorry to dissapoint. It is several billion passes required before 'an average' fusion event.
Isn't this direct contradiction of Dr Nebel's explicit statement of the 10k passes figure?
I don't know what he said. But that's what 'cross-section' means. How else d'you think 'cross-section' is worked out? It is 1/[density.MFP].

If Dr Nebel declares "10,000 passes" are the words of God, spoken directly to him, then I'd have no way to debate it. Otherwise, show me the calculation....

As per my previous link, if you go around assuming 1/10 atmosphere for the central reaction core, then you could claim anything, really. I think 1E20/m^3 is more than a generous estimate of average, unless and until some striking evidence materialises otherwise.

Just for fun, what is the density assuming it were 10,000passes for 80keV collision energy deuterons? That'd be 20,000m, so density = 1/[(2E4m).(2E-30m^2)] = 2.5E25/m^3. One whole atmosphere of pressure - (as per average 'flight' density experienced by the deuterons). Hey, why bother with a vacuum chamber?!?...That should reduce the project cost considerably!

Betruger
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Just saying.. If it is a contradiction.. It's his word against yours. He has the experimental data and his word is on the line. What about you?

Roger
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2 hours?
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

chrismb
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Betruger wrote:Just saying.. If it is a contradiction.. It's his word against yours. He has the experimental data and his word is on the line. What about you?
It's his word against maths, if it is so. How d'you stick an odometer on an ion to test such a thing 'experimentally'? You'd need to be able to detect fusion events and know how many ions are participating before you can question that maths with experimental results. Fusion cross-section experiments are performed by this very process - beam ions into a target and see how many fusions you get out...
Last edited by chrismb on Mon Jun 29, 2009 9:09 pm, edited 1 time in total.

chrismb
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Roger wrote:2 hours?
Yup. Sorry...

TallDave
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You'd need to be able to detect fusion events and know how many ions are participating before you can question that maths with experimental results
What makes you think he hasn't done that?
I've not offered any equations with 'density' and 'reaction rate' in it. But if the density increases, the MFP to fusion decreases, the number of reciprocations across the space decreases (what you're talking about is embedded in that 'line') so the time to fusion decreases.
I'm not sure why you would do a calculation without density, or how it could be meaningful.

Anyways, Rick did a calc way back on what Polywell densities might be with giant magnets comparable to ITER's.
rnebel wrote:The 2.5e22 density is what is required to achieve Beta = 1 on a big machine.
As per my previous link, if you go around assuming 1/10 atmosphere for the central reaction core, then you could claim anything, really.
Indeed. Why, you might even claim to have a working fusion reactor design.

You have to be careful with applying Lawson's to a Polywell. Lawson's assumes a Maxwellian distribution when it calculates the fusion rate. Also, it has to do with ignition, which doesn't apply to a Polywell at all.

chrismb
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TallDave wrote:
You'd need to be able to detect fusion events and know how many ions are participating before you can question that maths with experimental results
What makes you think he hasn't done that?
Because've what hasn't been said.
TallDave wrote:
I've not offered any equations with 'density' and 'reaction rate' in it. But if the density increases, the MFP to fusion decreases, the number of reciprocations across the space decreases (what you're talking about is embedded in that 'line') so the time to fusion decreases.
I'm not sure why you would do a calculation without density, or how it could be meaningful.
I did, of course. It just didn't appear on the same line as 'reation rate' so I don't think Dan spotted it.
TallDave wrote: Anyways, Rick did a calc way back on what Polywell densities might be with giant magnets comparable to ITER's.
rnebel wrote:The 2.5e22 density is what is required to achieve Beta = 1 on a big machine.
Extraordinary claims require extraordinary proof. Sure, if 1millibar can be achieved then the numbers change. Only 10million recirculations. Rewind and note I said that these numbers would have to be done with an early DD version, if there were ever to be any funding to get to machines working to these fantastical specifications. So the question remains, for WB-7/8, these must surely be relying on these lower energy, lower density environments, with DD. What'd'you think the success will be if the deuterons need to average 7000s residence? Which in turn implicitly asks; what'd'you think the chances of the next phase of machines is?
TallDave wrote: Indeed. Why, you might even claim to have a working fusion reactor design.
Many have claimed such a thing. Even Culham itself with Zeta? None have yet succeeded. The odds are not good for those who merely 'claim'. On Polywell, we hope, we wait, the clouds roll by in the wind, and we wait a little longer - for something, anything, a shred of tiny information. I'm hopeful, I just sound like an old croaky, but I am hopeful and wish it well. Never said anything different. I'm just trying to face reality, and perhaps by me pointing out issues, others will see solutions. I don't, at this time.
TallDave wrote: You have to be careful with applying Lawson's to a Polywell. Lawson's assumes a Maxwellian distribution when it calculates the fusion rate. Also, it has to do with ignition, which doesn't apply to a Polywell at all.
Not used it. I don't see it is relevant to Polywell and wouldn't use it. I seem to recall Art and I bashing that one around some time ago. Not sure why you've raised it.

TallDave
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Because've what hasn't been said.
Sorry, what are you saying hasn't been said? I think we were told at one point they had neutron detectors.
What'd'you think the success will be if the deuterons need to average 7000s residence? Which in turn implicitly asks; what'd'you think the chances of the next phase of machines is?
Philistine that I am, I like to work back from experimental evidence. Could WB-6, WB-4, and PLZ-1 have gotten the fusion counts they did if the reaction rate was what you claim?
Many have claimed such a thing.
Sure. My point is just that any design that claims to be a working fusion reactor is going to have some extraordinary components almost by definition.

Now, if you tell me you have fractional quantum states of an electron, I am going to be very skeptical. If you are merely claiming to have a high-beta fusion device, I will be interested.

Do you have some physical objection to Rick's calculation?

Someone had mentioned Lawson's below, I just wanted to issue a caveat there.

chrismb
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TallDave wrote:Could WB-6, WB-4, and PLZ-1 have gotten the fusion counts they did if the reaction rate was what you claim?
Sure. From fast neutrals bombarding a wall permeated through by deuterium.

D Tibbets
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chrismb wrote:
D Tibbets wrote: As I interpret your formula you are saying that mean distance to a fusion event = 1 / density X Barns. The mean free path decreases as the density increases, but the collision rate would increase, so shouldn't the density be in the numerator?
I've not offered any equations with 'density' and 'reaction rate' in it. But if the density increases, the MFP to fusion decreases, the number of reciprocations across the space decreases (what you're talking about is embedded in that 'line') so the time to fusion decreases.

D Tibbets wrote: When less generous interactions than you granted are present there is still alot of wiggle room befor you reach the ~ 10,000 passes needed for effective fusion that I have seen quoted. The corresponding required lifetimes (in seconds) of the ions at 20KeV well depths are quite small ( millisecond time scales?).
Sorry to dissapoint. It is several billion passes required before 'an average' fusion event.

D Tibbets wrote: If I'm completly confused ( only a short distance need be traveled befor that reaction can occur ) there still seams to be a problem with your final calculation. 2.5 billion reciprocations / ~2.8 million reciprocations / seconds = 900 seconds. This is nearly an order of magnitude lower.
I've calculated a) how many reciprocations are needed before an 'average' fusion event, and b) the time-of-flight of one of those reciprocations. Total time to fusion is therefore (a) x (b). Not sure what you are thinking of with your denominator. I will go back and edit in the units, it seems to have caused confusion without them.
A site that deals with figuring the fusion rate for helium in a grided fusor. The final answer, if the analysis is accurate involves more than just the MFP. eg the recirculation contribution may be more than linear. And the degree of focus can change the results.
http://www.diane-neisius.de/fusor/index_E.html#fus

My shaky calculation of a deuteron ion at 20 KeV gives a speed of ~ 1.5 million meters/sec, or ~ 1.5 million transits per second of a 1 meter diameter machine. As a check on my number a link to a similar solution (once eV to Joule conversion is done)

I don't know if you figured less than 100 % potential into kinetic energy conversion within the 0.5 meter well depth. That would lower the number.
Also, if the fuel is almost fully ionized as I believe is recognized as a prerequisite for the machine to operate successfully, in addition to some degree of focusing, then the net ion interactions would be beam-beam, not beam-target so the effective velocities would be doubled (admittedly this effects the crossection, not velocity of any particular particle).

Finally, I'm guessing your interactions are the random collisions within your volume. With focus to some significant degree the dynamics are different. Again see the first link.

I suspect the large number for the deuteron lifetime before a fusion event is not the final answer, as I previously hinted at in my previous post. The density of other fuel ions should have a positive effect on the fusion rate as the density/ absolute numbers increase. My impression is that your 2.5 billion meter distance before a particular deuteron reacts with any of the other deuteron's is only a fraction the overall picture. You have to consider what all of the deuteron's are doing in total. As an example of my reasoning, consider the Sun. The lifetime of a particular hydrogen (proton) in the Sun's core is ~ 10 billion years before it reacts. But, because of the tremendous number of hydrogen ions present the final fusion is a little more than 1 per 10 billion years. ie- the crowd effect adds up.

I know I'm not articulating my arguments well. The basis of my discomfort with your analysis is that the MFP~= reation rate. You have the reaction rate droping as the density increases because the density is in the denominator. There has to be some other consideration or it doesn't make sense , at least not to me. How would your calculation fit with the reported results of JET?

Dan Tibbets
To error is human... and I'm very human.

D Tibbets
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chrismb wrote:
D Tibbets wrote: As I interpret your formula you are saying that mean distance to a fusion event = 1 / density X Barns. The mean free path decreases as the density increases, but the collision rate would increase, so shouldn't the density be in the numerator?
I've not offered any equations with 'density' and 'reaction rate' in it. But if the density increases, the MFP to fusion decreases, the number of reciprocations across the space decreases (what you're talking about is embedded in that 'line') so the time to fusion decreases.
"So the mean distance to a fusion event would be 1/[(1E20/m^3).(2E-30m^2)]=5billion metres".
Since you are granting that every collision would be head on, with a resultaant fusion probability represented by the Barns, you are essentially saying that "mean distance to a fusion event" is directly proportional to the MFP(or at least that is how I am reading it). And, what is (1E20/m^3) if not a measure of density? I'll welcome any clearification.

Dan Tibbets
Last edited by D Tibbets on Wed Jul 01, 2009 3:35 pm, edited 1 time in total.
To error is human... and I'm very human.

chrismb
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mmff... Of COURSE I've included density. I've just not included them *in one single equation*

chrismb
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D Tibbets wrote: You have the reaction rate droping as the density increases because the density is in the denominator. There has to be some other consideration or it doesn't make sense , at least not to me. How would your calculation fit with the reported results of JET?
I've no idea what you're talking about here, Dan. Sorry, this isn't what I've said at all. The definition of 'cross-section of some event' involved the average distance 'to some event' and the density of the reactants involved in that event. Look again at the way I've done the calc. The reaction rate is only done in the very last line, long after I've dealt with MFP to fusion, and density. By then, by the end of the calc, the numbers that you think you're looking at have effectively ended up upside down.

Why you think I need to reconsider *my* objective figures just because the conclusion doesn't come out as someone else's subjective presumption is an odd logic to follow.

MSimon
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chrismb wrote:
D Tibbets wrote: You have the reaction rate droping as the density increases because the density is in the denominator. There has to be some other consideration or it doesn't make sense , at least not to me. How would your calculation fit with the reported results of JET?
I've no idea what you're talking about here, Dan. Sorry, this isn't what I've said at all. The definition of 'cross-section of some event' involved the average distance 'to some event' and the density of the reactants involved in that event. Look again at the way I've done the calc. The reaction rate is only done in the very last line, long after I've dealt with MFP to fusion, and density. By then, by the end of the calc, the numbers that you think you're looking at have effectively ended up upside down.

Why you think I need to reconsider *my* objective figures just because the conclusion doesn't come out as someone else's subjective presumption is an odd logic to follow.
Your figures are as objective as your assumptions.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
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chrismb wrote:
TallDave wrote:Could WB-6, WB-4, and PLZ-1 have gotten the fusion counts they did if the reaction rate was what you claim?
Sure. From fast neutrals bombarding a wall permeated through by deuterium.
Care to do the calculations to get some idea of the relative densities (fast neutrals - deuterium permeated walls) that might give rise to the detected neutron counts?

Assume a detector efficiency ( intercept area, quantum efficiency, etc) of 1/10,000 to 1/20,000. Assume a reaction time of 250 uS. Now what has to be going on between the walls and neutrals to get between 1 and 6 neutrons?

BTW how do you get the D ions neutralized before they hit the wall with 200 KeV?
Engineering is the art of making what you want from what you can get at a profit.