looking for an equation, where is the main FAQ for polywell?

Discuss how polywell fusion works; share theoretical questions and answers.

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ohiovr
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looking for an equation, where is the main FAQ for polywell?

Postby ohiovr » Sun Mar 29, 2009 1:05 am

I have heard the claim that 9 neutrons were detected in a milisecond pulse operation of a .3 meter diameter polywell and about a miliwatt of power output was achieved with a 10,000 watt power input. There is a claim of a power scaling law (imo pretty bold to call it a law yet with not a single confirmation anywhere) that would yield a net of a gigawatt of power with a polywell that has a 10 meter diameter. Correct my facts so far as I've gathered them from a lot of unofficial sources.

This is supposed to flow from the 7th power of the diameter. And? I need a real equation that I can plug in and find the numbers myself. 1 gigawatt to 10 meters? How much power from 10.1 meters? or 9.9 meters? where does it fail to net and begin to net?

So could someone give me me an equation I could evaluate myself in the spread sheet of my choice?

Also I have tons of questions about polywell and its problems, solutions, and claims. Where is
the FAQ? Polywell should have a deep wiki by now. Where is that?

I am a layperson. I can figure out how much energy there is in a gram of a particular thermonuclear fuel if it is completely spent but I have little to no idea how to obtain the conditions required for achieving controlled fusion.

It is encouraging to think that someone from los Alamos gave up his day job to take over this endeavor I really want to believe in it.

I am skeptical of it has any chance of being commercially interesting but if it has even 1 in 100,000,000 it will work as theorized it is still a more viable solution to tokamak which has exactly 0 chance of it ever being commercially viable.

Billy Catringer
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Postby Billy Catringer » Sun Mar 29, 2009 3:11 am

Some of us have been trying to work up a FAQ. Why don't you post your list of questions since you are newly exposed to the subject. Then we will have a useful list to work from.

D Tibbets
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Postby D Tibbets » Sun Mar 29, 2009 3:37 am

A lengthy thread discussed the Polywell at the link below. read through the messages, paying peticular attention to the comments by Tom Ligon. He has alot of insite as he worked with Dr Bussard at one time.

http://www.fusor.net/board/view.php?bn= ... ywell&st=0

As far as the scaling laws: power output scaling as B^4 * R^3 is well accepted in plasma physics. There are arguments weather they fully apply to the Polywell, especially the B (magnetic field strength) scaling. Also, there is debate weather the loss scaling of R^2 (or is it B^2, or R^2 + B^2...?) is reasonable.


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

ohiovr
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Postby ohiovr » Sun Mar 29, 2009 5:40 pm

Well if someone, anyone can explain the math on how a ten meter reaction vessel can yield 1 gigawatt of thermonuclear reactions I'd greatly appreciate it. Then maybe I could figure out on my own how much power a 10.1 meter reaction vessel could yield or a 9.9 meter vessel.

Billy: I'm working on a list of questions pertaining to the polywell per your request. I'll post it here when I am done.

-Scott

TallDave
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Postby TallDave » Sun Mar 29, 2009 7:07 pm

Actually, I just did a post on that.

Mine is for 100MW, but the math is similar.

Of course, a 1GW reactor would probably be limited in smallness by the ability of materials to withstand the energy density. You probably have to go as r^2 from 100MW.

KitemanSA
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Postby KitemanSA » Sun Mar 29, 2009 8:07 pm

TallDave wrote:Actually, I just did a post on that.

Mine is for 100MW, but the math is similar.

Please correct your math. In D-D, each TWO fusions create ONE neutron, not the other way around as you have it in your post. DrB stated he approximated 1E9 fusions per second in his Valencia paper.

In your blog you also mention well depth, but it seems there would be a trade-off between well depth and density at a specific B. Just a thought.

By the by, I agree we need a FAQ but Joe is hesitant to put in a FAQ forum for some reason. Maybe we can encourage him.

ohiovr
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Postby ohiovr » Sun Mar 29, 2009 9:09 pm

yes tallDave this is the exercise I am looking for

So, now for the math. The WB-6, Bussard’s last experimental model, at about .15 meters in radius and .1T magnetic field strength, was estimated to produce 1e9 neutrons from a deuterium plasma, for a fusion rate of 5e8 (each fusion produces two electrons neutrons). Since we could, opimistically, hope to burn a deuterium-tritium mix in an actual net power reactor, we can substitute in the 68 times better fusion rate of a D-T mix and get a rate of 3.4e+10 fusions per second. Each D-T fusion reaction produces about 17.6Mev of energy, and there are about 1.6E19 eV in a joule, and so we end up with about .09588 watts (a watt is a joule per second) at WB-6 size. Now, scaling up to 10 times that size, we get 10^3 for the increase from volume (ten times the original radius), and if we increase B to 3.2T, we gain another 32^4. Thus we have .09588 * 10^3 * 32^4 = 100,537,467 watts of glorious burning fusion, suitable for powering a Navy destroyer or lighting your neighborhood.


When you say "scaling up to 10 times that size" what do you mean by that? Is that the radius or the volume? The volume of a sphere is 4/3*PI()*r^3 not just r^3

where does the .1 testla magnetic field come to be a 3.2 testla field? Isn't more current and voltage required for that? Why 3.2 and not 3.1 or 3.3?

Obviously there is a power input to this machine. How much power input to get 1 megawatt out? If it is a hundred megawatts this just isn't going to fly.

Aero
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Postby Aero » Sun Mar 29, 2009 10:07 pm

Obviously there is a power input to this machine. How much power input to get 1 megawatt out? If it is a hundred megawatts this just isn't going to fly.

That is the question. That is the reason Dr. Nebel, et. al. are still doing experimental work. If the answer were known to within a reasonable error factor then they would be building a large scale prototype, or, on the down side, moving on to other things.
The input power needs to replace the energy losses which occur in the form of lost electrons and lost ions (if any). Supercooled magnets don't use power during operation. (They do require refrigeration). "Power in" is the topic of several threads on this forum, I suggest a search.
Aero

TallDave
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Postby TallDave » Mon Mar 30, 2009 2:01 am

In D-D, each TWO fusions create ONE neutron, not the other way around as you have it in your post.


Oops, I do seem to have that backwards. Looking at the nuclear fusion wiki there should be a 50/50 branching D-D reaction, with a neutron on only one branch.

http://en.wikipedia.org/wiki/Nuclear_fusion

DrB stated he approximated 1E9 fusions per second in his Valencia paper.


He does say that, but the Polywell wiki cites a more official source that has it as 1e9 neutrons. I haven't checked the source. It's probably just that wide confidence interval again.

KitemanSA
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Postby KitemanSA » Mon Mar 30, 2009 2:46 am

TallDave wrote:
DrB stated he approximated 1E9 fusions per second in his Valencia paper.
He does say that, but the Polywell wiki cites a more official source that has it as 1e9 neutrons. I haven't checked the source. It's probably just that wide confidence interval again.
Not anymore. The error in Wiki has been corrected. Both references cite 1E9 fusions per second.

KitemanSA
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Postby KitemanSA » Mon Mar 30, 2009 4:32 pm

ohiovr wrote: Obviously there is a power input to this machine. How much power input to get 1 megawatt out? If it is a hundred megawatts this just isn't going to fly.
DrB in a variety of sources has stated "net power" 100MW, and ~40MW input (IIRC) with the 1.5 - 2.0m radius machine. It is not clear if that is net 100MW or gross 100, net 60. Either way, the step from one to the other is a matter of SMALL size changes.

In his Valencia paper DrB does mention in some detail the scaling of the loss mechanisms. But simplistically, it has been published that power scales R^7 while GAIN is R^5. The power is actually B^4*R^3. Please note that these are "all else being equal, simple size scaling" rules. Something that is 10X scale has every linear dimension scaled by 10X. Given this scaling, the B will wind up scaling directly with R, so this becomes R^4*R^3=R^7. However, nobody thinks that it would be wise to scale the WB6 magnet configuration! Thus, folks define other strength levels for their own pruposes. What actually is used will be a function of the trade-offs.

Anyway, if the scaling laws prove true at large scale, then reaching net useful power shouldn't be too hard. Some would say "that's a mighty big IF"!

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Postby Roger » Mon Mar 30, 2009 8:01 pm

DD, 1.5m break even, 2m 1000MW.
PB-11, 2m break even, 3m 1000MW.


1000MW, as in generating 1000MW.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

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Postby KitemanSA » Tue Mar 31, 2009 12:35 am

Roger wrote:DD, 1.5m break even, 2m 1000MW.
PB-11, 2m break even, 3m 1000MW.

1000MW, as in generating 1000MW.
Reference?

TallDave
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Postby TallDave » Tue Mar 31, 2009 4:12 am

I think it's 100MW Roger not 1GW. Anything over 100MW has the problem of materials being able to withstand the energy density.

I also don't think it's a 40MW input for a 100MW output. That wouldn't be very useful. Let me know if you find a cite though. Bussard wasn't too explicit about Q values anywhere that I've seen. It's probably safe to assume he was talking about gross power.

I haven't been able to find it, but I think Rick gave us an estimate of 10MW input power for a 100MW machine at one point. As I remember, he was talking about EMC designs they'd worked up.
Last edited by TallDave on Tue Mar 31, 2009 4:20 am, edited 1 time in total.

TallDave
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Postby TallDave » Tue Mar 31, 2009 4:19 am

Here's a sort-of answer to an earlier question of mine:

In large machines, such as power reactors (typically 2-3 m in diameter) with high power electron drives (e.g. 100 -500 Amps at 15-30 kV for DD and 180-220 kV for pB11),


http://www.emc2fusion.org/RsltsNFnlConc ... 120602.pdf

Point 8 is interesting too.


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