Q&A : Major hurdles to overcome for Polywell Reactors

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

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energyfan
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Post by energyfan »

didnt want to open a new thread just for this, here's something that i was asked :
How wide is the vacuum chamber in WB7? And how wide is the centre sphere?

I didnt think of checking the WB6/WB7 sizes. There are some numbers given above about coil dimensions, will those values give a size for the vacuum chamber ?

tonybarry
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Post by tonybarry »

Much smaller than WB6; though the exact dimensions are not available to my knowledge.

A picture of WB6 is available on the EMC2 web page, and if you consider the coil dimension is 300mm, you should be able to deduce the chamber dimensions from that. I estimate it is over a metre diameter.

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Tony Barry

Roger
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Post by Roger »

Keegan wrote:Yep ! Cant believe nobody has mentioned them yet.
Oh yeah we covered 'em a ways back..

http://web.mit.edu/fbml/

I think some MIT guys took notice.
I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

OrionCA
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Re: Q&A : Major hurdles to overcome for Polywell Reactor

Post by OrionCA »

energyfan wrote:What are the major hurdles in making a Polywell work right now (besides the obvious size of the machine). What are there obstacles that one might face while trying to reach break-even ? And as far as theory goes, did Dr. Bussard/anyone else face any problems while developing the process on paper ?

I thought that one of these Q & A might be useful here when I was browsing through the older threads and noticed theres a lot of one-time questions that had whole threads devoted to them. Since I dont get very much of whats going on with the WB's , I will probably be asking a lot of questions and this seemed a simpler way to do it.
Discouraging terrorists from crashing hijacked airliners into the reactor just to see what would happen. Of course, that problem is WAY down the road from here. :D

Somewhat more seriously, all those process-flow control elements that differentiate between (1) a reactor that you feed fuel into to get useful energy out plus waste products, and (2) a bomb. It's a lot easier to make a device that goes *boom* than one that doesn't. Start with the fuel. Has to be available in sufficient quantities and quality to make building the thing worth the effort. You have to feed it into the reactor at an optimum rate for fusion w/o causing sputtering, overload, or other undesirable characteristics. The fusion has to be contained for the duration of the reaction and the waste products vented and disposed of safely. Whatever energy you derive from the reactor has to be successfully integrated into the electrical grid. Every element of the process has to be analyzed, mapped, modeled, and engineered to ensure you have a working production reactor instead of an interesting science fair project (or a bomb). Focusing on one element or another isn't going to get you there - we can always make stronger magnets or wrap them in better insulation or adjust the fuel mixture to overcome sputtering, etc. Integrating all those elements into a working, production reactor after the WB's demonstrate fusion will be the hard part and will cause a lot of engineers a lot of sleepless nights.

drmike
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Re: Q&A : Major hurdles to overcome for Polywell Reactor

Post by drmike »

OrionCA wrote: Integrating all those elements into a working, production reactor after the WB's demonstrate fusion will be the hard part and will cause a lot of engineers a lot of sleepless nights.
I sure hope so! Proving the physics is still a hard problem. Once we've got that, the engineering will be worth losing sleep over.

hanelyp
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Re: Q&A : Major hurdles to overcome for Polywell Reactor

Post by hanelyp »

OrionCA wrote:Somewhat more seriously, all those process-flow control elements that differentiate between (1) a reactor that you feed fuel into to get useful energy out plus waste products, and (2) a bomb.
Too much bad sci-fi out there. Worst boom I can see coming from a polywell is on the order of the electrical equipment shorting out. Vary operating conditions almost direction from optimum and the reaction slows down for one reason or another. The only exception I see to that is excessive drive voltage, a really easy error to avoid.

eros
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Post by eros »

Keegan wrote:Yep ! Bitter magnets are a great design. Cant believe nobody has mentioned them yet. Will be great in a test reactor with CU and liquid cooling. Sadly very hard to apply to Super Conductors.
You can't owercome copper resistivy. That means you need enormous power to drive magnets. Breakeven ~imposible with copper magnets or things grow very big. - but check my calculations I hope they are wrong.
</ Eerin>

MSimon
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Post by MSimon »

eros wrote:
Keegan wrote:Yep ! Bitter magnets are a great design. Cant believe nobody has mentioned them yet. Will be great in a test reactor with CU and liquid cooling. Sadly very hard to apply to Super Conductors.
You can't owercome copper resistivy. That means you need enormous power to drive magnets. Breakeven ~imposible with copper magnets or things grow very big. - but check my calculations I hope they are wrong.
Coil loss grows linearly with size. Power out goes up at some higher power.

Break even will happen when the size is big enough.

===

Coil area goes up as the 2nd power of size. At constant current per unit area losses go up linearly with size. Magnet field will go up linearly with size (amp turns -i.e. coil area)/(linear size). Power out goes up with volume of reaction space. It goes up as the 3rd power of of linear size. Power goes up as the 4th power of the magnetic field.

So coil losses go up linearly and power output goes up as the 7th power of linear dimensions.

At some point you reach break even. Make it larger and you get net power.
Last edited by MSimon on Tue Nov 11, 2008 12:52 am, edited 1 time in total.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
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Post by MSimon »

Keegan,

I mentioned the Bitter design in March or April of '07 at NASA Spaceflight.
Engineering is the art of making what you want from what you can get at a profit.

eros
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Post by eros »

MSimon wrote:
Coil loss grows linearly with size. Power out goes up at some higher power.

Break even will happen when the size is big enough.
I agree that, but questions is how big it needs to be and how much energy it consumes in coils at breakeven. Do calculation that I don't need to brother anymore are my calculations correct.
MSimon wrote:
===

Coil area goes up as the 2nd power of size. At constant current per unit area losses go up linearly with size. Magnet field will go up linearly with size (amp turns -i.e. coil area)/(linear size). Power out goes up with volume of reaction space. It goes up as the 3rd power of of linear size. Power goes up as the 4th power of the magnetic field.

So coil losses go up linearly and power output goes up as the 7th power of linear dimensions.

At some point you reach break even. Make it larger and you get net power.
Don't lost factor that when size grows cross area grows ^2 so wire lengt grows and its amount grows. To keep same B rule says that you have to divide wire lenght so need more amperes. P=rI^2

that comes power needs grows r^2 vs fusion power r^3.

Total scaling law seems to be r^1 (?) with resistive coils and constant B.

wikipedia: B=4pii*10^-7 * NI/L

I am sorry and please show that I am wrong.
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Torulf2
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Post by Torulf2 »

CNT is said to be a far better conductor than Cu. Are there any tests for CNT magnets?

eros
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Post by eros »

Torulf2 wrote:CNT is said to be a far better conductor than Cu. Are there any tests for CNT magnets?
I can't find yet, but this says -50% resistivity:

http://www.springerlink.com/content/j2ucrg72gwqd97e3/

However price must be high. Nanotubes are quite expensive. MgB2 is quite cheap..

in 10m machine -50% resistivity seems drop needed B to 20T and breakeven occur 540GW power level.
Significant improvement.

But superconductors really pay them price and fast. at electricity price 0.1$/kwh 540GW cost 54 000 000$ per hour..
</ Eerin>

Orionblade
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Why not go small?

Post by Orionblade »

And use large permanent magnets.

Supermagnetman has a halbach array that puts 3T into about a cubic centimeter.

This is the route I'm going for a demo of electron trapping in low pressure argon. I just want to visualize the electrons and plasma behavior, and not have to worry about neutrons.

Will report back when I have my mill up and running and cranking out parts.
When you have a Cray II for a brain, you wish your body had more clock cycles available...

tonybarry
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Post by tonybarry »

It will be good to hear the results.

Regards,
Tony Barry

MSimon
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Re: Why not go small?

Post by MSimon »

Orionblade wrote:And use large permanent magnets.

Supermagnetman has a halbach array that puts 3T into about a cubic centimeter.

This is the route I'm going for a demo of electron trapping in low pressure argon. I just want to visualize the electrons and plasma behavior, and not have to worry about neutrons.

Will report back when I have my mill up and running and cranking out parts.
You can't use permanent magnets. I'm not going to go into the arguments. This has been hashed and rehashed.

However, you will get a good visualization of the electrons and plasma behavior. The burn marks will tell the story.
Engineering is the art of making what you want from what you can get at a profit.

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