Polywell Parameters

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

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drmike
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Post by drmike »

In the 2006-9_IAC_Paper.pdf Bussard says:
On electron trapping: since the ion density is nearly equal to (and thus set by) the trapped electron density, it is desired to have the highest possible electron density for the least possible drive current. This requires that the transport loss _across_ trapping B fields be small, and their flow _along_ the cusp axies of the polyhedral B fields also be kept small.

That implies the electron temperature is low so the Larmor radius is small and the electrons stay trapped. It would be very interesting to see the mathematical model used to predict the electron density as a function of field strength and current input, and to know what the trapping times are for given field strength. Bussard is supposedly working on writing this all up. Having experience with measured experiments will help develop the model since he'll know what terms to throw away and which to keep.

Since the ions are more massive by a few thousand times, they don't interact with the B field as much. Seeing how much and where the balance points are for optimal performance will be really interesting.

MSimon
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Post by MSimon »

It is my opinion that because of all the interactions going on that anything except the most general calculations will be of little use.

However, I think a properly designed computer with about 1E15 to 1E20 bits could solve the problem.

i.e. do the experiment.

drmike
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Post by drmike »

As an experimentalist I have to agree, but it is still nice to see if you can predict the outcome to some extent. It makes it easier to design similar devices for different applications that way.

Langmuir worked out space charge 100 years ago and Bohm extended it to magnetic fields 60 years ago. There's plenty of good theory that can be applied to a polywell. The people who have done the experiments already can point us in the right direction.

I'm grinding through classical elecrodymanics theory just so I can begin to deal with the polywell set up in a paper and pencil attack. It's slow going, but should be fun. I can't afford hardware for a long time yet.

But pencil and paper and cpu cycles are cheap!

drmike
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Post by drmike »

I've learned a lot about spherical trigonometry attempting to find some simple rules for placing circular coils around a sphere in a uniform way. Every attempt gives some result, but nothing is ever "uniform". For N = 4, 6 or 12 you can get full coverage of a sphere with equadistant centers of circular coils. For any other N you have to resort to some kind of "rule" which leads to a specific set of coil sizes. If the rule is equal areas between coils you get a different result than if the rule is maximum surface area covered.

So last night I'm plotting a bunch of functions and asked myself "why do the coils need to be circular?" The answer is they don't. In one patent I saw from Bussard, he uses "baseball" coils - the same thing used at the end of mirror machines.

Time to take a step back and read up on electromagnetic field theory. Space charge on field lines seems like a great next step - but understanding which rule to apply for coils really depends on what I need the electrons to do.

But I have to admit this is a ton of fun. I never learned spherical trig before, but its applications to navigation and interplanetary travel are obvious. Since Bussard wants to build space ships, it'll come in handy eventually!

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