A few questions on Polywell facts and figures.

[chrismb]

this strength is way to small to stop/ divert the much heavier ions.
Dan Tibbets

What magnetic field do you think is there, then? I have demonstrated above the arithmetic to show that a field of 0.05T is all that is required to arrest the motion of a proton towards a 110kV potential over a distance of 1m.

If it expereinces any 1T fields that are aligned at anything more than cos-1(0.05)=~3degrees from a radial then it will experence a normal magnetic field of 0.05T.

As I previously said, I cannot see why there is such an instant cut-off of field, to which was replied that the proton did not go through a magnetic field, which now seems to be not correct. I think the answer should have been it *does* go through a field but it isn't thought to deflect the proton.

So, is it 'no magnetic field' or is it 'maybe a little bit but I don't think it's enough to stop the ions'. If the latter, then please show me your calculations, or argue with mine, as 0.05T is not much of a field next to coils pumping out 1T.

You may have been told that the ions are heavy enough to go in a straight line, I am simply asking to go through the calculation to be clear whether that is a true statement or not.

[Art Carlson]

This doesn't make sense. Reaction force as in Newton's third law and rockets?

Really, and, pray tell, how much of the vacuum vessel would the plasma fill if the divertor was not there??

Your answer should then be 'up to the wall', or whatever other physical structure gets in the way of the plasma first.

If it was 'magnetically confined' then it would/could be the magnets alone that could hold in a plasma from escaping beyond a specific volume. But this doesn't happen. You could call it 'magnetic/divertor' confinement if you wish, but 'magnetic confinement' is well understood but potentially misleading as it suggests it confines like a bottle or a box does, yet - it doesn't.

'Confinement' is done by the thing which stops stuff going any further than some given point. At which point does the magnetic field in a tokamak, or in a Polywell, actually and properly stop it from migrating any further?

Nobody ever said magnetic confinement was perfect confinement. That's why there are concepts like "confinement time". But the divertor (or limiter) doesn't confine the plasma it sees. On the contrary, it sucks it up. In fact, it increases the cross-field diffusion by increasing the density gradient. (A divertor is a good idea nenetheless, but for other reasons.)

By your definition of confinement, the drain in my bathtub confines the water to one end because it stops it from getting to the other end. I suppose you can use the language that way, but it's not how the word is used in fusion research.

It might be helpful to distinguish between particle confinement time and configuration time (although the latter term is not used very often). A typical shot on ASDEX Upgrade maintains a plasma with very constant properties and geometry for about 5 seconds. The energy confinement time is maybe 0.1 sec, and the particle confinement time a few times longer. The opposite case is also possible, that a configuration disrupts before very many particles have been lost.

I feel yours is a slightly ad hominem comment ...

You're right. I'm getting tired. Sorry.

[chrismb]

And you are right that it is 'just a definition'.

Merriam webster:

'Confine':
1 a: to hold within a location b: imprison
2: to keep within limits

But the divertor (or limiter) doesn't confine the plasma it sees.

Why is it called the 'limiter'? - perhaps because it limits?? This *IS* the definition of 'to confine.

It may be that tokamak scientists are using a different definition of 'to confine' than is the dictionary definition, but that's not really an issue up to me, except to point out that it is disingenuous to non-toakamak folks.

Water in a bath tub is 'held in its location' by a) gravity, which is opposed by b) a normal reaction to the bath tub, c) a normal reaction to the plug. It is, therefore, not strictly 'gravitationally confined' because you need some equipment around it. The Moon and other satellites are exaples of pure gravitational confinement, but bath water isn't.

This is a distraction to the Polywell discussion, though. Concave or convex, a magnetic surface (and nothing else) will let charged particles migrate through it like ball-bearings through treacle until they reach the bottom of the tin (or in Polywell's case, the remaining chamber/coil structures). There is no hard force stopping them. Whether that is a Polywell magnetic surface, or a tokamak magnetic surface. I do not see how this is a point of dispute?

[chrismb]

I have just had a look on USPTO system to see where the last Polywell patent has got to. (20080187086)

I note that the examiner, Vadim Dudnikov, also appears to have decided that there is something screwy about trying to claim the Polywell as both a magnetic confinement device and a collisional device. As I read it, he's requested that the applicant decide whether it is a magnetic confinement device or an ion-collisional device, because it doesn't make sense to claim it as both.

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