A question about higher order polyhedra.

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

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MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote:
Bigger fields mean bigger, heavier magnets, and sometimes space and weight is important.
Not if you lower the SC coil operating temps.

Space is less important than it is at lower field strength since above around .35 T ions no longer impinge on the coils. Operating at 3 T or above ought to allow you a larger projected area fraction than the original 20% contemplated.
Please, apples to apples, one thing at a time! The question is, given a magnet condtion, is it better to improve the sphericity or to increase the strength. Until we know what the improvement is, and what the actual need is, we can't just assume that we can just make the system with stronger magnets and be ok.
FWIW we have Doc B's estimate of a 3X to 5X improvement.
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MSimon
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Post by MSimon »

True, there is a face opposite each and every face of an octa. But with an UNtruncated octa polywell, the magnet on one face will be the opposite polatity of the one on the opposite face. If one is North in, the other will be North out. They don't become "opposed fileds" (both N-in) until you use the rectified octa.
Why? If all the faces have N facing in (as in the cube) I don't see what you propose as intrinsic. True the current in the magnet will be going in opposite directions on opposite faces, but that is also true of the cube.
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 »

Eventually, it is just not practical to ASSUME we can improve the field strength.
Actually I have looked at SC magnets and you can improve the Jc significantly by lowering the coil temps.

In any case we know from work already done that 20T can be done with coils of approximately similar size. An increase from 10 T to 20 T improves confinement (loss reduction) by a factor of 16. And that is with 4K coils. If it is worth while re: costs, higher fields at lower temps are probably in the cards.

As I said theoretically 100 T at 0K has been measured. (might have been extrapolated so it is not certain) But that is with current materials. Who knows what the next breakthrough will be?

I have seen Jc graphs of some SCs that go up an order of magnitude with small changes in T around 4K. I'll look at some of my SC pdfs and get back to you.

I'm not going to say either way which is the best alternative. We won't know until experiments are done followed by engineering estimates.
Engineering is the art of making what you want from what you can get at a profit.

KitemanSA
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Post by KitemanSA »

MSimon wrote:
True, there is a face opposite each and every face of an octa. But with an UNtruncated octa polywell, the magnet on one face will be the opposite polatity of the one on the opposite face. If one is North in, the other will be North out. They don't become "opposed fileds" (both N-in) until you use the rectified octa.
Why? If all the faces have N facing in (as in the cube) I don't see what you propose as intrinsic. True the current in the magnet will be going in opposite directions on opposite faces, but that is also true of the cube.
Are you expecting there to be NO north out portion anywhere, a magnetic monopole? If so, good luck! If you try making all faces in with no truncation, you will get NO field at all. If you intend to have truncation, I've already agreed with you and proceeded to discussing the OTHER possibility with an octahedron, the one with NO truncation and alternate polarities around the faces.

KitemanSA
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Post by KitemanSA »

MSimon wrote:
Eventually, it is just not practical to ASSUME we can improve the field strength.
Actually I have looked at SC magnets and you can improve the Jc significantly by lowering the coil temps.
Apples to apples PLEASE. If you can get such an increase productively with the WB6 format, I can get it with the better sphericity, and we are back to BIGGER vs more spherical. APPLES TO APPLES PLEASE!!

KitemanSA
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Post by KitemanSA »

MSimon wrote: I'm not going to say either way which is the best alternative. We won't know until experiments are done followed by engineering estimates.
CONCUR!!! :!: :!: :!:

pfrit
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Post by pfrit »

MSimon wrote:In any case we know from work already done that 20T can be done with coils of approximately similar size. An increase from 10 T to 20 T improves confinement (loss reduction) by a factor of 16. And that is with 4K coils. If it is worth while re: costs, higher fields at lower temps are probably in the cards.

As I said theoretically 100 T at 0K has been measured. (might have been extrapolated so it is not certain) But that is with current materials. Who knows what the next breakthrough will be?

I have seen Jc graphs of some SCs that go up an order of magnitude with small changes in T around 4K. I'll look at some of my SC pdfs and get back to you.

I'm not going to say either way which is the best alternative. We won't know until experiments are done followed by engineering estimates.
The non-desctructive pulse magnets are currently at 90T, but should hit 100T this summer. It is beside the point, however. All of the magnets > 29T are hybrid magnets. That means that they have a bitter magnet core. A bitter magnet CANNOT have a large core. The core on these suckers are on the order of 2 cm. Can't makethem much bigger. You want a wound SC magnet. The cheap ones that the use in MRIs top out at 15T. Limits of the material. SC magnets that can take higher mag fields are very hard to wind. Like YBCO which is a ceramic. Really expensive and as far as I know, they are not formed with large cores. Don't count on a 20T SC magnet with a inner core diameter > 2m costing less than the statue of liberty (I really don't know how much it would cost but it would be big). Stick with MRI magnets. The wikipedia has a lot of good info on this.
What is the difference between ignorance and apathy? I don't know and I don't care.

MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote:
True, there is a face opposite each and every face of an octa. But with an UNtruncated octa polywell, the magnet on one face will be the opposite polatity of the one on the opposite face. If one is North in, the other will be North out. They don't become "opposed fileds" (both N-in) until you use the rectified octa.
Why? If all the faces have N facing in (as in the cube) I don't see what you propose as intrinsic. True the current in the magnet will be going in opposite directions on opposite faces, but that is also true of the cube.
Are you expecting there to be NO north out portion anywhere, a magnetic monopole? If so, good luck! If you try making all faces in with no truncation, you will get NO field at all. If you intend to have truncation, I've already agreed with you and proceeded to discussing the OTHER possibility with an octahedron, the one with NO truncation and alternate polarities around the faces.
No. I expect that the S poles will be squeezed between the magnets. Just as it is in the cube design. Which is one of the reasons for the spacing between the coils.
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MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote:
Eventually, it is just not practical to ASSUME we can improve the field strength.
Actually I have looked at SC magnets and you can improve the Jc significantly by lowering the coil temps.
Apples to apples PLEASE. If you can get such an increase productively with the WB6 format, I can get it with the better sphericity, and we are back to BIGGER vs more spherical. APPLES TO APPLES PLEASE!!
It is just a matter of cost. If more cooling is more cost effective than more coils then more cooling and higher fields is the way to go.

If bigger magnets are more cost effective than more magnets then that is the way to go.

I'm not looking at it as a physics problem. I'm looking at it as an engineering problem. Dollars to dollars.

Engineering is the art of making what you want from what you can get at a profit.
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 »

pfrit wrote:
MSimon wrote:In any case we know from work already done that 20T can be done with coils of approximately similar size. An increase from 10 T to 20 T improves confinement (loss reduction) by a factor of 16. And that is with 4K coils. If it is worth while re: costs, higher fields at lower temps are probably in the cards.

As I said theoretically 100 T at 0K has been measured. (might have been extrapolated so it is not certain) But that is with current materials. Who knows what the next breakthrough will be?

I have seen Jc graphs of some SCs that go up an order of magnitude with small changes in T around 4K. I'll look at some of my SC pdfs and get back to you.

I'm not going to say either way which is the best alternative. We won't know until experiments are done followed by engineering estimates.
The non-desctructive pulse magnets are currently at 90T, but should hit 100T this summer. It is beside the point, however. All of the magnets > 29T are hybrid magnets. That means that they have a bitter magnet core. A bitter magnet CANNOT have a large core. The core on these suckers are on the order of 2 cm. Can't makethem much bigger. You want a wound SC magnet. The cheap ones that the use in MRIs top out at 15T. Limits of the material. SC magnets that can take higher mag fields are very hard to wind. Like YBCO which is a ceramic. Really expensive and as far as I know, they are not formed with large cores. Don't count on a 20T SC magnet with a inner core diameter > 2m costing less than the statue of liberty (I really don't know how much it would cost but it would be big). Stick with MRI magnets. The wikipedia has a lot of good info on this.
Here is a better one:

http://www.hep.ucl.ac.uk/undergrad-proj ... e/cool.htm

It is about the LHC.

Here are the ITER magnets:

http://magnets-industry-workshop.web.ce ... ortone.pdf

I was mistaken. The top field for large bore physics experiments is not 20 T it is around 12 T.
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KitemanSA
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Post by KitemanSA »

MSimon wrote: It is just a matter of cost.{Emphasis Added}
No, it isn't; at least not always. Some times it is a matter of space and weight too. And when it is just cost, data is key to getting best cost. We need the data. Then we can tell how to engineer this thing rather than just design it.

MSimon
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Post by MSimon »

KitemanSA wrote:
MSimon wrote: It is just a matter of cost.{Emphasis Added}
No, it isn't; at least not always. Some times it is a matter of space and weight too. And when it is just cost, data is key to getting best cost. We need the data. Then we can tell how to engineer this thing rather than just design it.
I was thinking of terrestrial applications. Once you go mobile (ships, rockets) space and weight considerations become more important.
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Aero
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Post by Aero »

Once you go mobile (ships, rockets) space and weight considerations become more important.
That brings up a question. How much energy does it take to accelerate a 1 Kg mass at 1 g? Assume perfect conversion to kinetic energy, for the moment.
The question is rooted in the fact that it takes 143 years to accelerate a 100 metric ton spacecraft to 1% c, if it only has a 100 Mw power plant, and perfect conversion. I want to launch from Earth's surface, what size BFR do I need?
Aero

MSimon
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Post by MSimon »

Aero wrote:
Once you go mobile (ships, rockets) space and weight considerations become more important.
That brings up a question. How much energy does it take to accelerate a 1 Kg mass at 1 g? Assume perfect conversion to kinetic energy, for the moment.
The question is rooted in the fact that it takes 143 years to accelerate a 100 metric ton spacecraft to 1% c, if it only has a 100 Mw power plant, and perfect conversion. I want to launch from Earth's surface, what size BFR do I need?
Actually you need two different types of rocket for that application. One a high thrust device to get to LEO with moderate ISP and another lower thrust device wit high ISP.

But let us see if we can work it out:

F=ma and E=Fs and s = 1/2 at^2 and P= E/t

F = force
m = mass
a = acceleration
E = energy
s = distance
t = time
P = power

That should cover the light speed device provided the fuel mass is a small fraction (on the order of a few % or less) of rocket mass.

For the boost to LEO it is a bit more complicated due to the fact that the reaction mass is a significant fraction of the total mass. So the force is constant while the mass is decreasing.

And then there is the reqmt (for humans) of keeping the acceleration constant. So the mass flow rate would be continually decreasing during ascent.
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Aero
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Post by Aero »

I didn't want to get that complicated. The 143 years to 1% c comes from assuming 100% efficiency in converting reactor power to kinetic energy. Conservation of energy prohibits anything more efficient. Of course there are a lot of things (everything?) that are less efficient.
Aero

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