Is There an Optimal Size for Magrid Casings?

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

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KitemanSA
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Postby KitemanSA » Mon Feb 16, 2009 2:43 am

Billy Catringer wrote:The trouble we are confronted with is that we have have some structural requirements that must be met. The SC cores are going to be dangerously brittle at LHe temperatures. The reason I am talking about tire-like shapes is to insure that the stresses placed on the cores can always be evenly distributed in compression. Any other form of stress, including tension, will likely cause fractures in the SC cores.

Which is why I DON'T think a standard circular plan form will do at all. The radial forces from the virtual coil is sure to mess up your stesses. I think we already got a demonstration of that with WB-6.

Billy Catringer
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Postby Billy Catringer » Mon Feb 16, 2009 2:55 am

KitemanSA wrote:Which is why I DON'T think a standard circular plan form will do at all. The radial forces from the virtual coil is sure to mess up your stesses. I think we already got a demonstration of that with WB-6.


Hmm, let me offer you a proposal. We are a long way from building anything. Lemme draw this thing and then let's run some finite element analysis on it to see what happens. Said analysis should tell us what changes need to be made fairly quickly. Getting a start is the important thing and drawings are a lot easier to change than copper and stainless. We haven't bought any copper or stainless yet and won't be for a while.
Last edited by Billy Catringer on Mon Feb 16, 2009 2:57 am, edited 1 time in total.

MSimon
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Postby MSimon » Mon Feb 16, 2009 2:56 am

KitemanSA wrote:
Billy Catringer wrote:The trouble we are confronted with is that we have have some structural requirements that must be met. The SC cores are going to be dangerously brittle at LHe temperatures. The reason I am talking about tire-like shapes is to insure that the stresses placed on the cores can always be evenly distributed in compression. Any other form of stress, including tension, will likely cause fractures in the SC cores.

Which is why I DON'T think a standard circular plan form will do at all. The radial forces from the virtual coil is sure to mess up your stesses. I think we already got a demonstration of that with WB-6.


WB-6 failed due to movement of the coil windings during pulses abrading the insulation of the coils leading to a catastrophic defect. I don't think it proves anything about the forces involved except that if poorly accounted for there will be trouble.
Engineering is the art of making what you want from what you can get at a profit.
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Billy Catringer
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Postby Billy Catringer » Mon Feb 16, 2009 3:44 am

tombo wrote:A few thoughts:

Hanging the cube from one corner makes the buckling forces on the supports smaller.
This may allow us to reduce cross sections.
It also simplifies the design by making all the coils structurally equivalent.
See page 14 of this for a picture.


I am taking a very hard look at this one. It may well solve my plumbing nightmare. Mind you, I am having real nightmares about the plumbing.

tombo wrote:Welcome Billy!


Thank you very kindly, Tombo.

tombo wrote:The tension on the SC is dependent on the relative thermal expansion coefficients of the SC wire vs its support (and of course between all the other layers too).


This is something we will need to run by the SC magnet guys the first chance we get. I am thinking it would be best to make supports out of flourinated ethylene propylene to bed the cores inside their supporting tubes.

tombo wrote:The mechanical loads from the B fields are directly on the SC itself.
The technique of transferring that load across several layers of vacuum to ground it to the strength members is pretty sketchy as is the fabrication process.


I am working on both at the moment. I have no doubt that much of it will have to be changed during the course of our little study, but as I pointed out elsewhere in this thread, designing these monstrous magnets will necessarily be an iterative process.

tombo wrote:A reason for hot water (rather than supercritical steam or NaK) outer coolant is the larger delta T across a given thickness of the outer tube(shell) moves more heat across the outer shell from the fixed max temperature of the outer surface <1000C absolute max for Cu to the coolant.
Not only that but, more pressure from supercritical h2o requires thicker copper shell which in turn reduces the heat flow.
This also causes 4 cm thick outer shell to be a no-can-do. Therefore the structural layer will have to be an inner one, preferably one at a reasonable temperature, not too cold, not too hot.


Run this one by Chief Simon. Both you and he say that a thick outer shell is problematical, and I dislike running a support all the way to the tubing with LHe inside. I consider myself outvoted on the outer shell thickness by better minds. Right now, I am thinking of a thick shell on the Cool Water tube.

tombo wrote:Heat flow and therefore current flow is complicated by the fact that almost all of the heat is deposited on one half of the circumference. My thought has always been to guide the water into a spiral path by wrapping a spring around the inner tube before bending the tubes to shape. This is the classic tool to keep tubes from kinking during bending too.


I think the MSimon and I have this one covered.

tombo wrote:When planning coolant paths we need to be aware of the need for the removal of bubbles entrained in the coolants. (especially if they are being operated near their boiling points)
That is a point toward using supercritical pressures.


I don't know if a standard deaerater will do for these monsters or not. Your point is well taken, though.

tombo wrote:If you take the above pictured coils and reconnect the corners you can make it in one pass. Like this...BIG SNIP... radial direction.


Conceivably, this would eliminate my nightmares about the plumbing, but will the water jackets remove enough heat before the SC coils get warmed up? Speaking of coils, how could this thing be wound? With this shape of Magrid, we are going to be talking about a form of Bitter Plate.

tombo wrote:Yes, anything other than a simple torus complicates the field calculations, but whether the effect on performance is positive or negative is unknown.


Again, I'll offer you the same proposal I offered KitesmanSA. Lemme draw what I know and THEN let's analyze it to see what happens. The idea is to get something started. The fun is just beginning.

Billy Catringer
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Postby Billy Catringer » Mon Feb 16, 2009 3:48 am

To everyone.

I found this little series to be informative about difficult projects, including a few delectable hints about insulating cryogenic systems.

http://www.youtube.com/watch?v=SQO3Uf35beQ

MSimon
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Postby MSimon » Mon Feb 16, 2009 4:54 am

Right now, I am thinking of a thick shell on the Cool Water tube.


That could work. It will also support higher stresses than a hot water (if it is hot enough) shell could. No temperature derating - for brittleness on the cold side or lack of material strength on the hot side.
Engineering is the art of making what you want from what you can get at a profit.
http://protonboron.com/
THE OPEN POLYWELL FUSION CONSORTIUM

Billy Catringer
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Postby Billy Catringer » Mon Feb 16, 2009 5:00 am

:D

MSimon
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Postby MSimon » Mon Feb 16, 2009 6:20 am

Billy Catringer wrote:To everyone.

I found this little series to be informative about difficult projects, including a few delectable hints about insulating cryogenic systems.

http://www.youtube.com/watch?v=SQO3Uf35beQ


Blogged it:

http://powerandcontrol.blogspot.com/200 ... rs-do.html

Thanks!
Engineering is the art of making what you want from what you can get at a profit.
http://protonboron.com/
THE OPEN POLYWELL FUSION CONSORTIUM

Aero
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Postby Aero » Sat Feb 21, 2009 10:32 pm

Its probably been considered before but if so, I missed it.

Have we considered that first (Outer) water jacket need not enclose the complete coil, but only shield the Magrid from the fusion products of the core? That is, it could be a half jacket if a way could be found to support it. Such an arrangement should make the plumbing problem to the inner cooling jackets a little more tractable.
Aero

Billy Catringer
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Postby Billy Catringer » Sat Feb 21, 2009 10:40 pm

Aero wrote:Its probably been considered before but if so, I missed it.

Have we considered that first (Outer) water jacket need not enclose the complete coil, but only shield the Magrid from the fusion products of the core? That is, it could be a half jacket if a way could be found to support it. Such an arrangement should make the plumbing problem to the inner cooling jackets a little more tractable.


I'll hafta think about this one, Aero. I was in the middle of teaching myself to use Blender when some paying work came along. Gotta take care of the paying work first.

tombo
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Postby tombo » Sun Feb 22, 2009 10:53 pm

YES. This is almost perfect except the sides should be aligned a bit more
They are aligned exactly on the cube edges. It is hard to tell unless you are looking exactly along the plane. But that view does not show the overall shape well.

Please bow them, but not make them circular.
Yes that was what I was trying to describe. Words are so hard to use when describing geometry. (I have not yet because that shape is harder to draw.)

I think it will improve the funny cusp performance.
I've heard that before. But why? or maybe more to the point, how?

Also, if we can place thin tensile members across the vertexes connecting the circular arc segments then most of the forces resolve to simple hoop stresses.
The problem of course is the plasma. But, I think that is the lowest plasma density highest B field region in the whole sphere.

funkiest looking tire I've ever seen
Yes, I was just picking up the term as a zeroth order approximation to set the scene before getting on to what I really wanted to say.

I am trying to stuff too many ideas into these little messages.
Yes, Its exciting isn't it. [help help I've fallen and I can't shut up. :lol: :roll:]

I am having real nightmares about the plumbing.
Yes, those piping nightmares are what got me started along the line of thought that lead to that picture.

WB-6 failed due to movement of the coil windings during pulses abrading the insulation of the coils leading to a catastrophic defect.
All the more reason to think hard and early about the stresses on those SC's.

I recall some of the mfr's options included internal coolant passages.
If a ring of coolant passages were embedded in the outside layer of the SC assembly at the factory it would make the SC a structurally tractable component.

Lemme draw what I know and THEN...
Awww come on why do you want to hog all the fun?

transferring that load across several layers of vacuum
Some thoughts here (caveat I have little cryogenic experience), but:
I have seen LN2 sit overnight in a Styrofoam coffee cup with some but not a lot of evaporation. I have seen it stored for months in an insulated barrel that again looked a lot like a Styrofoam picnic jug. It sure did not look like a Dewar.
Coffee cup is what maybe 1/8" thick.
That tells me we can use Styrofoam or similar stronger plastic as the insulator between the cold water (300K) and the LN2(77K). Delta Temp = 223K
From LN2(77k) to LH2(20K) Delta Temp = is only 57K.
That tells me we can use the same stuff. Or a cold adapted version.
Viola, no vacuum gaps with their compressive, tensile and shear strengths of precisely zero.
Expanding foam insulation injected between tubes to pre-compress itself as it cures in situ looks mighty inviting.

Speaking of coils, how could this thing be wound?
My first choice is 1 turn with the last transformer really close.
If not possible then it would need splices to connect multiple wires running through the device in series. But that gets ugly when you start looking at the B fields in the junction box. Gotta watch those sharp high current turns. I've seen them sap power and cause collateral damage.

It MIGHT be possible to assemble the nested piping/wiring in a straight configuration, then bend it to the desired polyhedron.
The biggest tasks there are:
Keeping the layers concentric. (coiled spacers)
Avoiding buckling. (coiled spacers)
Keeping the SC from being stretched in the process. (loose enough fit.)

The shape I drew would be easy to fabricate for the LN2 cooled copper tubing version for sizes up to a meter in diameter. I have worked with tubing fitters who could knock that one out in say 25 bends times 10 minutes per bend is a little over 4 hours. 1 minute per bend in 1/2" copper tubing gives half an hour for the 3rd one.

That still leaves a lot of work to do:
Thread it through the electrical insulator.
Braze on the thru-wall vacuum fittings and the tensile ties.
Connecting all the layers to the infrastructure is still a problem to be solved.
But, at least it is done outside the chamber, and I think not too bad given enough elbow room.
Unless you want to try to make all those SC electrical cross-connects right at the Magrid itself and also to rejigger the coolants to keep the SC covered properly all without making a bulge.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

MSimon
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Postby MSimon » Mon Feb 23, 2009 12:34 am

Expanding foam insulation injected between tubes to pre-compress itself as it cures in situ looks mighty inviting.


It has to withstand a high radiation environment (even with pB11).

And yeah. Construction of concentric bent tubes is a bitch. I assume the MRI guys have figured it out and we can build on that.
Engineering is the art of making what you want from what you can get at a profit.
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tombo
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Postby tombo » Mon Feb 23, 2009 2:11 am

MSimon wrote:We can start out with a 10 Tesla coil 2 meters in dia. 16 million ampere turns.

Using Indrek's equation at http://www.mare.ee/indrek/ephi/force/
I get 650 million Newtons or 146 million pounds!?!
Ouch!
Is that right?
That would take a solid cylinder of 36 ksi garden variety structural steel 72" =1.83 meters diameter to hold.
That is almost as big as the coil itself.
Please somebody show me where I’m being stupid this time.
-Tom Boydston-

"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

Billy Catringer
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Postby Billy Catringer » Mon Feb 23, 2009 3:06 am

tombo wrote:
MSimon wrote:We can start out with a 10 Tesla coil 2 meters in dia. 16 million ampere turns.

Using Indrek's equation at http://www.mare.ee/indrek/ephi/force/
I get 650 million Newtons or 146 million pounds!?!
Ouch!
Is that right?
That would take a solid cylinder of 36 ksi garden variety structural steel 72" =1.83 meters diameter to hold.
That is almost as big as the coil itself.
Please somebody show me where I’m being stupid this time.


Well, if you are right, we are going to need a ton or two of miraculium for the cool water jackets.

MSimon
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Postby MSimon » Mon Feb 23, 2009 3:23 am

tombo wrote:
MSimon wrote:We can start out with a 10 Tesla coil 2 meters in dia. 16 million ampere turns.

Using Indrek's equation at http://www.mare.ee/indrek/ephi/force/
I get 650 million Newtons or 146 million pounds!?!
Ouch!
Is that right?
That would take a solid cylinder of 36 ksi garden variety structural steel 72" =1.83 meters diameter to hold.
That is almost as big as the coil itself.
Please somebody show me where I’m being stupid this time.


MRI coils at 1 T don't seem to generate these kinds of forces.
Engineering is the art of making what you want from what you can get at a profit.
http://protonboron.com/
THE OPEN POLYWELL FUSION CONSORTIUM


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