STATEMENT OF OBJECTIVES from RFP

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

Moderators: tonybarry, MSimon

ekribbs
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Post by ekribbs »

KitemanSA wrote:A balloon doesn't need a "cage" to hold it in. The pressure loads the material with simple membrane stresses.

A polywell doesn't need a cage either. Given a layup like being discussed in the design topic, the repulsive forces can be taken out with simple tensile loads in the coil backbone. No cage needed. This rather light structure can be suspended with the four radial i/o leads.
You missed the theme of this discussion. We were concerned with the electron losses at the "nubs" that hold the magnet coils together, which as everyone agreed were in tension due to the radially outward magnetic forces.

Tom Ligon and I suggested removing the "nubs" to really eliminate the electron losses. Consequently, there would be nothing to hold the magnets together in the current arrangement of WB-6/7. We suggested that for a future re-design, an insulated pipe truss attached to the inner pressure vessel walls could be employed to support each magnet separately. MSimon wants to build an inner structural cage instead of going directly to the pressure walls to shorten the length of the truss/towers. I suggested a radial configuration of the magnets with two co-linear magnets on the central "axis" to close out the magnetic bottle to be more conformal to a cylindrical pressure vessel.

KitemanSA
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Post by KitemanSA »

ekribbs wrote:You missed the theme of this discussion. We were concerned with the electron losses at the "nubs" that hold the magnet coils together, which as everyone agreed were in tension due to the radially outward magnetic forces.

Tom Ligon and I suggested removing the "nubs" to really eliminate the electron losses. Consequently, there would be nothing to hold the magnets together in the current arrangement of WB-6/7. We suggested that for a future re-design, an insulated pipe truss attached to the inner pressure vessel walls could be employed to support each magnet separately. MSimon wants to build an inner structural cage instead of going directly to the pressure walls to shorten the length of the truss/towers.
And I followed that discussion with the fact that the layup discussed in the other thread obviates the entire issue.
The nubs are only a problem where they are. Most folks argee they need to be moved. Replacing them with additional magnetically protected crossovers away from the funny cusp eliminates that problem.
As to the odd torques and moments introduced with the radial supports and cages, all obviated with the proper layup.

Billy Catringer
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Post by Billy Catringer »

ekribbs wrote: You missed the theme of this discussion. We were concerned with the electron losses at the "nubs" that hold the magnet coils together, which as everyone agreed were in tension due to the radially outward magnetic forces.

Tom Ligon and I suggested removing the "nubs" to really eliminate the electron losses. Consequently, there would be nothing to hold the magnets together in the current arrangement of WB-6/7. We suggested that for a future re-design, an insulated pipe truss attached to the inner pressure vessel walls could be employed to support each magnet separately. MSimon wants to build an inner structural cage instead of going directly to the pressure walls to shorten the length of the truss/towers. I suggested a radial configuration of the magnets with two co-linear magnets on the central "axis" to close out the magnetic bottle to be more conformal to a cylindrical pressure vessel.

Can anyone tell us what the ID of the vessel needs to be to hold a magried made up of 2 meter coils or Bitter Plates? The pictures I have seen suggest that at least one magnet diameter between the magrid and the vessel walls is necessary. However, with magnets this size we are dealing with magnetic fields that are much stronger than those developed by WB6.

The sizes and weights of the structures are dictated by the room required by the physics. Welding the support structures to the vessel walls is attractive because the atmosphere outside the vessel is helping to hold things together. If necessary we can do all kinds of things on the outside to stiffen the vessel walls, but it is hard to get an idea of what any of the structure needs to be without knowing how much circulation room the particles need.

KitemanSA
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Post by KitemanSA »

Folks, the only forces the vacuum chamber walls need to see are from atmospheric pressure and the weight of the MaGrid. The magnetic forces should all be taken up in the structure, the backbone, of the MaGrid.

Art Carlson
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Post by Art Carlson »

KitemanSA wrote:The nubs are only a problem where they are. Most folks argee they need to be moved. Replacing them with additional magnetically protected crossovers away from the funny cusp eliminates that problem.
They've got to be someplace in the gaps between coils, and the line cusps run through all the gaps. And magnetic protection will not eliminate the problem in this topology, just shift it to a different place.

Art Carlson
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Re: Asymmetry causes vorticity?

Post by Art Carlson »

icarus wrote:I think this thing is gonna want to spin up and rather quickly.
If you can apply a steady torque to a plasma with time-invariant magnetic fields, then you've got a nifty perpetual motion machine.

Billy Catringer
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Re: Asymmetry causes vorticity?

Post by Billy Catringer »

Art Carlson wrote:
icarus wrote:I think this thing is gonna want to spin up and rather quickly.
If you can apply a steady torque to a plasma with time-invariant magnetic fields, then you've got a nifty perpetual motion machine.

Art, I know you think that this beast hasn't a prayer of ever working. I am even willing to say that hte odds are in your favor. Let's put that aside for a moment. Can you tell me what the minimum amount of room is needed around 2 meter coils producing 10T fields if the bloody thing is to have the remotest chance of working? This really is a vitally important question.

KitemanSA
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Post by KitemanSA »

Art Carlson wrote: They've got to be someplace in the gaps between coils, and the line cusps run through all the gaps. And magnetic protection will not eliminate the problem in this topology, just shift it to a different place.
Unless you have coils between the coils, just not at the apex of the funny cusp.

I have been nuudging tombo into drawing up what I think this thing needs to look like. It is a slight modification of what DrB seemed to have in mind. In the end, there will be two pair of coils surrounding each funny cusp, and the quasi-line cusp will be history.

TallDave
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Post by TallDave »

If you can apply a steady torque to a plasma with time-invariant magnetic fields, then you've got a nifty perpetual motion machine.
Heh. But have we ruled out the possibility we're gaining energy from electrons falling to fractional states?
I suggested a radial configuration of the magnets with two co-linear magnets on the central "axis" to close out the magnetic bottle to be more conformal to a cylindrical pressure vessel.
I'm having trouble picturing this. It sounds very un-WB, though.

ekribbs
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Post by ekribbs »

Billy Catringer wrote:
ekribbs wrote: You missed the theme of this discussion. We were concerned with the electron losses at the "nubs" that hold the magnet coils together, which as everyone agreed were in tension due to the radially outward magnetic forces.

Tom Ligon and I suggested removing the "nubs" to really eliminate the electron losses. Consequently, there would be nothing to hold the magnets together in the current arrangement of WB-6/7. We suggested that for a future re-design, an insulated pipe truss attached to the inner pressure vessel walls could be employed to support each magnet separately. MSimon wants to build an inner structural cage instead of going directly to the pressure walls to shorten the length of the truss/towers. I suggested a radial configuration of the magnets with two co-linear magnets on the central "axis" to close out the magnetic bottle to be more conformal to a cylindrical pressure vessel.

Can anyone tell us what the ID of the vessel needs to be to hold a magried made up of 2 meter coils or Bitter Plates? The pictures I have seen suggest that at least one magnet diameter between the magrid and the vessel walls is necessary. However, with magnets this size we are dealing with magnetic fields that are much stronger than those developed by WB6.

The sizes and weights of the structures are dictated by the room required by the physics. Welding the support structures to the vessel walls is attractive because the atmosphere outside the vessel is helping to hold things together. If necessary we can do all kinds of things on the outside to stiffen the vessel walls, but it is hard to get an idea of what any of the structure needs to be without knowing how much circulation room the particles need.
The Navy is your customer. The Navy probably wants a better power unit for their submarines. If the result is as big as a house and will only fit into an aircraft carrier, they will probably choke on your design.

If someone adopted my "6 cylinder" approach described previously, a 2 meter diameter magnet would have a roughly 4 meter overall magrid diameter. Add another 2 meters between the magrid and the and the pressure vessel, and you have an 8 meter diameter pressure vessel. 8 meters. 26 feet. big as a small house

But guys,you are forgetting the wonderful scaling law discovered by Dr. Bussard. (B^^3)*R !!

Stop trying to make it bigger, and concentrate on boosting the B field and get cubed improvement instead of boosting R and getting linear improvement. With the current
70cm magnet diameter, the same "6 cylinder" design would have only a roughly 1.5 meter magrid diameter. Add .75 meter to the radius of that for the pressure vessel, and you get a nice 3 meter diameter pressure vessel. Stack radial layers as I suggested before, and you get a long salami 3 meters in diameter that fits nicely in a submarine.

The Navy loves things that are easy to maintain. Make the pressure vessel very stout and give it portholes corresponding to the radial and longitudinal position of each magnet.
Make modular magnet/truss/backplate assemblies as I suggested before. The truss in this case would only be 70cm tall. Nice and short and resistant to bending. Make the backplate so it fits into a modular pressure porthole on the pressure vessel. Make the pressure vessel, (after removing all external power, cooling, whatever, fittings, etc.) Rotate-able on rollers inside the submarine. In dry-dock, a hatch is opened above the engine. The pressure vessel external fittings are removed. The pressure vessel is rotated so that a failing magnet/truss module is exposed on top. Swabbies unbolt the module backplate from the pressure vessel and lift the module straight up and out.

The Navy will love you to death.

If you build a monolythic thing like WB-6/7 where all magnets are wired and cooling-piped and welded together into one big Gordian knot, the Navy is not going to be impressed much.

On the issue of space for electron/ion re-circulation between the magrid and the pressure vessel, a whole lot of space probably is not needed. More important is that the outer negatively charged grid be as symmetrical as possible to the magrid for even flow.

Billy Catringer
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Post by Billy Catringer »

I do not doubt that the Navy wants this thing to power its new ships. In fact, the Navy would likely be thrilled beyond words if it could be retrofitted into some of their existing hulls, the Virginia Class subs leap to mind immediately. Were I an admiral at BuShips, I would want it for my next class of boomers. No arguments on this point from me.

However, we did not build our first fully functioning reactor for a submarine. We are here talking about the next step up from WB7.x. I do not doubt that what you are suggesting or something very much like it will eventually be built. Assuming the physics works, a very large unknown at the moment, engineering and construction needs to move along at a rapid pace. This thing is needed all over the country.

We need a design that we can be build at reasonable cost in a hurry knowing that the chances of said design will work are quite high. We can improve gain and make it smaller later.

KitemanSA
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Post by KitemanSA »

I am under the impression that the distance between the MaGrid and the shell is dictated by two factors, the drive voltage, and the density of neutrals. These two factors are somehow related to whether the MaGrid will arc to the shell. No?

TallDave
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Post by TallDave »

But guys,you are forgetting the wonderful scaling law discovered by Dr. Bussard. (B^^3)*R !! Stop trying to make it bigger, and concentrate on boosting the B field and get cubed improvement instead of boosting R and getting linear improvement.
It's actually B^4*R^3. An increase in B roughly squares the ability to trap electrons, which trap ions in roughly quasineutral fashion, and ion density squared is roughly the fusion power. Power also scales as radius cubed because that's the volume.

M Simon has calculated B improvements will likely be somewhat limited by the ability of Magrid materials to withstand the fusion energy (iirc state of the art is something like 1 MW/cm^2). In fact, over 100MW we may only see r^2 improvements in power (i.e., we'd be decreasing B at larger sizes because r^3 scales too fast) because the limiting factor will be the inverse square law.

Of course, too much power density will be a nice problem to have.

KitemanSA
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Post by KitemanSA »

TallDave wrote:
But guys,you are forgetting the wonderful scaling law discovered by Dr. Bussard. (B^^3)*R !! Stop trying to make it bigger, and concentrate on boosting the B field and get cubed improvement instead of boosting R and getting linear improvement.
It's actually B^4*R^3. An increase in B roughly squares the ability to trap electrons, which trap ions in roughly quasineutral fashion, and ion density squared is roughly the fusion power. Power also scales as radius cubed because that's the volume.
The power is B^4*R^3, GAIN is (I think) B^4*R but I've only ever seen it as R^5.

Skipjack
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Post by Skipjack »

The very first (working) nuclear reactor ever built was not fit to be put into a submarine either...
I would say: build something that works (no matter what) first, then think about making it fit into a sub or whatever.
If it is worth it, one can always build the submarine arround the reactor.
The germans had a lot of success with their small uboats (HDW 206 to 214). They usually build the rest arround the essentials. E.g. the new HDW type 212 clearly shows that it was designed to best fit the fuel cell power supply and electric engines. It is an excellent design and probably the most silent boat out there.
Anyway, I say make the dang Polywell reactor work first. Then think about the applications.

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