Talk-Polywell.org

KeithChard wrote:Elinvar is yet another possible first wall material of watchmaking origin.

The metal selected for the LHe wall should probably have the same thermal effects as the base tape metal from the superconductor. Otherwise, what started out as a good packing job could get either very tight of very loose. For the higher strength HTSCs that is usually stainless steel. Otherwise, copper alloys are often used to stabilize the HTSC. Use of fancy low thermal effect materials may be contra-indicated.

KitemanSA,

I was referring to the casing of the high temperature water circuit which will have to function in the full heat of the sun. Billy has already identified thermal expansion as a problem because of the temperature difference between the front facing side of the toroid and the rear, which will lead to distortion of the whole toroid and also compressive buckling of the hot face.

Sorry,
Confused your "first wall" with the innermost wall being discussed in the rest of the thread.

If he keeps going the way he is, he may need such esoteric materials. If he decouples the TPS from the core, I doubt thermal issues will be a big problem. (JMHO)

We'll see.

There is a problem with lack of readily available high temperature data on some of the materials I have suggested for the first wall.

It also appears that above the Curie temperature the thermal expansion coefficient ceases to be very low, and below this temperature the materials are ferromagnetic. We need paramagnetism and low thermal expansion simultaneously.

I think we need to search for a different class of materials. Perhaps there is a suitable bronze, as I suggested in an earlier post, but I am concerned that the outer surface temperature (under the 11B coating) may be too high for any material with a substantial copper content. However, the high thermal conductivity of the bronzes is a very favourable property.

On a different aspect of the Magrid design, has anyone considered the effects of the much larger separation between the magnets, enforced by the cooling system, on the power output and power losses of this reactor?

Edit: I think it will be best to start a thread on the Theory forum for this
last item.

KeithChard wrote:I think we need to search for a different class of materials. Perhaps there is a suitable bronze, as I suggested in an earlier post, but I am concerned that the outer surface temperature (under the 11B coating) may be too high for any material with a substantial copper content.

I've been mentally planning on one of the Hastelloy alloys. It has been successfully used in high temperature, high radiation fields for about half a century so I don't yet see the need to go to something else, except I don't know if it is ferromagnetic. Data anyone?

KitemanSA wrote:

KeithChard wrote:I think we need to search for a different class of materials. Perhaps there is a suitable bronze, as I suggested in an earlier post, but I am concerned that the outer surface temperature (under the 11B coating) may be too high for any material with a substantial copper content.

I've been mentally planning on one of the Hastelloy alloys. It has been successfully used in high temperature, high radiation fields for about half a century so I don't yet see the need to go to something else, except I don't know if it is ferromagnetic. Data anyone?

Good stuff. Very tough. Hard to work though.

One thing to keep in mind is that the temperature of the outer circuit is strictly a function of the size and design of the heat transfer eqpt. There is no steam plant. So we do not need high temps. The outer circuit can be run at what ever temperature makes sense. At least for test reactors.

I have a very tentative idea for the first wall mateial.

A two layer material consisting of one of the Inconel alloys for the outer layer and pure copper for the inner layer. The outer layer to be in tension by bonding the layers with the Inconel at high temperature and the bonding process to be explosive using a technique based on this:-
http://www.springerlink.com/content/r60r57uq11386088/

It is somewhat way out but it could solve an otherwise intractable problem of thermal buckling. Probably would require a lot of development, but this problem may do that anyway.

It appears that developments on the theory forum (Maximum size allowed...) mean that there may not be a significant first wall problem, which, from an engineering point of view, would be a great relief.

Billy: You may find that your favoured structural shell becomes the first wall, as a high temperature water jacket may not be needed.

KeithChard wrote:It appears that developments on the theory forum (Maximum size allowed...) mean that there may not be a significant first wall problem, which, from an engineering point of view, would be a great relief.

Billy: You may find that your favoured structural shell becomes the first wall, as a high temperature water jacket may not be needed.

I don't think the high temp. water jacket is eliminate. The required mass flows are reduced considerably though.

Which brings us back to the original topic of this thread, the SC/LHe structure. While Billy's picture is, to quote MSimon, "WOW"; it seems way too heavy to me. Billy still seems to be carrying all the magnetic expansion loads out thru the casing, and that really isn't necessary. The TWP needs only to shield the core, not support it. It needn't even touch it beyond the inner wall, the LHe wall.

A lot of this work seems a beautiful waste of time. Oh well.

KitemanSA wrote:Which brings us back to the original topic of this thread, the SC/LHe structure. While Billy's picture is, to quote MSimon, "WOW"; it seems way too heavy to me. Billy still seems to be carrying all the magnetic expansion loads out thru the casing, and that really isn't necessary. The TWP needs only to shield the core, not support it. It needn't even touch it beyond the inner wall, the LHe wall.

A lot of this work seems a beautiful waste of time. Oh well.

I think this is based on the fact that extreme cold makes metals brittle so that the best points for force transfer are the warm parts of the coils.

MSimon wrote: I think this is based on the fact that extreme cold makes metals brittle so that the best points for force transfer are the warm parts of the coils.

Which makes me pause, because I have read in many locations that the kinds of stainless steel used for SC applications do NOT get brittle and lose only negligable strength. The SC manufacturers use stainless steel for their tapes to improve the strength. I suspect they know something this forum is missing. PLEASE don't assume brittleness not in evidence!

It sounds like some networking is in order to bring a couple of specialists into the forum's open source work

Betruger wrote:It sounds like some networking is in order to bring a couple of specialists into the forum's open source work

A Google search might suffice.

First, let me apologize for my long absence. I had some paying work come in and I had to concentrate on it. Second, for those who missed it, I am making jackets and supports of the SC core from 5083-O aluminum, now, not stainless. This grade of aluminum gains strength as the temperature drops and it contracts at the same rate as the SC coil. That is two very large advantages all by themselves, but even more important is the enormous reduction in weight. I propose to use that material for the LHe core, the first vacuum jacket, the LN2 jacket and the 2nd vacuum jacket.

I propose to make the cool water jacket out of Inconel 690. It is very high strength and has zero cobalt in it. It machines and welds about as easily as the austenitic stainless steels. It is not nearly so prone to work hardening as the other nickel alloys like the Hastelloys. It is one of the preferred materials used in light water fission plants and holds up quite well to neutron bombardment.

I think a Inconel 690-copper-Inconel 690 laminate for the Hot Water jacket, Kieth calls it the "first wall", is quite doable. I think I have come up with a way to make the longitudnal seam welds on such a jacket that would hold as well as if we were seam welding sold Inconel 690. However, such a joint would need to be fabricated and tested for us to be certain.

Kiteman is right about my transferring the mechanical loads through the jackets to the vacuum vessel walls. I am still working on the six big solenoids locked in a sumo contest and do not see any other way to deal with the loads with that configuration.

Chief Simon, I wonder if you would be good enough to think about this stuff:

http://en.wikipedia.org/wiki/Yttrium_ba ... pper_oxide

If we could make Bitter Plates with this material we could eliminate the need for LHe. I don't know if that is in the realm of possibility, but it would make life a lot simpler if it is.

I have managed to squeeze out a little time for this project here and there and have finished with the trickier pieces. I hope to have more pictures for everyone to look at soon.

Thank you all for your patience,

Billy.