Magnet Design

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

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KitemanSA
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Magnet Design

Post by KitemanSA »

MSimon wrote:We can start out with a 10 Tesla coil 2 meters in dia. 16 million ampere turns. Figure a Jc of 10,000 A/sq cm That is 1,600 sq cm. That makes a radius of 29 cm just for the superconductors.
I recently ran across an article that implied 10E5A/cm^2 for MgB2 at LHe temperatures. That would make the core more like 10cm radius. The abstract of the paper from Japan reads:
The paper reports the first successful fabrication of MgB2 superconducting tape using a flexible metallic substrate as well as its strong pinning force, which was verified by direct measurement of transport critical current density. The tape was prepared by depositing MgB2 film on a Hastelloy tape buffered with an YSZ layer. The Jc of the tape exceeds 10^5A/cm2 at 4.2K and 10T, which is considered as a common benchmark for magnet application. The Jc dependence on magnetic field remains surprisingly very small up to 10T, suggesting that the tape has much better magnetic field characteristic than conventional Nb-Ti wires in liquid helium.
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MSimon
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Re: Magnet Design

Post by MSimon »

KitemanSA wrote:
MSimon wrote:We can start out with a 10 Tesla coil 2 meters in dia. 16 million ampere turns. Figure a Jc of 10,000 A/sq cm That is 1,600 sq cm. That makes a radius of 29 cm just for the superconductors.
I recently ran across an article that implied 10E5A/cm^2 for MgB2 at LHe temperatures. That would make the core more like 10cm radius. The abstract of the paper from Japan reads:
The paper reports the first successful fabrication of MgB2 superconducting tape using a flexible metallic substrate as well as its strong pinning force, which was verified by direct measurement of transport critical current density. The tape was prepared by depositing MgB2 film on a Hastelloy tape buffered with an YSZ layer. The Jc of the tape exceeds 10^5A/cm2 at 4.2K and 10T, which is considered as a common benchmark for magnet application. The Jc dependence on magnetic field remains surprisingly very small up to 10T, suggesting that the tape has much better magnetic field characteristic than conventional Nb-Ti wires in liquid helium.
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The number I came up with was based on some early studies done on MgB at 20K. At 4K there may be less dependence of Jc on B.
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KitemanSA
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Re: Magnet Design

Post by KitemanSA »

MSimon wrote: The number I came up with was based on some early studies done on MgB at 20K. At 4K there may be less dependence of Jc on B.
If we are using LHe and the only heat is coming from outside, aren't we pretty much going to be at 4.7K?

By the way, the article did mention the PIT wire drawn MgB2 as being about the number you mentioned.

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Re: Magnet Design

Post by MSimon »

KitemanSA wrote:
MSimon wrote: The number I came up with was based on some early studies done on MgB at 20K. At 4K there may be less dependence of Jc on B.
If we are using LHe and the only heat is coming from outside, aren't we pretty much going to be at 4.7K?

By the way, the article did mention the PIT wire drawn MgB2 as being about the number you mentioned.
Do you have a link? Or can you e-mail me the article?

My e-mail is on the top of the sidebar at:

http://iecfusiontech.blogspot.com/
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KitemanSA
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Re: Magnet Design

Post by KitemanSA »

MSimon wrote: Do you have a link? Or can you e-mail me the article?
http://arxiv.org/abs/cond-mat/0203113

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Re: Magnet Design

Post by MSimon »

KitemanSA wrote:
MSimon wrote: Do you have a link? Or can you e-mail me the article?
http://arxiv.org/abs/cond-mat/0203113
Thanks!

The problem with the Hastelloy tape is that it has significant amounts of Cobalt which is a no-no in neutron flux environments.

However, improved flux pinning with the addition of Carbon to the MgB seems to have promise.
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KitemanSA
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Re: Magnet Design

Post by KitemanSA »

MSimon wrote: The problem with the Hastelloy tape is that it has significant amounts of Cobalt which is a no-no in neutron flux environments.
?? Wha?? Why then is it so widely used in reactor applications? It was the metal of choice for the MSR in the 60s.

I hope you are just saying that better alloys have come along!

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Re: Magnet Design

Post by MSimon »

KitemanSA wrote:
MSimon wrote: The problem with the Hastelloy tape is that it has significant amounts of Cobalt which is a no-no in neutron flux environments.
?? Wha?? Why then is it so widely used in reactor applications? It was the metal of choice for the MSR in the 60s.

I hope you are just saying that better alloys have come along!
I was under the impression that this alloy was used for facings of valves and other situations where it would not make up bulk metal. And it is also alloy dependent. Some of the Hastelloy alloys are lower in Cobalt than others.

Also I believe that Hastelloy is not used in high flux areas like reactor vessels.

The alloy used in the SC experiments is not low Cobalt (less than .2%) it is in the 2% range.

As far as other possibilities - for MgB SCs Carbon in small quantities (under 5%) is used for flux pinning.
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KitemanSA
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Post by KitemanSA »

From Wikipedia:Molten Salt Reactor:Molten Salt Reactor Experiment
The MSRE was located at ORNL. Its piping, core vat and structural components were made from Hastelloy-N

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Post by MSimon »

KitemanSA wrote:From Wikipedia:Molten Salt Reactor:Molten Salt Reactor Experiment
The MSRE was located at ORNL. Its piping, core vat and structural components were made from Hastelloy-N
http://www.suppliersonline.com/property ... elloyN.asp

Cobalt .2% max

That is not true of the alloy the SC guys used. It was 2% Co.

===

The reason for keeping Co low is that it reduces the need for "jumpers" to do reactor work after shutdown.

If shutdowns need to be frequent (esp important for experimental work) you want activation products with a half life of about a day or two max. And the amount of two day products should be minimized. For fission nukes 10 days is sufficient to give 15 minute access to the reactor compartment. Of course you have fission products to deal with where you have no choice. In a BFR almost everything is choice.
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KitemanSA
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Post by KitemanSA »

So we get them to put it on HastelloyN tape. Or even stainless steel. I think it is more the manufacturing method than the base material. American Supercondutors puts their YBCO on three different bases. The point is that at LHe temps, the material is suggesting 10^5 A/cm^2. This is NOT yet a commercial material though, AFAIK.

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Post by MSimon »

KitemanSA wrote:So we get them to put it on HastelloyN tape. Or even stainless steel. I think it is more the manufacturing method than the base material. American Supercondutors puts their YBCO on three different bases. The point is that at LHe temps, the material is suggesting 10^5 A/cm^2. This is NOT yet a commercial material though, AFAIK.
I certainly agree that experiments need to be done. If the tape is rated at a Jc of 1E5, operationally you probably want to design for a current density of 5E4. A reduction of volume by a factor of 5 would certainly be a good thing. Not to mention weight savings intrinsic to the reduction. And a reduction of support structure.
Engineering is the art of making what you want from what you can get at a profit.

VernonNemitz
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An oddball notion

Post by VernonNemitz »

Years ago, when I first heard about Bussard wanting to modify the Farnsworth-Hirsch design by using magnetic fields, there wasn't enough data for me to know what he had in mind, so I began to imagine....

This notion therefore may be totally off-the-wall and useless. It may have some entertainment value, though, so...

Have you ever seen an incandescent light-bulb filament under a magnifier? Tungsten is actually a pretty good electrical conductor, so a long long filament is needed to get enough electrical resistance. To fit such a long filament into the bulb, the filament is coiled, and then the coiled filament is coiled again. Some high-output bulbs have a third level of coiling of the filament.

What if the electrostatic grid in a Fusor was coiled, and a DC current fed through it? Then it would have a magnetic field that should mostly deflect collision-course ions. This idea would require that the entire electrical circuit be isolated from other circuits (including parts of it outside the Fusor), so that its wiring, as a whole, can be given an electrostatic charge (and DC induced to flow through it), but I don't see that as a particularly difficult thing to accomplish.

I do think there still might be a few spots where ions could impact the grid. Will enough of them be deflected to make the Fusor practical? I have no idea...have fun!

KitemanSA
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Post by KitemanSA »

Vernon,
would you please delete your posting here and repost as a new topic? It really doesn't track with this subject.
Thanks

VernonNemitz
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Post by VernonNemitz »

KitemanSA wrote:Vernon,
would you please delete your posting here and repost as a new topic? It really doesn't track with this subject.
Thanks
I don't see a "delete" button anywhere? Am I supposed to "Edit" it until nothing remains? BTW, I picked this Topic area because it IS about "magnet design" even if it has nothing to do with the Polywell idea.

--peculiarly, I see a delet button for THIS post...(just after having posted it).

--experiment: after the next message was posted, the delete button disappeared. Will it return if this is edited?

Nope.

To MSimon, yes, it is OK to move the message to a new topic (AND to delete this one afterward!). Topic suggestion: "Adding Magnetism to a Fusor"
Last edited by VernonNemitz on Fri Jun 05, 2009 5:01 pm, edited 3 times in total.

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