Where in the magnets are the field lines?

[blaisepascal]

Someone tell me what I'm missing....

My understanding is that high Tc superconductors have problems with large currents in large magnetic fields. As MSimon said in another thread, the field lines interfere with Cooper Pair formation, and it just doesn't work very well. This is viewed as a limit on the strength of the coils using high Tc superconductors.

Superficially, I can see it -- we are trying to create a high field strength coil, superconductors don't work well at high field strength and high temperatures, so we need either better superconductors or better cooling.

But what's been bugging me the past few days of hearing this discussion is... In the coil, there are no field lines entering the conductor. The field lines circulate around the coil, not through it (at least, for conformal coils, which are what's planned). So how is the B field killing the superconductors?

[Art Carlson]

If you ignore the casing, cooling, etc., then magnetic flux lines never penetrate a (Type I) superconductor (very far). But there is always a surface of contact between the superconductor and the field, even when the field is parallel to the surface. The magnetic field on this surface must not exceed the critical field.

[KitemanSA]

If you ignore the casing, cooling, etc., then magnetic flux lines never penetrate a (Type I) superconductor (very far).

Aren't HTSs Type II superconductors? The fields enter Type II a lot more, but are confined to "flux tubes" IIRC. I hope I got that right. It is still a bit confusing to me.

[eros]

Superconducting magnets generating field depends only inside currents. Only limiting thing is critical current. High fields itselfs are not limit, but they generate repulsion currents. You can find some proof with "freezing fields" words. Sc internal structure and current loops say how well it performs. Type2 Sc are hard because micro loops that eat almost all of critical current value.

--Eerin

[JohnP]

My understanding is that high Tc superconductors have problems with large currents in large magnetic fields. As MSimon said in another thread, the field lines interfere with Cooper Pair formation, and it just doesn't work very well. This is viewed as a limit on the strength of the coils using high Tc superconductors.

As far as I've seen, the high Tc superconductors you refer to won't be used for Polywell. More traditional superconductors, like those used in MRI's, would be.

[blaisepascal]

My understanding is that high Tc superconductors have problems with large currents in large magnetic fields. As MSimon said in another thread, the field lines interfere with Cooper Pair formation, and it just doesn't work very well. This is viewed as a limit on the strength of the coils using high Tc superconductors.

As far as I've seen, the high Tc superconductors you refer to won't be used for Polywell. More traditional superconductors, like those used in MRI's, would be.

High Tc superconductors would be used if they would work. But since high Tc superconductors have a problem with high fields and high currents, it isn't believed that they will work in this application.

MSimon is interested in working with "more traditional superconductors, like those used in MRI's" because they are a proven, mature, technology, not because working with low Tc superconductors is somehow important to the Polywell concept.

[MSimon]

My understanding is that high Tc superconductors have problems with large currents in large magnetic fields. As MSimon said in another thread, the field lines interfere with Cooper Pair formation, and it just doesn't work very well. This is viewed as a limit on the strength of the coils using high Tc superconductors.

As far as I've seen, the high Tc superconductors you refer to won't be used for Polywell. More traditional superconductors, like those used in MRI's, would be.

High Tc superconductors would be used if they would work. But since high Tc superconductors have a problem with high fields and high currents, it isn't believed that they will work in this application.

MSimon is interested in working with "more traditional superconductors, like those used in MRI's" because they are a proven, mature, technology, not because working with low Tc superconductors is somehow important to the Polywell concept.

Yes.

Although I'm kind of partial to MgB these days. Even so its Tc is about 40K and operationally they would have to be cooled to the 4K to 20K region to support the desired fields.

But for experimental purposes I'd go with MRI magnets. At least the first time around. Off the shelf technology - in a nearly ready to go form.