MgB SC Improvements

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

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MSimon
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MgB SC Improvements

Post by MSimon »

From:

http://www.iop.org/EJ/toc/-alert=34023/0953-2048/22/8

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http://www.iop.org/EJ/abstract/-alert=3 ... 2/8/085002
Cold high pressure densification was found to substantially enhance the critical current density of binary in situ Fe/MgB2 wires. A wire densified at 1.85 GPa exhibited at 20 K and 5 T an increase of Jc by 300% with respect to same wire without the application of pressure. At 4.2 K and 10 T, Jc was found to be increased by 53%. The decrease of the electrical resistance for densified wires reflects an improved connectivity. The values of Birr at 4.2 and 20 K were enhanced up to 0.7 T for densified wires.

After applying pressures up to 6.5 GPa at 300 K, the relative mass density dm of the unreacted (B+Mg) mixture inside the filament increased up to 96% of the theoretical density. This corresponds to a relative mass density df in the reacted MgB2 filaments of 73%. A quantitative correlation between filament mass density and critical current density was established.
http://www.iop.org/EJ/abstract/-alert=3 ... 2/8/085015
Combined with the thermal analysis and phase identification, the sintering process of nano-SiC-doped MgB2 samples was systemically investigated. Accordingly, a new consideration for the mechanism of enhanced electromagnetic properties of nano-SiC-doped MgB2 is proposed, which is more consistent with the observed experimental results of nano-SiC-doped MgB2 samples sintered at different temperatures and has many advantages over the previous model in explaining the experimental observations.
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chrismb
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Post by chrismb »

Superconducting wire is all very interesting for the research reactors, but surely will be no use for widespread and ubiquitous adoption of such technology? Unless the super conductors can work at 70K, with liquid nitrogen, as the availability of helium is limited and once used cannot be re-manufactured. (If you think the fusion process itself could re-manufacture enough He then I'd be interested in seeing that calculation.)

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Post by MSimon »

chrismb wrote:Superconducting wire is all very interesting for the research reactors, but surely will be no use for widespread and ubiquitous adoption of such technology? Unless the super conductors can work at 70K, with liquid nitrogen, as the availability of helium is limited and once used cannot be re-manufactured. (If you think the fusion process itself could re-manufacture enough He then I'd be interested in seeing that calculation.)
A 100 MWth BFR will consume about 200g/day of B11. That means about 200g/day of helium. The numbers are roughly similar with D-D.

That should be more than enough to replace losses and provide excess for new reactors.

MRIs use He and the loss rate is about 1 liter a month. (IIRC) and in fact some of them do away with the LHe and do conduction cooling.
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tombo
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Post by tombo »

There is also a reversible increase in SC properties with pressure for some SC's. (MgB2 ?)
The kinds of fields we are generating could if supported correctly provide some serious compression to the SC and enhance the Jc.
It is one more tweak that might help enough to be worth the trouble.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

chrismb
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Post by chrismb »

MSimon wrote:
chrismb wrote:Superconducting wire is all very interesting for the research reactors, but surely will be no use for widespread and ubiquitous adoption of such technology? Unless the super conductors can work at 70K, with liquid nitrogen, as the availability of helium is limited and once used cannot be re-manufactured. (If you think the fusion process itself could re-manufacture enough He then I'd be interested in seeing that calculation.)
A 100 MWth BFR will consume about 200g/day of B11. That means about 200g/day of helium. The numbers are roughly similar with D-D.

That should be more than enough to replace losses and provide excess for new reactors.

MRIs use He and the loss rate is about 1 liter a month. (IIRC) and in fact some of them do away with the LHe and do conduction cooling.
maybe so, but there again an MRI magnet isn't sitting inside a MW reactor core!!...

I think the numbers will remain unknown on that point, until such a thing is running.

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Post by MSimon »

chrismb wrote:
MSimon wrote:
chrismb wrote:Superconducting wire is all very interesting for the research reactors, but surely will be no use for widespread and ubiquitous adoption of such technology? Unless the super conductors can work at 70K, with liquid nitrogen, as the availability of helium is limited and once used cannot be re-manufactured. (If you think the fusion process itself could re-manufacture enough He then I'd be interested in seeing that calculation.)
A 100 MWth BFR will consume about 200g/day of B11. That means about 200g/day of helium. The numbers are roughly similar with D-D.

That should be more than enough to replace losses and provide excess for new reactors.

MRIs use He and the loss rate is about 1 liter a month. (IIRC) and in fact some of them do away with the LHe and do conduction cooling.
maybe so, but there again an MRI magnet isn't sitting inside a MW reactor core!!...

I think the numbers will remain unknown on that point, until such a thing is running.
Yes. But the LHe that boils off can be recycled. At least in the early stages LHe losses are the least of our worries. And if LHe is a problem for the BFR think of how much worse it will be for an operational tokamak with a Li blanket.
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D Tibbets
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Post by D Tibbets »

I know little of the details, but if the superconducting magnets will work at ~ 15 degrees K, then couldn't liquid hydrogen be used. Not quite as cold a liquid helium can reach, but alot closer than liquid nitrogen.


Dan Tibbets
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MSimon
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Post by MSimon »

D Tibbets wrote:I know little of the details, but if the superconducting magnets will work at ~ 15 degrees K, then couldn't liquid hydrogen be used. Not quite as cold a liquid helium can reach, but alot closer than liquid nitrogen.

Dan Tibbets
Yes. It would work down to around 4.2K. But then you have the problem of safety. Everything in the reactor room would need to be designed intrinsically safe. It adds cost.
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tombo
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Post by tombo »

And Helium doesn't add cost?

Hydrogen safety is workable.
They even manage to use it to cool the large generators (up to 600MW) in (probably all) major power plants. We will be needing it on that side of the plant anyway.

I think cooling the SC with liquid H2 and the other layers with gas H2 might be the way to go. It's viscosity makes up for its low density and it has good heat capacity. It is clean. A leak into the vacuum chamber would not be as catastrophic to clean up as water or ethylene glycol or NaK.

If PW is to be used to fuel a hydrogen economy then those problems will need to be worked out in mass. But for experiments H2 is used in labs all the time. Just keep it away from oxygen. Mixtures <~4% or >~85% are just fine. Ask you local Air Liquide salesman for guidelines. And don't forget to deploy flammable gas detectors next to all the smoke detectors etc. Don't fall prey to the Hindenburg propaganda.

As far a intrinsically safe I think only the stuff inside the ventilated H2 piping cabinets would need that.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

Torulf2
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Post by Torulf2 »

Many yeas ago I was working in a chemical factory how used H2 in the processes.
There were sensors and alarms everywhere. At the lab I worked in, we used palladium powder. And the lab worker was not allowed to work in that part of the factory how used H2.
If we had Pd in the clothing a leakage of H2 should explode threw the catalytic power of the Pd.

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Post by MSimon »

tombo wrote:And Helium doesn't add cost?

Hydrogen safety is workable.
They even manage to use it to cool the large generators (up to 600MW) in (probably all) major power plants. We will be needing it on that side of the plant anyway.

I think cooling the SC with liquid H2 and the other layers with gas H2 might be the way to go. It's viscosity makes up for its low density and it has good heat capacity. It is clean. A leak into the vacuum chamber would not be as catastrophic to clean up as water or ethylene glycol or NaK.

If PW is to be used to fuel a hydrogen economy then those problems will need to be worked out in mass. But for experiments H2 is used in labs all the time. Just keep it away from oxygen. Mixtures <~4% or >~85% are just fine. Ask you local Air Liquide salesman for guidelines. And don't forget to deploy flammable gas detectors next to all the smoke detectors etc. Don't fall prey to the Hindenburg propaganda.

As far a intrinsically safe I think only the stuff inside the ventilated H2 piping cabinets would need that.
Uh. Nope. I have designed intrinsically safe eqpt. for Amocams oil field monitoring (it was a subsidiary of AMOCO) and Robert Shaw (refinery controls). You have to use it in any space where hydrogen is present. Special conduit for power. All communications wiring intrinsically safe. Capacitance and inductance limits on the wiring. Current and power limits. Voltage limits. Non-sparking tools. All eqpt not IS must be sealed. Special procedures for opening such eqpt. Then you need a "range safety officer" to monitor procedures. It is a real pain.

Now imagine making that work in the presence of 200 KV 25 A power supplies. It is going to cost more than a nickel.

I wouldn't use it in the first couple of hundred plants. Explosions are bad publicity.

I wouldn't use it in experimental reactors no matter what.

In any case if we need to get down to 2K for the fields we want the whole thing is moot.
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tombo
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Post by tombo »

When I worked in semiconductors we had a 40 foot H2 tank permanently parked at the loading dock right next to the one for N2.
There were simple safety procedures. And we followed them carefully for obvious reasons. Other stuff we had was much nastier.
Only trained people could handle it. All piping cabinets were thoroughly ventilated.
There were 1000 degree C parts IN the H2, heated with 35kW RF induction heaters.
Nothing was officially "intrinsically safe" it couldn't be to get the reaction conditions we needed.
We had welding going on in an adjacent room.
There was never even the smallest problem or accident with the H2 flammability.

The 100MW H2 cooled generators can't be "intrinsically safe" either.
Somebody knows how to do it safely.
It has to be used in the thermal recovery plant at full power scale.
It is standard technology.

If we can do PW with the fields at 20K that is a lot easier to get to than 4K.
Neon at 27K is a lot safer but does not carry the heat as well.

Avoiding pushing the envelope to the most extreme temperatures relieves many design problems.
There is a large multiplier on its effects as I will explain in future post when I get more ducks in a row.
-Tom Boydston-
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Post by MSimon »

Avoiding pushing the envelope to the most extreme temperatures relieves many design problems.
True. But there is that B^4. A 10% increase in field gets you a 46% increase in output. If you can get that from going to 2K from 4K it probably pays.

And 2K is becoming the leading edge standard vs formerly 4K.

In any case I would only do something like that for production. For experimental work you want to be able to make changes on the fly without a full up engineering review.
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