MgB SC Improvements

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MSimon
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MgB SC Improvements

Post by MSimon »

Significant improvement of critical current density in MgB2 doped with ferromagnetic Fe3O4 nanoparticles

B Qu, X D Sun, J-G Li, Z M Xiu, S H Liu and C P Xue
2009 Supercond. Sci. Technol. 22 015027 (4pp)
Abstract: http://www.iop.org/EJ/abstract/-alert=3 ... 2/1/015027
Full text PDF: http://www.iop.org/EJ/article/-alert=34 ... 015027.pdf
Ferromagnetic Fe3O4-doped MgB2 bulks were first fabricated in this work by the hot pressing method. It was found that Fe3O4 does not react with Mg or B during the fabrication process. Peak Jc values of the 5 wt% Fe3O4-doped MgB2 are higher than 10E6 A cm−2 in the temperature range 5-30 K. Especially at 30 K, the peak Jc is 1.02 x 10E6 A cm−2 for the 5 wt% Fe3O4-doped MgB2, the highest values at 30 K found in the literature, and about seven times that of the 5 wt% SiC-doped MgB2 sample. The drop in Jc with increasing field for the Fe3O4-doped MgB2 is significantly slower than that of the SiC-doped MgB2 at 30 K. These results indicate that the Fe3O4-doped MgB2 is a potential superconductor to be used at temperatures greater than 25 K which is a critical temperature for large-scale practical applications.
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JohnP
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Post by JohnP »

Why is 25K+ so important? Does it have to do with liquid neon vs liquid helium?

pstudier
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Post by pstudier »

JohnP wrote:Why is 25K+ so important? Does it have to do with liquid neon vs liquid helium?
My guess is that it allows the use of hydrogen, which boils at 20.28K. Neon is expensive.
Fusion is easy, but break even is horrendous.

JohnP
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Post by JohnP »

So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?

MSimon
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Post by MSimon »

JohnP wrote:So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?
LN2 is about $1 per liter. Less in high volume. A truckload (I think around 25,000 liters) is about $.75 a liter. I have also seen numbers between $.10 and $.50 per liter. LN2 is .81 kg/l. The $.75 price assumes a 100 mi shipping distance from the LN2 plant.

N2 goes solid at about 66K. Above 120K it can't be liquefied at any pressure.

I have no idea what LH costs. I have seen estimates of $4 a kg. produced. Sales at low volume would probably be double that. It boils at about 20K. Its density is about .071 kg/l. It takes 50 KWh to produce a kg of LH2. So you can figure it on that basis. Shipping and capital costs extra.
Engineering is the art of making what you want from what you can get at a profit.

cuddihy
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Post by cuddihy »

MSimon wrote:
JohnP wrote:So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?
LN2 is about $1 per liter. Less in high volume. A truckload (I think around 25,000 liters) is about $.75 a liter. I have also seen numbers between $.10 and $.50 per liter. LN2 is .81 kg/l. The $.75 price assumes a 100 mi shipping distance from the LN2 plant.

N2 goes solid at about 66K. Above 120K it can't be liquefied at any pressure.

I have no idea what LH costs. I have seen estimates of $4 a kg. produced. Sales at low volume would probably be double that. It boils at about 20K. Its density is about .071 kg/l. It takes 50 KWh to produce a kg of LH2. So you can figure it on that basis. Shipping and capital costs extra.
So for a small, light, "air-worthy" polywell, the key is really a superconductor that stays SC to ~90-95 K? (that way it could be cooled by LN without too much heavy stuff)
Tom.Cuddihy

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MSimon
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Post by MSimon »

cuddihy wrote:
MSimon wrote:
JohnP wrote:So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?
LN2 is about $1 per liter. Less in high volume. A truckload (I think around 25,000 liters) is about $.75 a liter. I have also seen numbers between $.10 and $.50 per liter. LN2 is .81 kg/l. The $.75 price assumes a 100 mi shipping distance from the LN2 plant.

N2 goes solid at about 66K. Above 120K it can't be liquefied at any pressure.

I have no idea what LH costs. I have seen estimates of $4 a kg. produced. Sales at low volume would probably be double that. It boils at about 20K. Its density is about .071 kg/l. It takes 50 KWh to produce a kg of LH2. So you can figure it on that basis. Shipping and capital costs extra.
So for a small, light, "air-worthy" polywell, the key is really a superconductor that stays SC to ~90-95 K? (that way it could be cooled by LN without too much heavy stuff)
Maybe. That assumes "use once, exhaust to atmosphere". If you have a closed system then the costs come down because you are not reliquefying from 300K. MRIs use a closed system. 2 loops - LHe and LN2. For Polywell we would use a 4 loop system LHe, LN2, H2O 300degK, H2O 600degK.
Engineering is the art of making what you want from what you can get at a profit.

pstudier
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Post by pstudier »

MSimon wrote:
JohnP wrote:So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?
I have no idea what LH costs. I have seen estimates of $4 a kg. produced. Sales at low volume would probably be double that. It boils at about 20K. Its density is about .071 kg/l. It takes 50 KWh to produce a kg of LH2. So you can figure it on that basis. Shipping and capital costs extra.
If I understand this to be $4/kg is for the gas, and 50 KWh to liquefy it, at $0.1/Kwh, this comes to $0.28/l for H2 and $0.36 to liquefy it for a total of $0.64. From http://www.phys.ufl.edu/~cryogenics/hecost.htm , liquid Helium costs At least ~$5.00US/liquid liter in 100 liter or more quantities in the US but much more expensive elsewhere. Add to that concerns that the Helium will eventually run out, and I would presume a closed cycle Hydrogen refrigerator would be less expensive than a Helium one. Finally the heat of vaporization of Hydrogen is 0.904 kJ·mol−1, compared to Helium, which is 0.0829 kJ·mol−1. So you get 10 times the cooling from a mole of Hydrogen over that from Helium.
Fusion is easy, but break even is horrendous.

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Post by MSimon »

He has it over H2 when it comes to explosive mixtures with atmospheric oxygen.

I think that can be dealt with in an operational plant. But it raises the cost of everything. Intrinsic safety is expensive.
Engineering is the art of making what you want from what you can get at a profit.

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