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MgB SC Improvements
Posted: Sat Jan 24, 2009 7:49 am
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.
Posted: Sun Jan 25, 2009 2:40 am
by JohnP
Why is 25K+ so important? Does it have to do with liquid neon vs liquid helium?
Posted: Sun Jan 25, 2009 7:10 am
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.
Posted: Mon Jan 26, 2009 3:30 am
by JohnP
So liquid H is cheaper than He? Just out of curiousity, how do they compare with LN2?
Posted: Mon Jan 26, 2009 4:09 am
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.
Posted: Mon Jan 26, 2009 4:48 am
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)
Posted: Mon Jan 26, 2009 5:02 am
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.
Posted: Tue Jan 27, 2009 5:33 am
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.
Posted: Tue Jan 27, 2009 6:53 am
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.