Room Temperature Superconductors One Step Closer

We are one step closer to room temperature superconductors.

Menlo Park, Calif.—Move over, silicon—it may be time to give the Valley a new name. Physicists at the Department of Energy's (DOE) SLAC National Accelerator Laboratory and Stanford University have confirmed the existence of a type of material that could one day provide dramatically faster, more efficient computer chips.

Recently-predicted and much-sought, the material allows electrons on its surface to travel with no loss of energy at room temperatures and can be fabricated using existing semiconductor technologies. Such material could provide a leap in microchip speeds, and even become the bedrock of an entirely new kind of computing industry based on spintronics, the next evolution of electronics.

Physicists Yulin Chen, Zhi-Xun Shen and their colleagues tested the behavior of electrons in the compound bismuth telluride. The results, published online June 11 in Science Express, show a clear signature of what is called a topological insulator, a material that enables the free flow of electrons across its surface with no loss of energy.

Pretty darn exciting. It all depends on something called topological insulation. The article gives some details on how that works. Which gets a bit heavy on the physics. I'm going to skip that here. However, if you have heard of the Pauli exclusion principle it is worth a read.

There are some limitations. For now.

Topological insulators aren't conventional superconductors nor fodder for super-efficient power lines, as they can only carry small currents, but they could pave the way for a paradigm shift in microchip development. "This could lead to new applications of spintronics, or using the electron spin to carry information," Qi said. "Whether or not it can build better wires, I'm optimistic it can lead to new devices, transistors, and spintronics devices."

Fortunately for real-world applications, bismuth telluride is fairly simple to grow and work with. Chen said, "It's a three-dimensional material, so it's easy to fabricate with the current mature semiconductor technology. It's also easy to dope—you can tune the properties relatively easily."

"This is already a very exciting thing," he said, adding that the material "could let us make a device with new operating principles."

Bismuth Telluride is a semiconductor that is currently used for solid state refrigerators. It is also used to generate electricity from small temperature differences. That means the semiconductor industry has more than a little experience in fabricating the material.

If the lab boys have developed a repeatable formula it is possible we might see useful devices using this superconducting property in as little as three years. One use of such properties might be to make a super low noise microwave filter that doesn't require cooling to Liquid Nitrogen temperatures (77° Kelvin). That could be very helpful.

I will be keeping an eye on this one.

If "normal" superconductivity interests you this book is a good place to start:
Introduction to Superconductivity

And if you are a little further along and contemplate building a fusion reactor in your garage, this book could help:
Case Studies in Superconducting Magnets: Design and Operational Issues

More books:

Superconductivity

Handbook of Superconductivity

Engineering Superconductivity

A Big Motor For The Electric Navy

Here is something I should have posted here a while ago.


Last week I did a post on the the science of electric motors that featured a learning kit for kids that provided the parts required for a kid (of any age) interested in the science and technology of electric motors to build a small one. I'd estimate that the motor, which you could hold in in the palm of your hand, produced less than 1/1,000th of a horsepower. Here is a motor whose power is about ten orders of magnitude bigger. And that is a whole lot bigger.

The Next Big Future reports on the really big motor that uses high temperature superconductors.

American Superconductor Corporation, a leading energy technologies company, and Northrop Grumman Corporation announced today at the Surface Navy Association’s 21st National Symposium the successful completion of full-power testing of the world’s first 36.5 megawatt (49,000 horsepower) high temperature superconductor (HTS) ship propulsion motor at the U.S. Navy’s Integrated Power System Land-Based Test Site in Philadelphia. This is the first successful full-power test of an electric propulsion motor sized for a large Navy combatant and, at 36.5 megawatts, doubled the Navy’s power rating test record.

The Business Wire tells a little more of the story.

This system was designed and built under a contract from the Office of Naval Research to demonstrate the efficacy of HTS motors as the primary propulsion technology for future Navy all-electric ships and submarines. Naval Sea Systems Command (NAVSEA) funded and led the successful testing of the motor.

Incorporating coils of HTS wire that are able to carry 150 times the power of similar-sized copper wire, the motor is less than half the size of conventional motors used on the first two DDG-1000 hulls and will reduce ship weight by nearly 200 metric tons. It will help make new ships more fuel-efficient and free up space for additional warfighting capability.

“The successful load test of our HTS motor marks the beginning of a new era in ship propulsion technology,” said Dan McGahn, senior vice president and general manager of AMSC Superconductors. “This motor provides the U.S. Navy with a truly transformational capability relative to size, stealth, endurance and survivability, providing our Navy with a clear performance advantage for years to come. We are grateful for the steadfast support from the Office of Naval Research, Naval Sea Systems Command and the Naval Surface Warfare Center.”

A different branch of the Navy, Naval Air Warfare Center Weapons Division, is funding work that may lead to a shipborne fusion power reactor. Which would be kinda handy to have to power two or four of those electric motors turning the screws of an aircraft carrier. You can read about the latest contract for development of the Bussard Naval Fusion Reactor at IEC Fusion Technology.

And that is not the only electric propulsion system that future aircraft carriers will use. There is also the electric catapult being developed by General Atomics (GA).

GA and its Team have completed the Program Definition and Risk Reduction (PDRR) phase of the Navy's electromagnetic aircraft launch system (EMALS) program and have been selected to perform the System Development and Demonstration phase. The goal of the EMALS SDD phase is to develop the existing design chosen during PDRR into an integrated shipboard system that is both operationally suitable and effective, thus replacing steam catapults with an electric system that will reduce maintenance and provide flexibility and growth potential for carrier aviation throughout the 21st century.The GA Team EMALS design is a robust, highly reliable launch system that will meet or exceed all Navy performance goals. This design will provide significant reductions in installed weight, volume, and workload compared to the existing steam catapult. The design uses state-of-the-art technologies that we believe will demonstrate our system is affordable and producible.

There are more details at the link.

And guess what else the US Navy is working on? A real honest to God beam weapon. The Free Electron Laser

The Navy is pushing ahead with a five-year, $163 million dollar plan to bring the "Holy Grail" of energy weapons up to battlefield strength.

For decades, scientists have been slowly working on a laser that never runs out of shots -- and can be "tuned" to blast through the air, at just the right wavelength. For most of that time, all they could get was a laser at lightbulb-strength. But in 2004, researchers at the Thomas Jefferson National Accelerator Facility finally managed to assemble a "Free Electron Laser," or FEL, that could generate 10,000 watts of power. Now, the Navy has started an effort to design and build a new FEL, 10 times as strong. That would bring the laser up to 100 kilowatts -- what's considered the minimum threshold for weapons-grade. But it would also be just a stepping stone, on the way to an energy weapon as powerful as any produced. If ray gun researchers can get the thing to work, that is.

And lest we leave out projectile weapons how about an offshoot of the electric aircraft catapult. The rail gun which fires projectiles with electricity at a muzzle velocity of better than 8,000 ft per second.

The Navy is researching rail guns because they would weigh less than conventional ones, and since they rely on electromagnetics to fire rounds, you wouldn't need a big, dangerous pile of explosives stored in a magazine. All of that means a lighter ship, and a much more deadly ship: a combat-ready rail gun would be able to fire Mach 5 projectiles over 200 miles with pinpoint accuracy, hitting 5 meter targets.

Yesterday's test firing at the Naval Surface Warfare Center Dahlgren Division used just some of the potential 32-megajoules the laboratory test gun is capable of, and that's only half the 64-megajoules the Navy is aiming at for the final weapon.

If you follow the link you can watch some really cool videos.

It looks like the US Navy has a plan. And you know? I just love it when a plan comes together.

H/T just_an_observer at Talk Polywell

WB-100 Superconductor Magnet Cooling

I have been working on some of the cooling issues for WB-100 - the 100 MW test reactor using superconducting magnets.

The magnet will consist of a series of concentric pipes. The innermost will contain the superconductor and its coolant at 20K. Next will come a vacuum space and next will come LN coolant. In the vacuum space between the superconductor coolant and the LN coolant the walls will be silvered (or some such) to minimize the radiative heat flow between the superconductor coolant and the LN. Think thermos bottle.

Next space after LN coolant will be another vacuum space. It too will be silvered. Then H2O coolant at around 300K. Another silvered vacuum space. And finally H2O coolant at around 600K.

What we are going to have is a series of concentric vacuum bottles with LHe at 20K at the center and H2O at 600K at the outside. All this plumbed to allow enough flow to keep everything at the proper temperature.

Let me add that any electrons ejected from the surface of this contraption will carry away minimal energy. The alphas will be hitting with 2MeV+. The electrons (those that are not lost due to high energy) will be at 50KeV.

My current plan is to coat the outer surface of the coils with Boron which melts at 2349 K. The purpose is to prevent sputtering of the metallic pipes holding the coolant so the only material sputtered into the reactant space will be a reactant - B11. It has been suggested at Coulter Smithing that an outer sheath for the coil of Titanium might work well since any sputtered atoms would act as a getter. OTOH it might poison the reaction. Lots of unknowns here. We may just have to build one and see what happens.

If we use Boron, we will have to figure out how to balance Boron condensation on the outer magnet structure with Boron sputtering from the reaction.

Below is a picture of a cross section of the superconducting coil.

Update: 06 Feb 008 2046z

I was thinking. Since for a power reactor we will need to water cool the coils. Suppose we made the water jacket thick enough to thermalize neutrons. And then had a B10 layer to absorb them.

It should be possible to cut way down on coil damage and still run superconductors in a D-D machine.

MgB is interesting in that it becomes a better superconductor with some neutron damage

With MgB the resistivity goes up. Critical Field goes up. And critical temperature declines slightly.

The main problem seems to be defects caused by B10 absorbing neutrons.

If B10 was used in shielding and B11 used to make the superconducting wire much longer lifetimes in neutron fluxes should be possible.

The the cross section difference is six orders of magnitude B10 to B11. With B10 @ 10,000 barns at .025 eV and B11 @ .01 barns.

Magnesium has a cross section of about .75 for 2.5 MeV neutrons

Mg is .063 Barns for Thermal Neutrons.

Which says that if we can get an operational life of the superconductors at 10 hours with ordinary Boron, a year should be possible with five to six nines pure B11.

Reduce the Flux another factor of 10 with water moderation and a B10 absorption layer and you are up to 10 years operation. Double that Boron 10 thickness and you are up to 100 years. Which should allow for various inaccuracies and production variations.

10 B has a Maxwellian thermal neutron flux cross section of almost 4,000 barns.

11 B is around .1 barn.

At room temperature Borax B(OH)3 is soluble at about 57 g/ liter. Which is about 9.3 g/ liter of B10.

Maximum properties of MgB occur at 2E18/cm^2 total neutron flux. Let us say 1E18 and have some safety margin.

Typical fission reactor neutron flux is 1E12/second. Let us say because of the lower energy per reaction a D-D reactor would have 50X that flux.

So that is 20,000 seconds at full power with natural boron. Say 4 1/2 hours. If we go to B11 superconductors assume a 1,000 time improvement. That is 4,500 hours. Say 6 months roughly. So we need a B10 shield that can reduce the neutron flux at the coils by a factor of 10. Giving a life of 5 to 7 years continuous operation.

Since MgB is cheap, replacing the coils every 5 to 10 years should not be a big burden. In addition preconditioned coils capable of sustaining 30 T might get a premium.

Update: 07 Feb 008 0414z

revised thicknesses
I think it is worthwhile to look at the B10 thickness required to absorb 1/10th of the incident thermal neutrons. I calculated it and came up with .005 cm. That is right 5 thousandths of a cm. To slow the neutrons from an average of 2 MeV to .025 eV (thermal energy) requires a thickness of water of about 2 1/4 inches (5.7 cm). About what I would expect to need on the basis of heat transfer and pumping considerations alone. It might be possible to include that B10 thickness (or even 3X that) in the construction of the 300K coolant channel. Just deposit it on the interior since there is no heat transfer consideration (except pumping losses from wall roughness) involved.

At a flux of 1E12 neutrons a second per sq cm., 1 sq cm will have a total flux of 3.16E20 in 10 years. To handle that number of disintegrations would require a thickness of .003 cm. Not too tough. Since the actual density required could be cut in half without seriously affecting the required volume of absorber, it might work out to fill an extra layer with boron powder. That way any break up of "structure" from radiation damage would have little effect on the absorbing properties compared to initial conditions. A layer .1 cm thick could be adequate if you recompressed it from time to time. Certainly a cm or two would be overkill.

I forgot that a D-D reactor with the same thermal power out as a fission nuke will produce about 50X as many neutrons. The 1E12 factor is based on a fission nuke. Still not a show stopper.

Update:

I have a show stopper. Each neutron absorbed produces 2.8 MeV. In a D-D reactor there is no way to carry the heat away without adding more water layers. At best a very thin layer might buy us some operational time for a test reactor. The advantage may go to using a B11 superconductor even with its lower Tc. That still only gets us months of operation. Probably good enough for experimental work.

BTW the neutron flux in a D-D reactor with a coil radius of 2 m at the coil radius is on the order of 3E14 neutrons a second at 100 MW fusion output.

Further Update:

With an intermediate layer filled with borated water to absorb 99% of the neutron energy, or 99.9%, you might get the flux down to where powdered boron could handle the rest. Great idea. At 9.3 g/l that is 9.3E-4 g/cc. Compared to 2 g/cc that would require about 10 cm - vs .005 cm for a factor of 10 reduction. Not going to work. So it still looks like MgB11 superconductors with B11 at 4 nines or better. That still only buys you a total of 1,000 hours - probably enough for initial experimental work at 100 MW.

If you could maintain a slurry of boron particles and still keep the whole contraption cool - it might work.

The trouble is that it almost doubles the neutron thermal load (1.75X). The neutrons lose 3.65 MeV thermalizing and then the B10 adds a 2.8MeV alpha. Which increases the total heat load by about 40% in what was already a marginal situation.

Superconducting Magnet Advances

Here is an interesting paper on recent advances in elevated temperature (20K) superconductors.

We investigated the effect of nanoscale-C doping on the critical current density Jc and irreversibility field Birr of Fe-sheathed MgB2 tapes prepared by the in-situ powder-in-tube method. The tapes were heat treated at 600-950C for 1 h. Higher values of Jc and Birr were seen for 5 at.%C-doped MgB2 tapes at higher sintering temperatures, where substantial substitution of boron for carbon occurred. The C-doped samples sintered at 950C showed the highest Birr, for example, at 4.2 K, the Birr reached 22.9 T. In particular, at 20 K, Birr for the C-doped tape achieved 9 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. This role of nano-sized C particles can be very beneficial in the fabrication of MgB2 tapes for magnetic resonance imaging applications at 20 K.

I sure hope this stuff is available commercially by the time we decide to build WB-100. And think of it. Another good use for Boron.

Considering that we are quite happy (for now) operating at the 1T to 2T range, we might be able to go higher than 20K operation. If higher fields seem useful we can go to lower temperatures.