Building a Miniature Magnetic Earth

Doofus writes "There was an interesting story on NPR this morning about a geophysicist who has constructed a miniature earth to model the earth's dynamo effects. Dan Lathrop, a geophysicist at the University of Maryland, has constructed a 10-foot diameter stainless steel sphere. He intends to fill the sphere with molten sodium and spin the sphere to examine the propensity for the system to generate its own magnetic field. The article includes both video, in which Lathrop spins up the sphere, and audio, including the conversion of magnetic wave functions in prior experiments into audible sound: literally the music of the spheres."

Comments

hold on, fxiing that

[bsDaemon]

I meant to quote all of:

Lathrop figures it can't be too hard to get a magnetic field â" after all, most planets in our solar system have one.

But while nature has an easy time making magnetic fields, scientists do not. This is Lathrop's third attempt. there we go. but the point still remains, yes - he's tried and failed before. Hopefully this time he'll manage it.

any chance

[Trailer Trash]

we can throw it in a lake when he's finished? That's a *lot* of sodium.

Re:thats a lot of sodium...

[hkfczrqj]

Just FYI, one of the technicians working in this experiment used to work in a nuclear submarine, I presume taking care of the cooling of a reactor. I don't know what kind of reactors they use in the Navy, but Dr. Lathrop told me that this guy knows how to handle liquid sodium. (Disclaimer: I'm in a collaboration with Lathrop's lab, though in another experiment.)

Re:thats a lot of sodium...

[Otter]

Just FYI, one of the technicians working in this experiment used to work in a nuclear submarine, I presume taking care of the cooling of a reactor. I don't know what kind of reactors they use in the Navy, but Dr. Lathrop told me that this guy knows how to handle liquid sodium.

The only US sub with such a reactor was the Seawolf in the 1950s. If the tech is Russian -- Alfa's have lead-cooled reactors, not sodium-cooled, IIRC.

Re:Swiss

[bsDaemon]

Its only flat when you cut it, at which point the holes cease to be hollows and are merely holes.

at any rate, the inquisition has marked you... don't say later that you didn't expect it!

Liquid Sodium is still neutral in charge.

[Jerry]

So, how is spinning a neutral liquid metal going to create an electric field?

Are they hoping that rotating Sodium will be like moving a solid piece of Iron through the magnetic field of the earth, inducing current in the Sodium, which then creates a secondary EMF, which then creates a secondary magnetic field...?

Without Earth's magnetic field are they lifting themselves by their own bootstraps?

Re:Liquid Sodium is still neutral in charge.

[Anonymous Coward]

It's not really a stretch to suppose that some "seeding" field was already present.

I wouldn't worry too much about seeding, per se, in that it's possible to build an electric generator without any permanent magnets (or external magnetic field).

With an electric generator, though, one part is moved past another part (by applying forces to both parts). It seems plausible that magnetic fields could be generated if currents of the molten metal were forced to flow past each other (for example, with mixing). It's unclear to me though whether rotating the containment shell would be sufficient to generate flows within the molten metal.

Certainly the flow of the molten metal must be important because otherwise they could just spin a solid metal sphere (and dispense with the molten sodium). On the other hand, unless there are currents of molten metal within the sphere then spinning the molten metal sphere will be equivalent to spinning a solid metal sphere.

With an electric generator force is applied to two different parts of the generator so the electric and magnetic fields are forced to move relative to each other. Presumably one would want the spinning molten metal to move relative to some stationary (non-rotating) fields but I not sure what is supposed to sustain/generate the stationary fields.

I assume that someone has worked through the math (run some computer simulations) and showed that it has a chance to work. A priori, though, it's not at all clear to me that it would work.

That's not to say that they shouldn't try: it looks like a very neat experiment.

Why sodium?

[Fallen Andy]

Anyone out there can explain to me why he wouldn't use e.g. Gallium ? Sodium sure isn't the safest stuff to have around molten.

Andy

Re:solid core?

[DerekLyons]

Don't you need the solid iron core, so that you have the 2 iron pieces separated by the liquid (sodium) mantle ?

Not to study the gross effects of turbulent conductive metal. Simple experiments first, complex experiments later.

Re:Major flaw in design...

[n3umh]

"I'm no geophysicist, but I have a hunch gravity has a huge impact on the equation when it comes to the generation of the Earth's magnetic field."

Only in that the earth's core's flow is driven by convection (both/either thermal and compositional)

The static pressure field in a fluid cancels out gravitational effects, so in our experiment (I'm one of the graduate students who's been building the thing) there's just a slight increase in pressure as you go deeper in the sodium that doesn't change its electrical or hydrodynamic properties at all.

In the earth, buoyancy forces are important to stir up the core. In our experiment, we use differential rotation between a pair of spheres to drive the flow. That aspect is not particularly earthlike, but easier to put a lot of energy in.