World's Strongest Magnet!

This is the world's strongest magnet, capable of sucking objects in and generating electric current. Can you see that? And levitating non-magnetic objects. It even wreaks havoc on camera equipment.

Wire is magnetic!

So if it's a CMOS sensor, the electrons just can't find their way.

Well, they get redirected.

So yeah, if you notice bad video or audio, know that it's incredibly hard to shoot in these magnetic fields. A portion of this video was sponsored by Google. I came to the National High Magnetic Field Laboratory in Tallahassee, Florida, where since the year 2000, they have held the Guinness World Record for the strongest continuous magnetic field.

Somebody left a chair where it wasn't supposed to be. It then got accelerated across the cell, completely pulled the guts out of the chair. Now we all have those nice, super uncomfortable, wooden chairs.

For reference, the magnetic field of the Earth is 0.00005 Tesla. A fridge magnet is around 0.01 Tesla. MRI machines can get up to three Tesla. But this electromagnet creates a magnetic field of 45 Tesla, so nearly a million times Earth's magnetic field. To achieve this field, the magnet consists of an outer superconducting magnet and an inner resistive magnet. I'll explain why you need both types in a moment. The apparatus is two stories tall, but the maximum field, or field center, only occurs in the center of a narrow cylinder that runs through the middle.

Right now it's off.

Is it?

[Tim] There's no magnet.

Can I put my finger in the bore? Is that a bad idea?

No, it's fine. You can totally do that.

I'm gonna see. Oh. So that's where there's 45 Tesla.

Further down. A meter away from that.

A meter down. And so that just drops down for a couple meters?

It's clear all the way through to the bottom.

Oh wow.

The maximum field is basically a centimeter tall.

Yeah.

Here we have very small samples. Think something like a chip in a computer or a cell phone. That's what users will come in with. So that's plenty big for what we want to do with material science or kinetic matter research.

Since we can't see or film in the center of the magnet, we're going to experiment with the magnetic field that extends above and around the magnet on this platform. So the magnet's over there?

Yes.

But the magnetic field extends all the way out here.

Yes.

And past. This is known as the fringe field, and although it's much weaker than 45 Tesla, it is still plenty dangerous.

For a superconducting magnet, it depends on the size of that bore. So the bigger the bore, the larger the fringe field, because the magnetic flux does not penetrate the windings. And you have to form a complete loop. So those loops just move further and further and further out to make that field. So this is the 100 Gauss line for the fringe field.

So what happens to objects around the 100 Gauss line?

Things with shapes will start orienting themselves to the field. So if you have it sitting on a tabletop, say over here, it will start pivoting on its own. And if you get it too much closer, it will just go. And by the time you notice it's moving, it's already too late. Meaning, no ferromagnetic objects within the 100 Gauss line. If you have anything ferromagnetic on you, any implants that are metallic. Pacemaker? Anybody? Anybody? Anybody? Okay.

Ramping up this magnet to full power takes around an hour and a half. That's because they have to put 47,000 amps of current into the outer superconducting electromagnet. 47,000 amps.

47,000 amps, 500 volts.

It is so insane.

[Tim] All right, so let's take it all the way up to full field.

One thing that happens in a strong magnetic field, obviously, is that magnetic materials are attracted to it. We cut open a Nerf football and put in a couple steel washers being careful to tape it up so the washers can't get out. We also covered the opening to the magnet so the ball won't get sucked down into it. I got an unmodified Nerf football. And sure enough, it's easy to tell which ball contains the washers. I tried to throw the football and hit the side of the magnet. Okay. After a few misses. No! Are you kidding me? No.

No.

It bounced around and stuck. It should have looked more like this. Another thing to do if you have a strong magnet is get ferrofluid fluid. Ferrofluid fluid contains nanoscale pieces of magnetite, that's an iron containing mineral, and they're suspended in solution coded in surfactants so they don't all clump together. But in an external magnetic field, they all line up like iron filings around a bar magnet. This ferrofluid fluid started to develop parallel ridges even meters away from the magnet. And as we got closer, spikes formed on the surface, aligning the magnetite particles with the field. Closer still and the ferrofluid fluid climbed up the side of the vessel.

[Tim] So it's not much, but it's just kind of a.

A little bit of a tug?

[Tim] Yep, and then try and tilt it away, and then you'll feel the difference.

Oh yeah. It definitely preferentially wants to come this way. Magnetite is actually the mineral that led people to discover the phenomenon of magnetism in the first place. At least 3000 years ago, naturally magnetized pieces of magnetite were found in a part of Greece called Magnesia. That's actually where the word magnet comes from. In Greek, they were called stones from magnesia but they were also referred to as lodestones. And it was discovered that lodestones could attract each other or pieces of iron. And by the 11th century in China, it was realized that magnets could be used to make a compass needle that would always point in the same direction. The side that pointed to the north of the earth was referred to as a north seeking pole. And the other side, the south seeking pole. Though these days we often just say North Pole and South Pole of the magnet.

But why are only some materials magnetic? Electrons are essentially tiny magnets, but in most atoms, they are paired up, one pointing one way and the other pointing the opposite way. So their fields cancel out. In elements with half full outer shells of electrons, well, then they can't pair up. So atoms have magnetic fields. But if neighboring atoms aren't aligned, well then, the magnetic fields of all the atoms cancel out and the bulk material is non-magnetic. But even if you get all these atoms aligning in one part of the material, known as a domain, they may be aligned opposite atoms in other domains and cancel out. So you need all the domains to be aligned.

Normally when you see these, they're really strong magnets. But not here and not yet. And this can be done by applying a strong external magnetic field. So right now, these are not magnetic. They do not stick to each other. But he is loading them in there, into the Helmholtz coil.

See the machine here?

Whoa! And then you get a permanent magnet. Materials that meet these criteria are called ferromagnetic. After iron, the most common magnetic element. But nickel and cobalt are also ferromagnetic magnetic. In the powerful magnetic field around the world's strongest magnet, what is even more surprising to see is the behavior of non-ferromagnetic materials. Here we have four sheets of different materials. Two different types of plastic, copper, and aluminum. When they are stationary in the field, there's no difference between them. But when they move.

Two, one, drop!

Materials that conduct electricity fall a lot slower.

(gentle upbeat music)

I'll get into that. But first, this portion of the video was sponsored by Google and they were interested in this video because it's all about magnets, which are core to our future. Electric vehicles, for example, use electric motors, which need magnets to work. And US search interest for electric vehicle reached an all-time high in the last 12 months. That is, according to Google Trends, a tool that allows you to see what people are searching for. The thing that connects these trending searches and many others, is that people are trying to find ways of doing things that are less destructive to the planet. And Google is like, "We live on this planet too. We also wanna do that."

In fact, Google has matched 100% of their electricity use with renewable energy since 2017. They also run Project Sunroof, which helps people decide if solar is right for their home by providing Google Maps data to create a 3D model of your roof and estimate energy savings from rooftop solar. Personally, I'm just happy to learn that people are searching for things related to sustainability and that Google has made a real commitment to sustainability, too. You can learn more about sustainability and Google's efforts at sustainability.google. So thanks to Google for sponsoring that part of my video.

And now, back to magnets. What's happening is that, as the metal plate is falling through the field, the number of magnetic field lines passing through it is changing. This change in magnetic flux induces electric currents, called eddy currents in the plate, which create their own magnetic field that opposes the change in the flux. This is known as Lenz's Law. So if the plate is falling towards a north magnetic pole, the induced currents create a north magnetic pole themselves so that the plate is repelled and so it falls much slower. So as that big plate falls, there are eddy currents generated in the metal, which should dissipate some energy as heat. So I wanna see if we can see that.

[Tim] It's actually slowing down now. 'Cause it's in a much higher field.

Now it is slight, but I think you can see that the plate is warming up a bit as it falls. Previously, I visited an electromagnetic levitator at the Palace of Discovery in Paris. Whoa! It uses an alternating current to levitate a plate, but the eddy currents in that plate generate so much heat that water actually boils on its surface. Check out how hot this plate is. I like to think of Lenz's Law as the "No You Don't" Law because whatever you try to do, nature acts to oppose you.

There you go.

Ah! If the plate is falling, eddy currents are induced to slow its dissent. Look at it! (laughs) But if you try to pick up the plate. (laughs) Come on! Nature also says, "No, you don't." In this case, a south magnetic pole is induced under the plate, attracting it back to the magnet. They don't know if I'm weak or if this is actually insanely difficult. Ah, ah. Oh.

There you go.

Oh my goodness.

You're strong like bull.

Whoa. No matter how hard I tried to push the plate down, it just wouldn't go very fast. Because even if I could speed it up a little bit, that would increase the rate of change of flux, and hence the induced currents and their associated magnetic field. That is ridiculous. It's so weird.

We tried a number of other conductive, but non-magnetic objects, around the magnet, like this thick cylinder of aluminum. Drop it straight on the magnet and nature says, "No you don't." Try to roll it across the top. No you don't. It just refuses to roll. We wrapped up a volleyball in aluminum foil and passed it across the magnet. Or dropped it straight in. Again, the changing magnetic flux induces eddy currents that produce their own magnetic field to oppose the original change in flux.

We wanted to see just how much deceleration the fringe field of the 45 Tesla magnet could achieve. So we decided to fire projectiles from a potato cannon across the top.

You ready?

All right, we're ready.

Three, two, one. (metal clanks) Heads! (metal clanks)

This is what the projectile looked like with the magnetic field off. And this is what it looked like with the magnetic field on. If we compare the two shots, you can see that as the projectile enters the magnetic field, the induced eddy currents rotate the projectile. So it remains oriented along the magnetic field lines.

[Operator] Three, two, one.

Now, some of the projectiles contained coils of wire that were connected to LEDs.

So the LEDs are actually biased opposite polarity. So no matter which direction the field is coming in, one of them will be lit. And we're hoping that as it crosses through a field, you'll see the change in color of LED of the nose cone.

Mar And sure enough, these projectiles light up, showing how the induced currents are changing in the coil.

(gentle music)

You know, in all these cases the induced electric energy is dissipated, either as light or heat. But what if you had a material that didn't dissipate energy, like a superconductor below its critical temperature? There are two important things to know about the high temperature superconductor we're using here. First, below its critical temperature, most of the material has zero electrical resistance, which means, if you bring a magnet close to it, currents will be induced to oppose the change in flux. And since it's a superconductor, those currents can persist indefinitely and expel all of the magnetic field.

Second, there are some filaments through the material that are not superconducting.

There's defects that are engineered into the superconductors, a second phase that traps those magnetic field lines and keeps them from moving. It can no longer rise or fall because it's kind of locked in that magnetic configuration.

This is the human levitator. It consists of a 90 pound, or 40 kilogram, magnet, hovering above a ring of superconductors. So I'm standing at the magnet, and underneath is the superconductor?

That's right.

When I stand on the magnet, it is pressed down into the superconductors. But the increase in magnetic flux is opposed by currents in the superconductors creating a magnetic field that repels the magnetic field from the magnet I'm standing on. Maintain my angular moment.

Oh yeah. So I remain levitating above the superconductors.

[Speaker] I also brought a leaf blower, if you wanna hold on that, turn it on.

For real? (group laughs)

It's up to you.

Let's get it. (leaf blower whirs)

Now, there's another way to levitate in a magnetic field that has nothing to do with induced eddy currents. And it's all because all materials actually have magnetic properties. They're just hard to see unless a strong magnetic field is present. Some materials are always attracted to magnetic fields. They display what's called paramagnetism. Oxygen is like this.

We have liquid oxygen dripping off the bottom here, and it gets attracted to the magnet. It doesn't matter if it's a north or south magnetic pole, the presence of the external field causes the magnetic field of material to strengthen the overall magnetic field. And that causes attraction.

Other materials, in fact, most materials are repelled by a strong enough magnetic field, either north or south. And this is known as diamagnetism. Water is a good example of this. In the presence of the external field, the water molecules become opposing magnets effectively. And so they are repelled.

So here you can see how bringing a magnet close to the surface of water creates an indent. You can use this repulsion in a strong enough magnetic field to levitate objects you ordinarily wouldn't think of as magnetic. Here we're using a slightly weaker 31 Tesla magnet so that we can use a periscope setup to actually see into the bore. And our camera is there.

So as soon as you are on this optical way, you should be able to put everything down.

Wonderful. This strawberry will be magnetic in a strong enough field.

Well, it's diamagnetic right now. It's just we're not in a strong enough field.

Right.

Yeah.

For us to see anything.

Mm hmm. Correct. Because of the water.

Right.

Water is diamagnetic and there's a lot of water in strawberries.

Oh, that's nice. Oh, that's beautiful. Yeah, it's beautiful. And the same occurs with a raspberry or a little piece of plastic pizza. Living organisms contain enough water that they too can be levitated. They wouldn't do it here at the mag lab but people have levitated frogs.

Oh!

Yep, this is it! Yep, there you go.

No way!

And grasshoppers? Even mice in experiments meant to help understand the effects of weightlessness without having to go into space.

So are very strong magnetic fields safe for living things?

There are no lasting effects, there are no long-term effects. But we have noticed that there is the possibility of actually polarizing the stones that are in the inner ear. And the effect that that has on the rodent is that the rodent actually spins.

Like they go in circles?

They go in circles. It doesn't last for very long. It's only a few minutes after the animal comes out of the magnet.

So how do you actually make the world's strongest magnet? Contrary to what I expected, you can't do it just with superconducting magnets alone.

The highest magnetic field you could generate with superconducting wire was nominally 20 Tesla.

That's because superconductors have a limit to the amount of magnetic field they can withstand before they're no longer superconducting. So the solution is to combine an outer superconducting electromagnet with an inner electromagnet made of ordinary wire.

So the blue, green, and salmon colored bits, that's the superconducting outsert. That produces 11.5 Tesla. Inside of that, we put a resistive magnet that produces 33 and a half Tesla. Maxwell's equations, fields add, we get 45 Tesla.

But making high field magnets with ordinary resistive wire is really hard.

For a wire wound magnet, like a junkyard magnet, a traditional electromagnet, the highest magnetic field you can get is about two Tesla. And the reason is that you cannot get the heat out of the innermost windings.

So back in the 1950s, Francis Bitter, up at MIT, he realized that physics doesn't care what shape the conductor is. You can take your round wire and smash it into a very thin plate. If you then stack those plates with alternating insulators, you make a helix, that electrically looks just like that. But now I can push cooling water axially through the stack of conductor. So that means that innermost part, I can now pull all that heat away, which means I can go to much, much, much, much, much higher currents through these coils up to 57,000 amps than what you can do with a traditional wire round electromagnet.

And that gives you 34 Tesla, that?

That gives you 33.5, but it's stacked up. So we stack all of these up in a stacking jig. They're aligned up with tie rods. We then put about 20 tons of force on it and then lock those tie rods down and that holds the coil together and it gives us our electrical connection between each turn. And we're pushing, you know, several thousand gallons per minute of deionized water through those coils to keep them cold 'cause otherwise it melts and you're done.

Occasionally you get material failure that happens when the material goes past its plastic limit and starts flexing either into the coil next to it or maybe even shorting to ground. And this is what happened here.

The coil plastically failed, meaning the metal went beyond its springy characteristics, where it would come back, and it just completely deformed, which drove it into the coil next to it, burned through the insulator, and then vaporized all of this metal. And you can see more on the inside. It killed this coil, which is the B coil. But because it failed on the inner edge, it killed the A coil. Failed on the outer edge, it also killed the C coil. So that was an expensive failure.

Expensive failure.

Yeah. Yeah. The record is the highest continuous magnetic field in the world, period. China recently commissioned their 45 Tesla hybrid, very similar in concept to ours. So now there's two of them in the world.

Running the strongest magnets on the planet takes a lot of energy. The Mag Lab uses a significant fraction of Tallahassee's electricity.

So we can consume with all four power supplies at full blast about 8% of their total generating capacity.

What's the electricity budget of this place?

So nominal $250 to $300,000 a month.

Holy, yeah, that's a lot.

Yeah. So we operate in their federally mandated reserve, which every utility has to have. They have to have that available to push into the grid if there's a problem. We have a deal set up with the city so that they can actually make money off that power that they have to produce, but which they can't sell. The flip side is, when they need it, we ramp down, and we can go down much faster than they can spin up a Genny.

Why do you need 45 Tesla?

There are a couple things that drive material discovery. One of them is just growing a new material. The other one is putting it in an extreme environment, like high magnetic field, high electric field, high pressure, ultra-low temperature.

Low temperature.

Another axis is taking an existing material and improving its cleanliness. So getting all the impurities out. So as you drop the impurities in the material, you're reducing where the electrons scatter from in there. And that improves the properties, enables you to see things that you were never able to see before. We've only just barely scratched the surface on what can be done with this. People are gonna look back about 25 years from now and this will be the inflection point, this five year period.