Wisconsin Public Television University Place  Solar Astrophysics in the Lab  David Weisberg  5/14/13 UP876  cc >> Welcome to Space Place tonight. This one of our guest presentations. Tonight our guest is Dave Weisberg from the UW Physics Department. He is a grad student and researcher in the department. He works on the Madison Plasma Dynamo experiment, which seeks to answer, among other things, the questions about how magnetic fields form in space. Dave's talk tonight is How the Sun Got its Spots. He's going to tell us tonight about the experimental work and solar plasma physics. And probably about some other things too. Dave, thanks for coming tonight. >> Thanks, Jim. 

[applause] Thanks all for coming tonight. Hopefully by the end of our hour together I'll have convinced you a little bit of why what we're doing in our lab is important and interesting. Hopefully you'll have learned something about the physics behind the research we're doing. Like Jim said, I'm from the Department of Physics, specifically the plasma group in the Department of Physics. We'll talk about what plasma is and how we work with it in the laboratory. I guess I should say that our work is sponsored by the NSF and also by the Center for Magnetic Self-organization, which is a group funded by the NSF. Laboratory astrophysics is what I do. It's kind of worth taking a moment to look at this term because it takes two different words that really aren't easily combined. Astrophysics is the study of big things, the study of space. More specifically, it's the study of the physics of space. 

It's more than just looking at stars with telescopes. It's figuring out what makes stars work on the physics level. That involves huge scales. Laboratory implies that you're doing it in a room with equipment and a very small scale. Combining these two things is really hard in practice. You need to make what you're doing in the laboratory apply to these huge scales. You need the physics results you find in the lab to mimic what we think is happening on these huge, light year scales. That's always hard to do. As an example, this is the sun. It's a huge star, our star. 

It's gigantic. This is the experiment we have that we're trying to use to explore what physics goes on inside the sun. The sun is millions of times bigger than the Earth as far as volume goes. Our experiment is about ten feet in diameter. Using our experiment to get results, and then convince people that those results apply to the sun, is a hard thing to do. I'll try to explain why that is as we go on. Of course, the sun in a laboratory is an exciting idea. Maybe some of you saw Spiderman II. The evil guy is Spiderman II tries to make a sun in the laboratory and it blows up, and everything goes wrong. That's not what we're trying to do. 

What we're trying to do is much more subtle. It's not as grandiose as this. The sun is really, really complicated. It's huge. It has all these different parts of it, different length scales. We're just trying to explore very, very simple version of one type of physics going on in the sun. The question we're trying to answer in its most basic level is why our magnetic fields so common in the universe. Some of you might say, I didn't know magnetic fields were common in the universe. And that's totally understandable. We're really only familiar with one magnetic field, that's the Earth's magnetic field. 

We might not interact with it everyday, but things we use so, GPS devices, compasses, obviously. So it's worth starting with the Earth and kind of building up from there. Just to kind of refresh in your minds what a magnetic field is we'll start with something really simple, a bar magnet. I'm sure all of you have seen these at one time or another. It has a north pole and a south pole just like the Earth. We describe the magnetic field of a bar magnet using lines. You can kind of see them here. This is a piece of paper covered in iron filings. You put the bar magnet on the iron filings and they align themselves with the field lines. This picture here is just a diagram of what those field lines would look like. 

You can see, they kind of resemble each other. So the field lines describe the magnetic shape. They come out of the north pole and go back into the south pole. When you look at the Earth which has a north pole and a south pole, you see something very similar. You have field lines going from one pole into the other. Everything in a magnetic field, if it's metal for example, will try to align itself with that magnetic field. Specifically, if you have a compass on the Earth it will-- It's a magnetized piece of metal, a magnetized needle. It will try to align itself so that it's parallel to the magnetic field lines. That's why you can get a compass to point north, or south if you magnetize it the other direction. Really, they're kind of interchangeable. 

You just have a straight line. Now the Earth has a magnetic field. It's really strong. And it's really, really good that the Earth has a magnetic field, because it does a lot for us. Other than letting us navigate, it protects us from space weather. The sun, our closest star, is really violent. It's constantly spitting off particles, light and all different types of energy. Our magnetic field deflects that energy around our Earth which prevents us from receiving all this harmful radiation, which can cause cancer, and probably would stop life from forming in the first place. So the Earth's magnetic field is very nice to have. A really interesting thing about the Earth's magnetic field is that it changes. 

It's not something that's constant. This diagram kind of shows measurements of the magnetic north pole. First of all, the magnetic north pole isn't the same as the geographic north pole. The geographic north pole is at the top of the Earth. It's at the top of the rotation axis of the Earth. The magnetic north pole is close, but it's not exactly on it. You can see, here from the 1800's to very recently, it moves. It's kind of tracking northward, this is northern Canada, towards the geographic north pole. The magnetic field of the Earth changes on this 200 year scale. It also changes on an even longer scale. 

Every 100,000 years or so the polarity of the Earth's magnetic field will flip. What was once the north pole will become the south pole over a period of, maybe, I don't know-- I don't want to say because I'm not sure. But over a much shorter period than that longer period of stability. We know that from geographic records, historical records. We have evidence that the Earth's magnetic field is not a stable thing. It's very dynamic. It's changing all the time. This is a really good hint as to how magnetic fields in planets arise in the first place. This is a cool video. It turns out that mariners, sailors, for the past 400 years, have been navigating the oceans using the Earth's magnetic field. 

They have compasses on board, very precise compasses, that measure the magnetic field in all three dimensions. By doing that we have records of the magnetic field that go back 400 years. What I'm about to show you is a movie of, basically, the Earth's magnetic field if you took away the north/south component. That's the biggest component, but if you took it away, you see there's a lot finer structure of the Earth's magnetic field. This is a magnetic field kind of in the up/down direction. Red is up. Blue is down. You can see it changes over time. The top number is 1780. Every increment is two years. 

You can see, this field is small. A smaller structured field is very dynamic as well. It's not steady either. So more evidence that the Earth's magnetic field isn't a stationary thing. It's constantly changing. It's also really neat that we can use something like this today in physics even though this is data from 1630 and onwards. I find that really cool. All right, that's the Earth's magnetic field. Let's move on to the next most important field to us. That's our sun's magnetic field. 

The sun has a magnetic field. Unlike the Earth's magnetic field, it's not dipolar primarily. It doesn't have a north pole and a south pole. The strongest component of the sun's magnetic field is more like that fine grained movie I just showed you where there are many, kind of, spots on the sun that have different directions of magnetic field. We also know that the magnetic field of the sun isn't steady either. It changes. And it changes much faster than the Earth's magnetic field. These are two pictures of the sun from 2001 and 2005. You can see in one there are lots of sunspots, because the sun has spots. The caveat is, sometimes, because four years later, there are no sunspots on the sun. 

If you've been reading news about the sun recently you'll know that right now the sun is in another phase where there are lots of sunspots on the sun. What scientists have discovered is that sunspots indicate strong magnetic field activity on the face of the sun. This is the same as saying in 2001 there was a lot of magnetic activity in the sun, and in 2005 there was a very low amount of magnetic activity in the sun. Today now there is another peak in the magnetic activity. So the sun has this 11 year cycle. As I said, you can see sunspots are a proxy for the magnetic field. You can also see these sparks that come out of the sun. These are called solar prominences. What this really is is a magnetic field line that pokes it way through the surface of the sun. Here's the start of it, the it curls its way back into the sun. 

The sun's material follows along that field line. This is visually the magnetic field of the sun. These structures are very short lived, on the order of months, at longest a year. Eventually they build up energy and explode into what you may have heard called coronal mass ejections. Those spew all this material out into the solar system, and are very interesting to people that follow space weather. One thing I haven't told you is why sunspots indicate magnetic field strength. The answer to that is each sunspot is literally a magnetic field line coming out of the surface of the sun or going into the surface of the sun. For that reason, sunspots occur in pairs usually. You have a magnetic field coming out here and going in here. Just like in this picture except from a bird's-eye view. 

Yeah. >> Is that a real picture? >> These are real pictures, yeah. These aren't artist's simulations. We have an array of satellites orbiting the sun taking picture 24/7, recording all the different activities that go on on the face of the sun. Sunspots, as they're magnetic field coming out from the surface of the sun, the material of the sun cools down. The magnetic energy kind of repels all the hot material. That's why these sunspots are dark, because they're cooler than the rest of the surface of the sun. This is a cool video showing the sunspot activity on the face of the sun. The different colors indicate the different of the magnetic field. Blue is a magnetic field coming out of the sun. 

Yellow is a magnetic field going into the sun. You can see they're kind of paired. I'll play this for you. As you watch it, this is kind of sped up over a series of, well, maybe like a year a second. It's a look at the sun as far as longitude in the X direction, and latitude in the Y direction. As time progresses, you can see the sunspot kind of disappear, there's a quiet phase, then the sunspots come roaring back. Then they disappear again. If you are really observant you'd notice that they're starting far away from the equator and they're moving closer to the equator as time progresses. All these things tell us about the magnetic field of the sun. We can take kind of a snapshot of this. 

You can see that trend I just talked about start in moving away from the equator and moving towards the equator. Here we have and averaged indication on the sunspot activity as a function of latitude. So here's the north pole, here's the equator, here's the south pole, and here's time. So you can see over time we have these regions of intense sunspot activity, then there's a low point. And then the sunspots come back, and there's a low point. This cycle is 11 years. This diagram is pretty famously called the butterfly diagram, because, I mean, it looks like a bunch of butterflies. Again, we have data going back quite a ways to the mid-1800's. People have been looking at the sun for a long time. You can see that this periodicity is really even. 

What we just saw, these periods right here, correspond to these three butterflies right here. Basically, what I'm trying to get at is that, the magnetic fields we're familiar with, the Earth's field and the sun's field, change all the time. And we don't know why per se. That's what we're trying to figure out. Just kind of in passing, it's really neat to think about the fact that there are magnetic fields on even bigger scales. Galaxies have coherent magnetic field structures. By that I mean, there is a pattern to the magnetic field of a galaxy if you look at it as a whole structure. This is galaxy M51. It's face onto us. If you use special observation techniques you can deduce the direction of the magnetic field. 

I know these arrows are hard to see, but the point is, they follow the spiral arms of the galaxy. The magnetic field of the galaxy mimics the structure that you see. This is another picture of another galaxy that we see edge on. Again, the lines are hard to see, but there's an X shape crossing through the center of the galaxy. The magnetic field extends above and below the galaxy, in again, a structured pattern. Finally, on the biggest scales, galaxy clusters have magnetic fields. A galaxy cluster is a group of hundreds of thousands of galaxies orbiting together, attracted to each other, gravitationally. In this picture you can see there are two darker spots in this otherwise bright center. I've kind of circled them. It's theorized that these spots are regions of high magnetic field strength. 

Just like on the sun, the magnetic fields here push away hot material so you're left with colder spots. Just to give you a sense of this, 60,000 light years is about as big as a galaxy. This is just the center of the galaxy cluster, and it's many times bigger than the galaxy we saw previously. So we see all this evidence of magnetic fields in the universe, and dynamic magnetic fields in the universe. The question is, why? There are two theories. The first one is, maybe these fields were created at the very beginning of the universe, or at the very beginning of our galaxy, or maybe at the beginning of our solar system. They were created in a short time and they've just stuck around. They're just kind of called relic magnetic fields. They're like digging up fossils and you knew they were created a long time ago, and now they're still here because there's nothing that has been done to destroy them. That's one theory. 

The other theory is that magnetic fields are constantly being maintained by some sort of changing ongoing process. The point is that magnetic fields without this process would disappear pretty quickly compared to the lifetime of the Earth or the sun. There's some physics going on in the Earth or the sun that keeps that magnetic field strong, keeps it from decaying away. That's called dynamo theory. As you've probably already guessed by the name of my experiment, this is the theory that is commonly accepted in the astrophysical community, and this is the theory we're trying to observe in the laboratory. All right, so I'll quickly go over the basics of dynamo theory. I'll try to keep it as intuitive as possible with as few equations as possible. But if I really make a big jump you didn't get, feel free to stop me. I'll go back and go over it again. Dynamo theory started with Michael Faraday in the early 1800's. 

He invented what is called the Faraday generator. It is the first of the whole series of electric generators that have, basically, revolutionized modern industry. This is the very first, and what it was, this is a disk of copper and you spun it. This is one side of a magnet. The other side of the magnet is on the other side. So there's a magnetic field going through the disk. Dynamo theory says, if you have a moving, conducting medium then you can generate a magnetic field. Faraday saw that when he spun this disk in the presence of a magnetic field he observed a growth in that magnetic field. The magnetic field got stronger. In this case the moving, conducting medium was the copper disk. 

Copper is a metal that conducts electricity very well, and he was spinning it, so it was moving. This whole dynamo theory is what allows us to have hydro-electric dams. The moving water spins a turbine, and the motion of the turbine generates electro-magnetic energy that we store and use as power. Dynamo theory basically relies on a positive feedback process. That means that one thing makes another thing grow bigger, A make B grow bigger. But B in turn, make A grow bigger. And so they go back and forth making each other bigger and bigger, and the positive feedback makes them both very large. The first point is that a moving charge will generate a local magnetic field. This is a fundamental point of electro-dynamics in physics. We observe it, we use it, in electro-magnets. 

This is a picture of a crane in a junkyard and there's an electro-magnet that is magnetically attracting all this scrap metal. In order to make an electro-magnet all you have to do take a wire and wind it in a coil, and then run current through the wire. These black lines show the magnetic field lines. You have a south pole and you have a north pole. You can attract scrap metal to your electro-magnet. In this case the moving charge is a current passing through this wire. The second point that you need to know is a moving charge in the presence of a magnetic field will feel a force. This is what's called the Lorentz force. It uses probably every physics student's favorite test-taking tool, the right-hand rule. I don't know how many of you know about the right-hand rule, but it's a way of doing physics when you have what's called a cross product. 

This equation, and I promise this is the only equation I'll have in my talk, this is the equation for the Lorentz force. F is the force. Q is the value of the charge. V is the velocity, and B is the magnetic field. And this X stands for a cross product. We say, F is equal to QV cross B. What that means is that V has a direction, this red line. B has a direction, this blue line. And F has a direction at a right angle to both. The way you do this if you're taking your final in physics class and you've forgotten everything is, you use your right hand. 

You point in the direction of the first thing, which in this case is V. You stick your middle finger in the direction of the second vector, which is B. And then your thumb gives you the direction of F. So if you ever forget about the cross product the right-hand rule is a great way to remember it. These two things combined mean that the magnetic field, in the proper system, will grow exponentially. Exponentially means really, really fast. The rate of growth increases as time goes on. So it grows super-fast. The simplest example of dynamo theory is what's called a homopolar dynamo. What this is, it's a copper disk just like Faraday's dynamo, and it's rotating around this axis. 

It has a wire connecting the axis to the edge of the disk, and the wire loops in this way. If we were to pick a point on the disk we can figure out what way the magnetic field goes if there's a current. So just like an electro-magnet, if you have a magnetic field going in the counter-clockwise direction, then you have a magnetic field pointing up, just like these arrows. B stands for the magnetic field. Then you can take into account the rotation of the copper disk which is this green arrow, right? If you were on the copper disk and you let go, you would go in that direction. Then using the right hand rule you can figure out that the force that charge will feel is outward, is radically outwards, from the center of the rotation. What this does is it pushes the current down this wire, pushes the current from the center, the axis of rotation, out to the edge. What's at the edge? This wire. So the current goes down this wire and goes around this loop just like we started with. That is a perfect example of positive feedback. 

You have the current making this magnetic field which, in turn, pushes more current in the same direction, which in turn, makes more magnetic field, which pushes more current, etc, etc. This will result in a big growth in the magnetic field. In reality, others things come into play when you have this particular thing, otherwise I would love to have a physical example of it for you here. But things like friction and other caveats some into play and slow it down before it becomes a good thing to demonstrate. But it's a great way to think about it. It's a great thought problem. All right, so let's go back to space. In space we have lots of conductors. The thing is, they're not solid, at least not the ones we care about. They're liquid. 

A great example is the Earth's outer core. Here's a cutaway of the Earth. The outer core is red here. The inner core is this bright yellow. Even though they're made of basically the same stuff, iron and nickel, the pressure of the outer core is low enough that it can be fluid. It can be a liquid metal. This liquid metal spins with the Earth just like the disk from the previous slide. And on top of that it has all these very complicated vortices and different flows. Geophysicists are trying very hard to simulate these on computers and try to recreate the magnetic field we believe is generated by the flows in this liquid core. Another great example in our solar system is Jupiter. 

In this case, Jupiter is a gas giant. It's much bigger than the Earth. In the center there's thought to be a rocky core, but this big beige area is liquid metallic hydrogen. This such an exotic material, I mean, I couldn't describe it to you. No one's ever made it on Earth I don't think. It requires enormous temperatures and pressures. But the point is, it conducts electricity just like liquid metal. And it's liquid so it has flows as well. It's thought that this liquid metallic hydrogen core generates Jupiter's magnetic field which is the strongest terrestrial magnetic field in the solar system. But yeah, astronomically huge temperatures. 

Here's a diagram of Jupiter's magnetic field with Io, the volcanic moon picked out there. There's a lot of cool stuff going on with Io because it's so volcanic and small. All the volcanoes that shoot up debris, it's kind of not trapped by Io's gravity. It just escapes into the space around Io. Since the stuff that shoots out of the volcanoes is charged it interacts with Jupiter's magnetic field. We'll get to that a little bit later. There's a lot of interesting physics going on with Io and Jupiter. The opposite in our solar system is also true and evident on the planet Mars. Mars doesn't have a magnetic field. Here's a plot of the surface magnetic field of Mars. 

You can see it's really spotty, it's not very strong. It is strong in places but it doesn't have an overall dipole field like Earth. It doesn't have a north or a south pole. It's thought for this reason that this is why Mars doesn't have an atmosphere. The solar wind, all the stuff the sun pukes out and sends flying outward into the solar system, if there's no magnetic field to protect the planet it will rip away the atmosphere very quickly. We're lucky, we have a magnetic field. Our atmosphere is safe, but Mars doesn't. Even though Mars may have been like Earth ions ago, it's magnetic field turned off somehow. It's atmosphere was ripped away and it's now a dead planet. But we still get to send cool robots there like Curiosity, NASA's latest rover. 

Now we can get back to the sun, which has the strongest magnetic field in our solar system. We'll kind of get to the basis of our research. If anyone is into odd music, They Might Be Giants is still a popular band but it was more popular back in the early '90s. They had a song called Why Does The Sun Shine? The chorus goes, "The sun is a mass of incandescent gas." It was kind of a mini-hit back then. Unfortunately, it was wrong. The sun is not a mass of incandescent gas. Recently, in '08, they came out with another song called, Why Does The Sun Really Shine? and the chorus of that goes, "The sun is a miasma of incandescent plasma." [laughter] Which is a great segue into what I'm going to talk about next, because plasma is what we're all about in our lab. It's true, the sun is a miasma of incandescent plasma. The difference is pretty easy actually. Plasma, if you've heard of it-- Not blood plasma, right? That's for biologists. 

This is physics plasma. It's the fourth state of matter. By that I mean it's different from solids, liquids and gases. A good way to describe this is, let's imagine a microwave like you'd have in your kitchen. A reason this is a good way to describe it is because people in laboratories make plasmas using microwaves. They're very, very powerful microwaves, but the principles are the same. Let's say you take ice and you put it in your microwave. Ice is a solid. Here's a picture of a bunch of water molecules locked in an ice crystal form. These bonds between the molecules, these intermolecular bonds are what make ice a solid. 

It holds it's shape. It's hard compared to liquids. If you add enough energy in your microwave you can break these molecular bonds. Now you have a bunch of individual water molecules bouncing about. They still interact, weakly, because their hydrogen and oxygen atoms still kind of attract each other a little bit. But it's a lot more fluid than a solid. If you add more energy then you can first turn it into a gas, water vapor, and then you can turn it into atomic gas. You can rip the hydrogen and the oxygen apart. You'll destroy the intra molecular bonds. Now you just have oxygen and hydrogen in their gaseous form. 

Those are the three state of matter that are most common. But if you add more energy to the gas. You just keep pumping in energy. Then we make plasma. So plasma is what happens when you take an atom and you have enough energy to rip apart the inter atomic bonds. Most all atoms have a positive nucleus with negative ions orbiting it. Plasmas are gases that have had their electrons ripped out of those orbits. Instead of a bunch of atoms flying around, now we have a bunch of electrons and a bunch of ions. Here you can see, this electron coming in has a lot of energy. It hits this atom, and the atom kicks off electrons. 

What's left has a positive charge and the electrons have a negative charge. This is what's called an ionization cascade. For ionization you ionize an atom to make an ion an electron.  The reason why plasmas are so interesting is because now we have a gaseous-like substance that can interact with electric and magnetic fields. It's a bunch of things with charge, so if you take-- Well, for example, if you rub your head on a balloon it builds up static charge. If you hold that in a plasma it will attract the plasma particles with the opposite charge and repel the particles with same charge. This opens up a whole new door to the physics that goes on inside a plasma. Well, you might be asking, how much energy do you need to add in order to make this transition into the fourth state of matter? And the answer is, a lot. Plasma is without a doubt the hottest ordinary stuff in the universe. It's so hot we measure it in terms of electron volts. 

eV is an electron volt, and it's equal to 11,600 degrees Celsius, or if you're American like us, 20,400 degrees Fahrenheit. This is super, super hot. Here's some examples of the temperatures of different plasmas in the universe. Fusion plasma experiments, like there's one in the physics department here called the Madison Symmetric Torus, have extremely hot plasma temperatures, 15keV. The k stands for a thousand. That means 15,000 electron volts. You do the math, 15,000 times 20,000. It's enormous. The center of the sun is 1.3 thousand. It's actually cooler than lots of fusion plasma experiments, but still hot enough to be a fusion generator itself and create heat. 

The surface of the sun is a lot cooler. It's 1.5 electron volts, 1.3 thousand compared to 1.5. But this is still 6,000 degrees. It's still very hot. In comparison, our experiment, the Madison Plasma Dynamo experiment, MPDX for short, has made plasmas of about 10eV. Extremely hot. Probably the hottest the inside of Sterling Hall has ever been. We're pretty proud of that. The reason that we can make these plasmas that are so hot is that we're very good at stopping them from losing their heat to other things. I'll tell you how we do that. 

But first let's finish talking about the sun. Like I said, the center of the sun is hot enough so that nuclear fusion is a favorable process. Basically, the sun glows because different forms of hydrogen come together in the center of the sun with so much energy that they bond and undergo and nuclear reaction. Then they create all this energy that radiates outward through the sun and then hits our Earth in the form of light and heat. This is just a diagram of the sun. You have the hot core. You have a radiative zone where light just kind of bounces around for awhile. Then you have a conductive zone where a more fluid-like material that has lots of complex flows and vortices and counter-propagating streams of fluid. This is where all the dynamo action is thought to occur because, again, it's conductive because it's a plasma, and it's moving in very complicated ways. Plasma is really interesting to study because it's basically everything. 

If you don't talk about dark energy or dark matter, which we don't because that stuff's too hard, everything else, the "ordinary" matter, stuff that you can touch and see and we're familiar with, 99% of that is plasma. That's because all the stars in the universe are made of plasma. All the stuff between the stars, all the very tenuous, defuse gases between the stars are plasma. The only stuff that's not plasma are the planets and comets and asteroids. Next to all the stars, that's virtually nothing. Even in the solar system, the sun is 99.9% of the mass in the solar system. All right, on to the experiments. There are two types of plasma experiments in the laboratory. The first one I already mentioned, briefly, are fusion experiments. They're trying to, in a way, replicate what's going on in the center of the sun. 

They're trying to use plasma as a means of making a power plant. We already have fission power plants, where we take uranium and we split it, and that releases tons of energy. The opposite is fusion, where you take very light particles like hydrogen and helium and you cram them together at very hot temperatures. That also makes lots of energy. The problem with fusion is that you do need very hot temperatures. There are all these experiments trying to explore the physics required to heat plasmas to these extremely high levels. It's very, very hard to do. Basically, it boils down to making something that's hot but not loosing it's heat to the walls or whatever is holding it in. In this picture you can see the Joint European Torus which is in England. This is one of the most successful fusion experiments. 

You can see this glow on the bottom and the top. This is where the plasma inside is touching the wall. This is enormously hot, and when it touches the wall it loses its heat. They're trying to confine that plasma and keep it from touching the wall. Other experiments are the Madison Symmetric Torus which is here in Madison. Also the Helically Symmetric Experiment, also in Madison. Madison is quite a hot spot this type of fusion research. The other side of the coin is astro research where we're not so interested in the power aspects of this, but more the question of space plasmas, like the one I'm trying to answer. The Madison Plasma Dynamo Experiment falls into that category. Here's a picture of our experiment. 

It is a big, red ball. We painted it red because we go to Wisconsin and we wanted so support our school. It is ten feet in diameter, or three meters. We would prefer to stay in the metric. It's supported on this frame. We took two classrooms in Sterling Hall, one above the other. We knocked out the floor/ceiling that they shared. Now we have this very tall room and our experiment is sort of sitting in between where the upper and lower rooms used to be. You can see in this breakaway diagram that there are two hemispheres kind of on their side, and we've designed them so that they can open up and close again. One's on a rolling track, so we can open it up and close it to access the inside when we want to make changes, when we were constructing it. 

And it also sets the basis of the geometry of the experiment. You can see inside this cutaway view there are rings around the inside of this ball. Just as a backdrop, this ball is made of aluminum. The wall is about an inch thick, and these rings are rings of permanent magnets. I like to imagine this experiment as if you had the Earth and you turned it on its side. These rings are the same as rings of latitude. They are all parallel to each other. So since you turned this in the side, the north pole would be at one end over here and the south pole would be at the other end over here. You can see, there's a little person here for scale. All right, so before I go on any further I realized I forgot to talk about my toys here. 

You've all been staring at them for awhile so I'll quickly, or maybe not so quickly, give you a hint of what's going on here. As you might have already guessed, this is a plasma. It's called a plasma tube. You may have seen the more common form of it as a globe with a little ball in the center, then tendrils of current coming out of the ball and hitting the glass. This is very similar. What's happening is that this tube is full an inert gas. This is probably neon. I don't know for sure, but I think it's full of neon. Then you have two electrodes at the top and the bottom. They are conducting current between them and they're alternating their current at a very high rate, in I think the megahertz range. 

What this does is that if you this current alternating and it's at a very high voltage, a couple of kilovolts, compared to the wall outlets which are 120 volts. This is very, very high voltage, but a very, very low amount of current. There's enough energy to cause the gas inside here to turn into a plasma. This is very similar to the way we make plasma now in the Madison Plasma Dynamo Experiment. A couple of things you can see, the tendrils seem to rise from the bottom to the top. The simple reason for that is because their hot. Where the bright lines are, that's where the hottest part of the plasma is. And hot things rise while cool things sink. They rise above the cooler background gas. Also, the tendrils stick to the inside of the glass because there is what's called a capacitive connection between the current and the outside. 

You kind of experience this when you feel a static shock. You accumulate a lot of charge on your hand, if it's a dry day out, and you rub your hand on something soft. Then if you touch something metal you feel a shock. That's a transfer of charge from your hand to the metal. Since this is oscillating at such a high frequency, by touching it my hand has more conductance on the glass. I can attract the current to my hand. In comparisons to the plasmas I've been talking about this is very cool, very defuse plasma. But it's still really nice to look at. All right, I'll get to my other toy in a second. Let's see. 

All right, the Madison Plasma Dynamo Experiment has scientific goals. There are four good goals to keep in mind. We want to create a hot, steady state flowing unmagnetized plasma. I'll go over what each one of those means and how we accomplish that. After we do number one, we can investigate for different flows in our plasma generate magnetic fields. So first off we need to make a hot plasma. There are two ways we can do that. Way number one is we can use microwave energy, like I said before. This is basically the same as microwaves at home, except a lot more powerful. Your microwave in your kitchen is about 1.2 kilowatts if it's a standard microwave. 

We plan to put up to 100 kilowatts into our experiment. So that's like a hundred of your microwaves just kind of strapped to the side of a big ball. It works in a slightly different way than your microwave works. In your microwave, the waves that it emits are resonant with the water molecules in your food. That's why you put water on things to heat them up in a microwave. It's the water that heats up. There's no water in our experiment, but our microwaves are resonant with the plasma particles as they orbit around magnetic field lines. So magnetic field lines, if there's a charged particle that goes near one, it kind of gets trapped and starts orbiting the field line. The rate of this orbit, how many times per second, if you tune your microwave to equal that, you can dump lots of energy into your plasma. The other way we can heat our plasma is exactly the same way this is being heated, electrical discharges. 

That's the same way neon lights, for example, are heated. You have a current pass through them and what's call Ohmic heating transfers energy from the current into the plasma. This is the same thing that makes light bulbs work in a very different way. You pass current through a very small filament, and the fact that you have current going through something that is what's called resistant to current, means that you have a big transfer of energy into heat. So light bulbs are a great example of Ohmic heating. We are sticking electrodes into our plasma and passing a lot more energy than your standard light bulb, 50 amps and 400 volts per electrode is kind of what we're up to right now. If you do the math, that's 20 kilowatts, which is again, nothing to sneeze at. Here's a picture of one of the plasmas we've been able to make, and the electrode with which we made that plasma. This purple cylinder at the end is a ceramic that is very good at emitting current. What we have to do to have it admit lots of current is you have to heat it up to very high temperatures. 

We have a filament similar to a light bulb filament inside this cylinder. We heat it up to about 14,000 degrees Celsius. Then when we put that into our machine, we fill the machine with an inert gas like argon or helium. Then we draw a current between this hot electrode and another cold electrode that's stuck in the plasma at a different point. What we get are these beautiful plasmas. In this picture you can kind of see the two hot electrodes. The first one's this bright spot here. The second one is the bright spot on the other side of the machine. You can even see a ring around the machine where these electrodes are. All right, so like I said before, we have this big spherical vacuum chamber, and there are a lot of things that go into allowing us to make plasmas that are steady state. 

They can last for seconds, if not minutes. Lots of plasma experiments are very fast, they flick on and off. It's very hard to contain the plasma for longer than a second. But with our experiment we can contain it for, theoretically, as long as we want. We haven't pushed it past 20 seconds yet, but 20 seconds is a really big accomplishment in our field. Here's our chamber. It was actually cast up in Portage, Wisconsin by a company that has lots of experience in casting aluminum truck beds. They collaborated with a company that had experience casting vacuum chambers. This aluminum vacuum chamber was cast in two hemispheres. Here's another picture of it right after it was cast. 

One of our engineers, Mike Clark, is standing here for scale reference. And here it is just after being installed in the lab. You can see on the inside there are these ring grooves that I mentioned earlier, like lines of latitude. It's into these grooves that we bolted 3,000 permanent magnets to the inside of the sphere. Here's a cool picture of it right after the casting process finished. This monster looking thing is the sand mold that was used to form the outside surface of the chamber. There's another similar mold on the inside. They're just lifting this up after pouring molten aluminum through all of these pipes. There's still lots of stuff on fire, but then it cooled down, they send it to another company that machined the inside very precisely. Then they send it to us and we put it together. 

The plasma we make is kept from touching the inside walls by magnetic fields. Magnetic fields, like I said before, turn away plasma particles. There's a balance between magnetic energy and plasma energy, magnetic pressure and plasma pressure. When there are high magnetic fields plasma has a hard time getting through them. Here's that equation I showed you before. You can see that if you have a magnetic field coming out of the screen, then a particle with a velocity coming towards that, instead of coming through the magnetic field, it's turned aside. If it's negative charged, it's turned up. If it has positive charge, it's turned down. But the point is, it's bent away from the magnetic field line. So if our wall is on the right side of the picture, this plasma particle is not going to hit the wall. 

It's going to turn around and go back where it came from. This is exactly what we do. Here is a simulation of the magnetic field of all of our 3,000 permanent magnets. It's kind of a cross-section cut of our machine. Blue is weak field, like the Earth's magnetic field. Green is stronger, and red, which you really can't see that well, is the strongest. You can see the magnetic field is extremely strong at the very edge of our device and very weak in the center. Plasma is fine moving around in the center here. It doesn't care. But as soon as it comes near the magnetic field close to the wall it turns around and heads back into the center again. 

These are close-ups of the magnets in these rings. You can see individual magnets lined up, and next to it are magnets that are covered by a ceramic protective shield. The plasma that does through, some does, the very hottest parts of the plasma do seek through, then they don't damage the magnets. Here's just another picture looking from the inside at one of the, I think this is the north pole of the machine. So we have 3,000 rare-Earth magnets. On the surface of the magnets their field is 10,000 times stronger than the Earth's field. This whole configuration is called a magnetic bucket, because it started with people literally taking the bucket equivalent of a vacuum chamber, a cylinder, and putting magnets on the outside. Then trying to make plasma inside and seeing how it reacted. This large center is unmagnetized. Now we have our steady state, we have our unmagnetized region and we have our hot plasma. 

All that's left is flowing plasmas. But first, this is a cool video. We took, with a super-slow camera, two of the magnets colliding with each other. You can see they're pretty fragile magnets. They shatter. But it's really interesting because you can see some of the-- Oh, no. What happened? Sorry. I'll try that again. You can see some of the pieces that fly off. Some of them just leave the screen and never come back. 

But some of them turn around, come back, and are pulled back in these weird little orbits. That little guy kind of stops, then he gets sucked up. So these are super-strong magnets. Now we need to make our plasma flow. This is a way-- It's kind of hard to make plasma flow because we can't stick a fan or a motor into the plasma and stir it. It's really, really defuse. The pressures we're working with here are millions of times less than the atmosphere pressure we're breathing right now. So you really can't stir anything up. But there's a cool thing about plasma physics, that it you have a magnetic field and you have an electric field, and they're perpendicular, they're at right angles to each other, they will drive a flow in the third direction, in the direction perpendicular to both of them just like the cross product I talked about earlier. What we do is we used a magnetic field of the permanent magnets on the edge of the machine, then we stick in our electrodes like I talked about earlier that drive current, and we make that current go across the magnets. 

So our electric field in red and our magnetic field in blue, are at right angles. The velocity either comes out of the board or into the board depending on how you orient things. In this way we stir the plasma at the edges. Then we rely on the viscosity of the plasma to make the middle spin. You spin up the edges just like you stir up a coffee cup. If you were to take a coffee cup and spin it, the edges would start spinning with the walls first, then eventually the whole cup of coffee would be spinning in sync with the walls. So far, to this date, we've measured velocities up to ten kilometers per second at the wall. So this is a great thing about plasma, even though it's so defuse, it's so light that you can make it go so fast without putting a lot of energy in. This is a cool little video of how we're spinning it. Again, here's a picture of the machine opened up a little bit. 

This is one hemisphere, this is the other. This is the orientation of this video. It's a little hard to understand at first, but this line down the center is the equator of the machine. You have the north pole at one end, the south pole at the other, and we're taking these two hemispheres and rotating them in opposite directions. We're driving flow so that one hemisphere goes clockwise, the other one goes counter-clockwise. On the top half of this you're looking at the flow in the east-west direction along the lines of latitude. Red is in the board, blue is out of the board. One the bottom you're looking at the flow in the north-south direction. These lines show you the direction of the flow, and the color shows you how strong the flow is. As I play this you'll see that we start spinning at the beginning and then the velocity works it's way inward. 

It eventually reaches a steady state where you have this one hemisphere spinning clockwise, and this other hemisphere spinning counter-clockwise. You also have this big north-south flow that builds up as well. This is the type of flow that we're trying to-- that has been predicted to generate dynamo action in all these simulations that have been done. This is what we're trying to do in our experiment. Here's a diagram that was made for a similar experiment. We don't have propellers, but the flow is the same. Each of these lines describes the flow of a plasma particle. You can kind of see they're going in a east-west motion, but there's also north-south motion. You have these two distinct cells of fluid motion. How much time do I have left? Let's see. 

All right, so this video is just another look at what's going on. Again, we don't have propellers, but the motion is the same. This is really the definitive look at why we expect magnetic fields to get bigger in this experiment. These are two magnetic field lines. Green is pointing north, red is pointing south. When you spin up the plasma-- Oh, no, I clicked it too much. There we go. When you spin up the plasma in opposite directions you start to bend the magnetic field lines. It's kind of like they've been caught in the flowing plasma. They're kind of stuck in it so they have to move along with it. 

The flowing plasma stretches out the magnetic field lines and turns them back upon themselves. It turns out when you have a magnetic field line and you loop it back on itself, it's the same as saying it's gotten stronger. You started with one magnetic field line pointing up, and now you have two magnetic filed lines pointing up. That means you've increased your magnetic field. So you can see here this all getting tangled up, but you're looping your magnetic field back on itself. Now I can show you my second demonstration. This is a good example of how magnetic field lines are moved by moving, conduction things. We're going do the opposite. Instead of taking a stationary magnetic field and a moving, conducting fluid, we're going to take a stationary, conducting piece of metal and a moving magnet. You see that the magnet, when I drop it, is held up. 

It doesn't move as fast as it would want to. Instead of falling really fast, it slowly tumbles its way down. I can convince you if I just drop it like this, right? It falls as fast as it wants. But again, if we have this conductor next to it the magnet is slowed down. The magnetic field lines are "trapped" in the conductor. Another good example of this is using a copper pipe. I have a copper pipe and a steel ball. This is not magnetic, it's just a steel ball. You drop it through, it falls as fast as you'd expect it to. But if we take a very similarly-sized ball that is a magnet and we drop it. 

I don't even have to switch hands. I can drop it on top, and catch it on the bottom. So again, the magnetic field lines coming out of this magnet are slowed be the presence of this conductor. Again, I'll drop it, and it falls much more slowly. A similar thing is happening in our experiment, but instead of having a moving magnet and a stationary conducting material, we have our magnetic fields that start out stationary, and the conducting material grabs it and twists it up as it flows in the way I showed you. So where are we now? Well, we're a really young experiment. We made our first plasma last September. I was really excited. The chamber itself was installed in January of 2012. So we spent the first three-quarters of 2012 assembling it, putting in all the required heating, making the hot electrodes I showed you as well as installing all our vacuum pumps. 

The last piece of the equation is inserting things to measure the flow, the temperature, the density of the plasma. We do that with probes that we stick into the plasma. We use, in plasma physics, the principles of electricity magnetism at the tip of the probe to determine what the temperature, what the density and the flow is in the plasma. Right now we have four of the hot electrodes that I showed you installed on MPDX. And we're building four more electrodes so that we can recreate that simulation I showed you before. This is the same picture. I rotated it back so that it's kind of in the same orientation as the Earth with the north pole at the top and the south pole at the bottom and the equator at the center. But the point is, the top hemisphere is spinning one way, and the bottom hemisphere is spinning the other way. You can see, we're sticking in these electrodes at the very edge and spinning the plasma at the very edge. The velocity is the highest right next to these electrodes, but it doesn't disappear right away. 

It works its way inward. Because the plasma has viscosity just like molasses has viscosity, or water has viscosity. It's just on a very different scale. This is what we're shooting for. When we have all these electrodes in place we'll be able to recreate the flows that we would predict will generate magnetic fields. But we've already made lots of cool and interesting plasmas. Here are some pictures that I'd like to show you. These are both pictures of argon plasmas. Here you can really see the magnetic field structure at the edge of the machine. This was taken kind of looking very obliquely through one of our windows on the side. 

You can see this little needle point right here. That's all of the plasma that's allowed to touch the magnet. Here's a diagram of the magnetic field structure at the edge. I don't know if you guys can see that there. Those lines are kind of faint. But basically you have these curved lines connecting north and south poles of these magnets. This little cusp is the plasma that sneaks down, this blue arrow, for example. But everywhere else on the wall the plasma is turned away. Basically, we're taking this gigantic sphere, the inside of this sphere, and instead of the plasma being lost in the entire inside, it's only lost along these tiny, thin filaments. That means we can hold our plasma inside and keep it hot for much longer. 

We also have seen these really cool ring formations when we pull our electrodes back into this magnetized region. The plasma is stuck between the magnets, in between these magnet rings. They make these really neat looking shapes that go all the way around the machine. Here's another picture of one. You can see the hot electrode right here, and the plasma beam goes this way in this clockwise direction. It actually makes it all the way around the machine and this is the tail end of it right here. You can see plasma fills the rest of the chamber as well. This is something we're very excited to see because this is basically a visualization of the plasma flow. The flow is in this clockwise direction. That's what we set it up to be and that's what we've measured it to be. 

And this flow, even though you can only see it in this edge region, we think, permeates throughout this entire hemisphere on that side. As we add more hot electrodes we'll just make it spin faster and more evenly, and get closer to the flows we want to excite. In summery, the Madison Plasma Dynamo Experiment. We ended with a X because it's much cooler than ending it with an E, so we can say MPDX instead of MPDE. Much cooler. We're just beginning to yield valuable results. We're a very young experiment, but we're moving very quickly. Practically every week we're finding ways to dump more power into our plasma to make it hotter and denser and spin faster. The velocities we're measuring are getting close to what we predict will start generating dynamo action. Now we haven't started looking for magnetic field growth yet, but when we do we hope to observe magnetic fields growing inside of our machine. 

Yeah, so as I finish I'd just like to acknowledge all my collaborators in this work. The head of this project is Dr. Cary Forest. He's the primary investigator. It was basically his brain-child. This entire experiment is thanks to him. We have an engineering team of two very capable engineers, John Wallace and Mike Clark. A couple of post docs, Chris Cooper and Ivan Khalzov. Ivan is extremely crucial in simulations. He was responsible for some of the simulations I showed you today. And Chris Cooper has a lot of experimental experience. 

Our core of graduate students are Matt, Cami, Ken, Yan, Jason and myself. We also have a very willing and capable group of under-grads who we usher into the plasma physics world and get them started, and hopefully get them started on their way to graduate school and beyond. So that's it. Thank you very much. [applause]