How is a cyclotron constructed and how does it work?

The cyclotron is a charged particle accelerator. It worked well enough to net Ernie Lawrence, its inventor, a Nobel Prize in physics for creating and developing it. (Props to Hungarian SÃ¡ndor GaÃ¡l, but word on the street is that he was a bit later than our boy Ernie.) This thing isn't all the complex, but since we're here on the page, we'll have to jump around a little bit to get it all laid out.

Better buckle up. We'll touch on theory here and there and do the mechanics along the way in bits and pieces to arrive at a working end product. Hopefully.

Let's build one, plug it in and fire it up to see what happens. Use the links where suggested. (You won't be Rickrolled.

Promise.) We'll start with a bit of background. Ready? Step up.

One of the four basic forces in the universe is the electromagnetic force. Not the electric force. Not the magnetic force.

The electromagnetic force. Electrostatics and magnetics are inseparably intertwined. Any time a charged particle moves, it creates a little magnetic field around its path of travel.

All the time. Every time. That sets the stage for interaction between charged particles and magnetic fields.

Any time there is relative motion between a charged particle and a magnetic field, a force will act between them. Movement can result. Relative motion means the charged particle must be moving "across" or "through" magnetic lines of force and not "along" or parallel with them.

You already know the basic law of electrostatics: opposite charges attract and like charges repel, yes? Good. Let's jump.

Picture a hockey puck. Now picture it bigger in diameter, but not in thickness. Make it as big as, say, a small dinner plate.

Got it? A thin disc is what we've got. Now picture it made of metal.

Now picture it hollow so we have only the shell. Just a dinner plate sized disc that's hollow. We good?

Now cut it in half across its diameter and you'll have two things shaped like the letter "D" and they'll be hollow. Put them in a fixture to hold them in the position they were just after you cut them. What you've got is your original disc cut in half with the openings facing each other and a little gap between them.

That hollow space inside is the "cavity" and it's going to be the "playground" for our particles. And the gap between them is going to let us hook up a power supply to the two halves, to the two D's, and charge them oppositely when we need to. A couple more things and we're tight.

First, punch a hole in the outside of a D to form an exit from the cavity. Then put the whole thing in a close-fitting package so we can pump all the air out from inside and around the D's and their little electrical insulators that support them. Remember the little hole we made in one of the D's?

We need to have a hole in our package to let the particles out after they come out the hole in the D. Now focus. The particles are going to be coming out in a tangent from the edge of the disc.

Picture this clearly. A particle is going to be moving along the inside edge of the cavity in a virtual circle. It's going to be moving in a circular path, and will slip out the exit and travel in a straight (tangent) line coming out from there, and that's the way we have to arrange our "exit tunnel" from the setup.

If someone was swinging a weight on a string about himself, and the string broke, the weight would fly off in a straight line, a tangent, from the point where it was when the string broke. Our hole in the D and the outlet tunnel or tube will facilitate that kind of exit, will make up that path, okay? Check the GSU hyperphysics link at this point to see a drawing of the internal setup and then come back 'cause we're ready to jump.

Here we go. We're gonna build a big, big electromagnet. Picture a big log.

Make it about, what the heck, three feet in diameter. It's big. And pretty long.

Now picture it made of iron. One big, cylindrical chunk of iron. Then wrap about a zillion turns of heavy gauge wire around the middle.

Leave room at the ends of the log so we can bend them. Now stand the log on end and bend both ends over and toward each other to make a big letter "C" out of them. Got it?

Our coil is in the middle of the "back" of the C and the ends come over, come around and come in to create a little gap between them. Just big enough to put our little package in. Our package is the set of D's.

It just fits inside the gap at the ends of the big C we just made. If we then take the ends of the wire we used to wrap the coil and hook them to a giant DC source, we will get a ton of current through the coil and create a super electromagnet with a crazy dense field across the little gap where our sealed and evacuated package is going to be sitting. The lines of force of the magnetic field are straight across the gap of the C, and they are perpendicular to the plane of our D's in our package.

That's an important concept. The plane of the D's is at a right angle to the lines of force of the standing magnetic field were are generating when we turn on the electromagnet. Go to the Wikipedia cyclotron article at this point and scroll down to the picture of the young woman standing outside next to a cyclotron electromagnet and pole piece assembly.

You can see this one is actually two "C's" (they're the dark things at the near and far end) that support the white circular structures. The little space between the white thingies is where our package with the D's will go. It's gonna sit right between the pole pieces.

We good? Let's review. We've got a couple of hollow D's sitting on insulators with a tiny gap between them.

We've got a wire hooked to each D so we can electrify them. We've got all that inside a case so we can pump down the pressure and create a vacuum. The package is sitting inside a sick magnetic field that we are maintaining by using enough electricity (though we use DC) to power up a small town.

Let's hook up our "D wires" to a large, high frequency alternating voltage source so we can fire the thing up and get down. Though the cyclotron can be used to accelerate electrons or protons, protons were arguably more useful to physics. And they're a lot more fun!

We just built a particle accelerator! You wanna shoot ping pong balls out of it or bowling balls, hmm? Thought so.

We need some protons. Has UPS come yet? Forget it.

We'll just make some. Where's the hydrogen? Get that gas over here.

We pump some hydrogen into a "stripper" that uses high voltage to ionize the gas. With the electron torn away, we have a hydrogen nucleus. A proton.

Sometimes with a neutron. Or even two. We get these into the middle of the cavity created by our hollow D's.

Now the fun begins! We apply a high voltage to the D's. One D is positive and the other D is negative.

The protons are positive. They are electrostatically attracted to the negative D and repelled by the positive D and they move. Oh, but bad news.

There is a wicked magnetic field that they have to swim through. So they are deflected. It's gets tricky here, but you've come this far.

It's only one more jump. As the protons are pushed by one D and pulled by the other, they move and cross the gap. And as they cross the gap, we reverse the polarity of the voltage to the D's.

The protons are, like, "We just came from over there because we were pushed out by the positive and pulled here by the negative and now you go and reverse the polarity of the voltage on the D's and we have to go back! What's up with that?" So the protons are going to want to respond to the changing voltage and go back and forth across the gap between the D's.

But with the giant magnetic field through which those little guys have to move, they travel in an arc. What happens is that as they move back and forth and gain energy and move in an arc, they actually spiral from inside to outside of the D's. Break here to focus on this: This complex motion, the vectors carved out by the moving charges in response to the electrostatic fields and to the "skew" created when their own motion-generated magnetic field interacts with the standing magnetic field we created with our magnet, is the heart and soul of what makes this machine work, is what this machine is all about.

In finishing, the positive ions (protons, plus, maybe a neutron or even two) gain energy with every moment and end up really hauling butt by the time they reach the outer edge of the playground. They fly out through the outlet (on that tangent we talked about) and down the goodbye tunnel we set up in our package and end up slamming into a target we place at the end of the run. Blamm!

Proton-target interaction. Scattering. And if we "rig" our hydrogen to improve heavy hydrogen concentration a la heavy water, we can shoot bigger bullets on a regular basis.

The capture of heavy hydrogen will allow us to up the percentage of proton-neutron nuclei and proton-neutron-neutron nuclei we use as the bullets in our particle cannon. It just seems to keep getting better! Imagine the possibilities for scattering.

Skim the articles and tighten your grip on the operation of the machine that changed physics. We've skipped some little things, and (probably more importantly) all the tedious math associated with the operation of the machine. By just sticking to basics and sketching it, we've got a fairly good idea of how the thing works.

By the way, the math isn't really tedious. And it isn't that tough. As your math skillz improve, you can come back and tear up the formulae presented in all the articles.

It isn't that difficult, really. It's not rocket science. Just nuclear physics.

Big difference. I'm doing nuclear physics!

The cyclotron is a charged particle accelerator. It worked well enough to net Ernie Lawrence, its inventor, a Nobel Prize in physics for creating and developing it. (Props to Hungarian Sándor Gaál, but word on the street is that he was a bit later than our boy Ernie.) This thing isn't all the complex, but since we're here on the page, we'll have to jump around a little bit to get it all laid out.