Accelerator Science: Circular vs. Linear
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Accelerator Science: Circular vs. Linear


If you’re a fan of my videos, you know that
I’ve been on an accelerator kick for the last few. And if you’re not a fan, then why the heck
not? You should take a look, ‘cause, well- accelerators
are very cool. Now there are lots of different shapes of
particle accelerators, but when we’re talking about cutting edge research, there are two
main ones: one of them is circular and one of them is a straight line. So I thought I’d tell you about the pros
and cons of the two different choices. But first, to understand the differences,
you need to know how particle accelerators work. The principle is actually really simple. You use an electric field to push a particle
with electrical charge and that particle goes faster. Now the concepts of electric charge and electric
fields aren’t the most common ideas, so let me use a more familiar situation to help
me make my point. Now you all know about gravity and how it
works. There is a gravity field that points downward. That gravity fields interacts with objects
that have mass and those objects get pushed downwards. That, by the way, is a techno-geek way to
say that things fall when you drop them. But now imagine if you were to change the
direction of gravity. We’re going to cheat a little bit and pretend
that there is a cartoon kind of gravity that is a little different than ordinary gravity. I’m going to hold this cartoon ball and
see what happens if we have cartoon gravity point to my left. Maestro- can you point cartoon gravity to
the left and give me a cartoon ball? Super. Now, if I let the ball go, what happens probably
won’t surprise you. The ball falls to the left. If cartoon gravity points in some other direction,
then the ball will fall in that direction. Here, let me show you. Maestro, can you pick a direction? Now, I’m going to cover my eyes. Don’t tell me what it is- surprise me. Now materialize a ball in my hand. When I let it go, let’s see what it does. So it went that way. So that means that cartoon gravity was pointing
that way. Now, cartoon gravity isn’t a real thing. We can’t arbitrarily point gravity in any
old direction. However we can do that with electric fields. Let me show you how. The easiest way to make a simple electric
field is to get two metal plates like these here. If we connect the two plates to the opposite
sides of a battery, it will set up an electric field between the plates. We won’t make that connection just yet. Now we also need an electrically charged object. Okay, so now we’ll connect the wires from
the opposite sides of the battery to the plates and let’s see what happens. So we connect the one wire. Now focus on the ball. I’ll do a countdown on what happens as we
connect the other wire: 5, 4, 3, 2, 1, connect. Voila! The electric field makes the electric charge
combine to make a force. Okay, so that’s the electric field and charge. What about the circle vs. line thing? Suppose we wanted to use the very strongest
electric fields possible and wanted to make a beam of particles with the energy of the
Large Hadron Collider, or LHC, which is the highest energy particle accelerator in the
world. What would a straight accelerator look like? Well, a strong, but technically feasible electric
field might be about 25 million volts per meter. Since the LHC has a design energy of 7 trillion
electron volts, that would take an accelerator about 280 kilometers or about 170 miles. That’s about from New York City to Providence,
Rhode Island. So, building an accelerator that long would
be hugely expensive. So that’s where circular accelerators come
in. Circular accelerators have some elements common
to straight ones and some new features. To begin with, a circular accelerator doesn’t
have accelerators all around the circle. Instead, what they have is a relatively short
length of accelerator and the rest of the circle are a series of magnets. When a charged particle moves through a magnetic
field, it moves through a circular path. In the case of the LHC, the whole accelerator
is 27 kilometers around, or a smidge over 16 miles, but the portion of the circle that
is an accelerator like we’ve talked about so far is just over two meters or six and
a half feet. Over those few meters, the electric field
is effectively 8 million volts per meter, although if you look it up, you’ll find
different numbers for technical reasons. The outcome of this design means that when
a proton, which is the particle accelerated by the LHC, goes through the acceleration
region, its energy goes up by 16 million electron volts. With each orbit, the beam gets more and more
energy, cycle after cycle. It’s like a child’s merry go round, in
which an adult throws the same handle over and over again as it spins. The merry go round goes faster and faster. Of course, at the energies involved, the beam
is already moving near the speed of light, so the beam doesn’t actually speed up. But it does gain energy and the basic analogy
is sound. So let’s think this through. To get the 7 trillion electron volt design
energy of the LHC, the beam would have to go around the circle about 410,000 times. Given that the LHC beam moves at basically
the speed of light, it goes around the circle about eleven thousand times a second. So that means the LHC could, at least in principle,
accelerate a beam to design energy in 36 seconds. Now it actually takes longer than that, but
that’s because as the energy of the beam increases, the strength of the magnets also
have to increase to make the beam travel in a circle of constant radius. On the other hand, a circular accelerator
is harder. In the case of the LHC, the beam goes around
eleven thousand times a second and the beam can circulate in the machine for twelvish
hours. That means everything has to work to incredible
precision to keep the beam inside the accelerator. So that’s one minus for a circular accelerator. There’s another consideration about linear
vs. circular accelerators. When you force an electrically charged particle
to move in a circle, it gives off radiation, which makes it lose energy. This radiation is not the same for all kinds
of particles. Very massive ones such as protons lose energy
much more slowly than light ones, such as the electron. Thus it is much harder to make a high energy
circular electron accelerator than a proton one. To hang some numbers on that statement, the
tunnel that holds the LHC proton accelerator used to hold the LEP electron accelerator. The LHC can accelerate protons to over 150
times the energy that the LEP accelerator accelerated electrons. This radiation that electrons emit when moving
in a circle is why scientists are thinking about a linear accelerator for the next big
electron collider. This is called the International Linear Collider
or ILC and it’s in the design stages. There is no guarantee that it will ever be
built. So these are the big differences between a
linear accelerator and a circular one. A linear one is simpler, but it takes a very
long one to reach very high energies. A circular accelerator reuses a short linear
accelerator over and over again, but it requires a lot of precision. And linear accelerators are potentially better
if you want to accelerate high energy electrons. Which you choose to build depends on your
research needs and both techniques can be used to help scientists to better understand the world around us.

53 thoughts on “Accelerator Science: Circular vs. Linear

  1. Does it have to be underground to shield humans from radiation, or the experiment from outside radiation, or is it merely so not to be an obstacle in our environment? E.g. could it be build at ground level somewhere in the desert where nobody cares?

  2. In the wake of the election that troubles me deeply, thank you Dr. Lincoln for soothing me with the subject of physics (which I major in, condense matter, but I'm also a huge fan of particle physics).

  3. Very cool and informative, thank you. Ever thought of doing some basic field experiments as examples? I always loved the magnet bottle lol

  4. Could you do a video on why charged particles radiate energy when they are pulled at an angle? (That's still called bremsstrahlung right?)

  5. This may be impractical but what if you accelerate the particle then launch it at something. Would it be powerful? This might work as an asteroid defense. Yeah it sounds like sci-fi but i curious

  6. In circular orbit at close to "c"…does the centripetal acceleration and resultant force which is being opposed by magnets to keep them in circular effect behavior of particles and or their properties compared to linear accelerators? Must be a huge outward force. Cherenkov radiation ? שלום

  7. 1:06 ive learned that objects follow straight lines in a curved spacetime so they arent neighter pushed nor pulled, arent they?

  8. If an electron is traveling as the lone-1s¹ companion of a nuclear ion {He, Fe, Au, U,…}:
    —does that electron itself emit synchrotron radiation around the circular accelerator…
    —is the electron's emitted synchrotron radiation stronger by its combined velocity…
    —do both the nucleus and, the electron, emit synchrotron radiation…

  9. In a way you can tell gravity (of an accelerated object) where to go. Accelerate something at the "speed of light" and it's acceleration (energy) would equate to is mass, any momentum passed that point (say in a black hole) would be more mass for acceleration. So if an object goes that fast the space it's in will move in the opposite direction(external force moving in), It's why things appear quantum.(Ex.neutrino) Light doesn't bend around objects the space just bends along with any light in it. If a fill a ballon (particle with energy in space) with water it will float in water fill it with cement (more/dense energy) it will sink.

  10. Thanks for the video. Question. It is mentioned that it would actually take longer than 36 second to accelerate to design energy (at 5:36). And that this is because of the ever higher energy. Is this because the proton is increasing in mass therefore not accelerating (increasing velocity) as much per push? Please clarify thanks…

  11. My favorite part of the channel is the complete 90's kids show vibe I get from every video. It reminds me of reading rainbow or mr rogers (in some ways).

  12. Scientists are eating the science up, the money makers are waiting for the next power source breakthrough.

  13. Hi prof. I need an answer how do electrons revolve around nucleus.. so., that i should not have any doubts in future

  14. let's just get to the crux of the matter; 11,000 rps = 666,666.6 rpm. You're a pseudo science maniac and someone has to stop this before it creates a loop in time and we all get caught in a time loop in which we are all going around in a time loop created by a time loop in which we are all going around in a time loop created by a time loop in which we are all going around in a time loop created by a time loop in which we are all going around in a time loop created by a time loop in time.

  15. thank god you have no idea what you're doing but seriously stop. just stop. You got this design from matchbox car tracks. You're a kid with a book of pictures of matches.

  16. What ever happened to the word Excelerate or was it Excellerate ? Don't tell me that wasn't a real word. Accelerate means circular motion. Excelerate or Excellerate means linear motion.

  17. Hi.
    Just for fun, I was wondering if you could maybe give us an explanation of what type of components would be needed to create a Ghostbusters proton pack.
    Not necessarily considering weight and size, but just what would be needed in terms of individual components, power requirement, and such…and what a real one might look like if a realistic proton pack was constructed with today's knowledge and technology.
    What would the Ghostbusters need to do, to create an actual proton pack??

  18. How would a physicist know what particles are created, minus the umbrella explanation of "computers". I want to make an atom smasher, can anyone share a link or two?

  19. So I have this idea for an accelerator that works like a small version of the LHC, But when time to collide, an electron and neutron are also injected to the collision site. Basically building an atom via high-speed smashin. Rather than the other method of shooting down a massive particle to the correct state, like how fission reactors work.

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