Sunny Starscout explains why the Large Hadron Collider is so large · 2:54pm Jul 3rd, 2021
Sunny Starscout rolled down a slope, with wheels on all four of her hooves. The conversion of gravitational potential energy to kinetic energy caused her to accelerate towards her four friends. She leant to one side to bend her trajectory to circle around them.
“The Large Hadron Collider,” she said, “or LHC, is the world’s largest particle accelerator. It accelerates beams of protons to very high energy. They then smash together, and by studying these collisions we can learn more about the structure of matter and the fundamental forces and particles that make up our universe. It’s built in a 27-kilometre circular tunnel.”
“Why does it have to be so big if it’s studying something so small?” asked Pipp Petals.
“If you want to move something in a circle,” said Sunny, kicking her hooves to maintain momentum while continuing to circle her friends, “you need a centripetal force to bend its path inwards, or it will just keep going in a straight line. The centripetal force is equal to the mass times the speed squared, divided by the radius of the circle. It’s easy to move slowly in a circle.” She circled the group of ponies again at a leisurely speed, while smiling to show just how easy it was. “But if you move too fast and turn too quickly, that needs a bigger force and you can skid.” To illustrate this she looped around and kicked hard to accelerate to a high speed, then twisted her hooves so quickly that she skidded, leaving a pink line on the ground as the wheels of her skates scraped the paving stone. Losing her balance, she crashed into Hitch Trailbrazer, who in turn fell against Pipp and everpony toppled to the ground.
“Oops,” said Sunny, getting up on her wheeled hooves. “Anyway—the protons in the LHC have an energy of seven tera electron volts. They are moving at close to the speed of light. The beams are bent into a circle by superconducting magnets. Because they are moving so fast, they can only be bent in a circle with a very big radius. This means the Large Hadron Collider has to have a circumference of 27 kilometres.”
“I thought it had something to do with synchrotron radiation,” said Zipp Storm, flapping her wings to shake out the dust and brushing a comb through her messed-up mane. “You bend a beam of charged particles in a circle and it radiates x-rays and loses energy.”
“That too,” said Sunny. “Synchrotron radiation stops us accelerating electrons to a very high energy in a circle. But protons are heavier and don’t lose nearly so much energy that way. For protons, the limiting factor is the bending power of the magnets. Even with superconductors, we can’t make a magnetic field big enough to turn them in a smaller circle.”
Thanks to Super Trampoline for posting the gif that inspired me to do this. This is adapted from a video I did with some students for a local science festival, where we explained particle accelerators at a playground. When I wrote the draft script, I wanted a brief scene with someone doing stunts on roller blades. Unfortunately, I don’t have that kind of agility, I couldn’t find any suitable extras, and I didn’t have time to write a risk assessment. So, I settled for a much less-cool clip of me riding a bike.
Rollerblading down a fieldstone road? That's gotta' be hard on the knees.
Also, I think rollerblade pony being an LHC expert needs to be fanon-to-canon just like Derpy. I so want Sunny boring/confusing her friends with beam dynamics and magnet parameters and things!
Earth ponies doing wheel spin power slides during the supermarket trolly dash.
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Headcanon accepted.
Sunny is a Nuclear Physicist. I can dig that.
Observation: Sunny Starscout on roller blades is just freaking adorable, and I need more. Her explaining particle physics and the LHC is perfect. Clearly she's hyper-body-aware, so making analogies to travelling protons is also perfect. And cute.
So I have questions! If you're willing.
Looking at that cutout, it just occurred to me, and I'm asking out of complete ignorance: How symmetrical is the magnetic field structure around the proton flight path, or tube? Being in a circle, wouldn't the magnetic field lines bunch up just a little on the inside diameter of the tube as opposed to the outside? Does the applied centripetal force require a stronger field on that inside diameter?
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Good Question! I think there would be slight asymmetry, but would it matter? The important bit of the fields is the "outside" that repels/deflects the protons, innit? I think you might use less power if you could make the fields symmetrical, but that's got to be a relatively tiny effect. (Speculation by an amateur enthusiast, of course.)
(Sunny is absolutely adorable, BTW!)
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Good point! If it matters, then maybe the outside might actually need more strength, which would make the engineering more complex (I think, maybe, but I don't know). I need answers, heh!
Also, I absolutely love how amazingly "accurate" Sunny's little loop looks, especially at the end where she places her 'toe' down as though she's applying a skate brake (or just being cute). Her stance looks entirely natural, to the point where I have to remind myself that she's got four legs to control and balance, not two. Someone spent a lot of time and effort making that look as subtly amazing as it does.
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Can't mo-cap a skating pony!
Oh yeah, the character animators on the movie are absolutely stellar!
Wait, I just noticed: do all the G5 ponies only have a cutie mark on one side? ...huh.
I don't know where that first clip is from but it's legitimately the most and best bit of animation I've seen from g5 so far. So in addition to teaching quantum physics you're also doing a better job advertising pony than hasbro has been lately.
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I too spent a bunch of time just admiring the natural-ness and movement detail of Sunny's little rollerblade loop. Not Sunny herself - not really - but the rollerblade loop.
Leant, not lent, unless Sunny is giving them twenty bits until Tuesday for hayburgers today.
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Good question, but the answer isn't straightforward. The magnetic field structure inside a big accelerator like this is complicated. The ring isn't a perfect circle. The bending is done by 1232 dipole magnets, each 15m long. I'm not sure if they are curved, or straight but the beampipe is wide enough to accommodate the curved beam. The magnets contain two beam pipes, for the clockwise and anticlockwise beams, with the field pointing up in one and down in the other. It's design to give a fairly uniform field strength across the pipe, but it won't be perfect. And as the protons will have a small spread of momenta, they are all on slightly difference trajectories and the beam can diverge. Therefore you need a lot more magnets - quadrupoles and more - and feedback systems to focus the beam. The slight difference between the inner and outer diameter is probably one of the easier things for the design engineers to deal with.
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Nuclear physics is for the past generation. Sunny is going way deeper, studying quarks, leptons, and the structure of the proton and other hadrons.
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Neat, thanks! But (of course) that raises more questions. The first to spring to mind is the nature of the feedback systems used to help focus the beams. The pipes have to be very highly evacuated because the protons running into "stuff" would be bad... but how is the divergence detected if the protons don't run into... uhm... stuff?
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I'm not an accelerator guy - my job is detectors - so I'm not too sure of the details, but I think they measure the electric field of the beam. You have a pick-up at one point in the ring that measures the profile of a proton bunch, and it sends a signal to a kicker magnet on the other side of the ring.
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Cool, thanks!
5548312 Thanks for the answers! I have so many questions, but that's a deep rabbit hole.
I was thinking that the LHC is about as complex as it is huge, and I can't imagine that any one person would be able to keep all of the details of its construction and operation in their head. It really is an astounding piece of technology.
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I sometimes miss the days when I was working a project sufficiently small that I felt I could understand everything. Now I can't even keep track of all the components in the Inner Tracker Detector, which is just one part of the ATLAS detector - it has a design report over 500 pages long.
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Thanks. Fixed.
In the Book "The Gods Themselves" by Isaac Asimov, the collider on the Moon is hundreds of kilometers across.
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Imalou, the designer, also made Sunny and Izzy cute.
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Yep! No B-team on this movie, it seems.
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You wanna go real sci-fi crazy? Imagine if you flipped the loop sideways and just had it follow the entire circumference of the Moon. (This'd also even out the effects of gravity, which I suspect would matter with a sufficiently large loop)
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In "Global Collider Generation: An Idyll" by Paul Cornell, a muon collider is built encircling the Earth. My guess is future generations of scientists will see this as a sort of steam punk.
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To Quote the Borg:
When we shall become a K2-Civilization, we can build a collider with a radius of 1 parsec, a diameter of 2 parsecs, and a circumference of TauParsecs. We can power it with 10^26 Watts from the Sun (that is only a quarter of the the Solar Output, thus leaving the rest of the power for other projects).
Replace the cavemen in this comic with rock farmers and there's an argument for earth ponies being the first to research into particle colliders:
media.discordapp.net/attachments/814876932604035123/993876144153694329/unknown-9.jpg