system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do particle accelerators have to be so long? Why can't the same speeds be achieved with a smaller circle?
gpt
Think of it like a NASCAR race.  If they were to hold it in a very small parking lot, they would be constantly turning, and have to go very slow.

You can then move it to a very large parking lot, and now you can go faster.

If you can build a race track, you can go even faster.

The reason you can go faster is because turning takes away energy.  You simply can not go as fast when you are using up energy to constantly turn.  You could build a straight track, and get higher speeds, and that idea has been proposed.  The downside is you send to particles at each other, and they pass each other once.  In a circular track they pass each other thousands of times a second, so you get more collisions.