system
Given the following post, respond as if you're commenting on Reddit:
human
Why is the large hadron collider so... large?

The LHC is huge (17 miles in circumference, actually).. What is it about the process that makes this necessary?
gpt
Magnetic fields are used to bend the path of the protons. The protons are going so fast that even with the most powerful magnetic fields we are able to produce, we can only bend their path so much. This is what dictates the size of the circular accelerator. If we were to make a proton accelerator with higher energy than the LHC, we would either need to make it larger, or invent more powerful magnets.

EDIT: As anyanyany points out, there is a separate issue that is due to the fact that charged particles radiate away their energy too quickly if they are accelerated in too tight a circle. This is less an issue with protons (the particles in the LHC), because they are heavy, and so radiate less (the radiation is proportional to the particle's velocity, and for a given energy electrons must go much faster than protons). For protons, the biggest problem is actually bending their path with magnets. For electrons, the biggest problem is the radiation loss.