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When you collide protons at an energy that's far below its mass, the proton acts as a single object. This is the regime in which nuclear physics typically occurs; all of the reactions that break nuclei apart, and the energy that holds them together, are typically small enough that it works to treat the proton as a single unit most of the time. This includes nuclear fusion; the mass of the proton is 938 MeV, and the amount of energy required for nuclear fusion (15 keV, as we said) is about a million times smaller than that.

When you collide protons at an energy that's far below its mass, the proton acts as a single object. This is the regime in which nuclear physics typically occurs; all of the reactions that break nuclei apart, and the energy that holds them together, are typically small enough that it works to treat the proton as a single unit most of the time. This includes nuclear fusion; the mass of the proton is 938 MeV, and the amount of energy required for nuclear fusion (15 keV, as we said) is tens of thousands of times smaller than that.

If we instead decide to collide protons at energies that are higher than a few times the proton mass, then there is now enough energy in the reaction for the quarks inside the protons to interact with each other directly. We can no longer treat protons as single objects, since the energy involved in the reaction is enough to expose its inner components. As the collision energy becomes higher and higher, the binding energy of the proton becomes less and less relevant, and the picture of two dense clouds of quarks and gluons interacting becomes more and more accurate. These reactions have enough energy to produce all manner of exotic matter, particles that you could never find in a nucleus, nor could you create them by nuclear fusion. The current energy of the LHC is roughly ten million times greater than the mass of the proton; at those energies, the proton's mass and binding energy are completely negligible, and the interesting reactions are entirely driven by individual quarks and gluons interacting with each other. The proton is merely a vehicle for us to deliver bits of fundamental matter to the collision site. If there were a way to just collide free quarks and free gluons, without all the mess generated by the proton, many particle physicists would jump at the chance. (Unfortunately, this turns out to be impossible.)

If we instead decide to collide protons at energies that are higher than a few times the proton mass, then there is now enough energy in the reaction for the quarks inside the protons to interact with each other directly. We can no longer treat protons as single objects, since the energy involved in the reaction is enough to expose its inner components. As the collision energy becomes higher and higher, the binding energy of the proton becomes less and less relevant, and the picture of two dense clouds of quarks and gluons interacting becomes more and more accurate. These reactions have enough energy to produce all manner of exotic matter, particles that you could never find in a nucleus, nor could you create them by nuclear fusion. The current energy of the LHC is roughly ten thousand times greater than the mass of the proton; at those energies, the proton's mass and binding energy are completely negligible, and the interesting reactions are entirely driven by individual quarks and gluons interacting with each other. The proton is merely a vehicle for us to deliver bits of fundamental matter to the collision site. If there were a way to just collide free quarks and free gluons, without all the mess generated by the proton, many particle physicists would jump at the chance. (Unfortunately, this turns out to be impossible.)

So, given this, why aren't LHC physicists worried about triggering nuclear fusion? The answer is fairly straightforward: though each individual proton has an energy a billion times larger than the fusion threshold, the total amount of energy that is released into the surrounding area is still rather manageable, on a macroscopic scale. After all, 13 TeV is still only about a microjoule of energy, which is around a billion times less than the amount of energy that the Sun imparts to a square meter of Earth every second. That said, there are around 600 million collisions per second happening, so you definitely don't want to be standing anywhere near the interaction point, and the detector electronics have to be specially designed to deal with the extreme high-radiation environment. But we're talking about around a few kilowatts, at most, of radiation released into the environment at each collision site. That's a pretty human-sized amount of power, and is roughly equivalent to the heating power of a large space heater. This was by design - the collision rate at the LHC was chosen partly so that it would be feasible to build a detector that could withstand the influx of radiation. Nuclear explosions require many, many reactions all occurring at once, which is why they have such destructive power. The LHC collides at most a few individual protons at a time.

So, given this, why aren't LHC physicists worried about triggering nuclear fusion? The answer is fairly straightforward: though each individual proton has an energy a billion times larger than the fusion threshold, the total amount of energy that is released into the surrounding area is still rather manageable, on a macroscopic scale. After all, 13 TeV is still only about a microjoule of energy, which is around a billion times less than the amount of energy that the Sun imparts to a square meter of Earth every second. That said, there are around 600 million collisions per second happening, so you definitely don't want to be standing anywhere near the interaction point. This is especially true since the individual particles of radiation released are much higher in average energy, meaning they're much nastier in terms of damage to life and inanimate objects than the radiation from the Sun. Because of this, the detector electronics have to be specially designed to deal with this extreme high-radiation environment; human access to the experimental hardware is also very tightly controlled, and is completely forbidden when the accelerator is running. But ultimately we're talking about around a few kilowatts, at most, of radiation released into the environment at each collision site. That's a pretty human-sized amount of power, and is roughly equivalent to the heating power of a large space heater (but, again, in a much more damaging form than the heat released by a space heater). This was by design - the collision rate at the LHC was chosen partly so that it would be feasible to build a detector that could withstand the influx of radiation. Nuclear explosions require many, many reactions all occurring at once, which is why they have such destructive power. The LHC collides at most a few individual protons at a time.