By selecting the energy of the proton beam correctly, you can prevent much besides the muons from being produced. Whatever other particles do show up - if not g

By selecting the energy of the proton beam correctly, you can prevent much besides the muons from being produced. Whatever other particles do show up - if not guided by carefully set up electromagnetic fields - will quickly smash into the walls of the device, generating heat as they scatter and decay. Some of this heat can be used to boil a coolant and regenerate energy, but for the most part it is just an inefficiency. The lead wall and some of the material around it will become radioactive waste as some long lived isotopes are produced, but they could potentially have many years of service life.