They don't really provide details, but generally yes. If you have achieved your desired energy, you might then want to irradiate something in air (remember some of this was used in weapons research). So he could have stuck his head in front of the beam exit, or they might have pulled apart a section of the accelerator, sealed it off, but for some reason the beam was still run and the beam simply passed through the seal.
I'm guessing that he was probably working on one of the beam dumps (not the main accelerating ring), which meant that the beam could have already been accelerated many times around the synchrotron.
I'm guessing that he was probably working on one of the beam dumps (not the main accelerating ring), which meant that the beam could have already been accelerated many times around the synchrotron.