Sligh correction: here, they are colliding with enough force to skip straight to the OXYG and PLUT stage. Other elements could be produced at lower energy (most often you see this as clouds of NBLE produced when a proton beam hits INSL)
Protons are hydrogen nuclei and so TPT allows them to fuse like elemental HYGN. Here, the PROT reflected from the right-hand wall are colliding at high speed with those that have just been emitted, fusing them into HYGN particles (presumably there's some sort of magical proton-to-electron conversion going on behind the scenes). If the reaction continues or if the total impact velocity increases, you get NBLE, CO2, OXYG, URAN and occasionally PLUT and SING