In order to synthesize antihydrogen, we need to combine antiprotons with positrons. We call this delicate process ‘Mixing’. We want to keep the antihydrogen for study, so we use a magnetic trap to confine (trap) it. The mixing process has been carefully planned such that the magnetic trap does not interfere with it. This allows us to repeat the ‘Mixing’ step inside our magnetic trap to ‘Stack’ (accumulate) antihydrogen in the trap.