Since their ratio is 1:1, each Plasma Exciter-making Assembling Machine can be fed from a single Prism-making Assembling Machine with a sorter, without needing belts.
Compared to almost all other components in the game, Plasma Exciters are needed in a very limited ammount since they are used only in three buildings.
If you decide to automate their production in the early game, use a single Assembling Machine taking them to a storage with only a few slots unlocked. From there they can be taken to craft the buildings as needed.
Later on, the production of the three buildings can be automated, and one or two Assembling Machines making Plasma Exciters will be more than enough for that.