Ok well here is what I was speculating the function would in the last one.
1. On signal from the switch, R1/Pot would energize the inductor while providing +sin AC through that regions SCR and the second SCR facilitates -sin AC.
2. Once the inductor has reached its peak field current would no longer be feeding the gate of the L1 SCR. Then when the signal from the switch is disengaged there would be another short firing but that is pretty inconsequential.
Normally I would do this with relays, but they are pricey