It means if you want to use only a half wave, then you need to accommodate for this. Yes, if you want to use the Half Wave, then a second core is a good way to do it.
You could use a SCR Cap Inductor discharge, but this is more work again. Time t = R x C
Sorry, I may have confused you at some stage. Using a half wave, suggested here, is a good way to learn the timing. But we must think 1/4 Wave timing. Breaking the waves into Quarter Wave parts:
This is exactly a timing problem.
If I may suggest CD, keep the information, keep this all fresh in your mind, because it is important, but move on to the new thread: Important: Delayed Conduction in Bucking Coils
This thread incorporates all the last bit of information and goes a little deeper into the way this works. Giving you a better understanding of how the Waves interact together, using Delayed Conduction techniques, which are the same, but easier to work with. A much easier way to see how the timing works!
Timing is a critical aspect to these machines, we need to see the interactions between the Waves for their Value.