The amount of progress over time is a bell shaped curve. For a period of time after the technology becomes practical, it will get more funding & smart people involved. During that time most of the major advanced in the tech will be made. This phase may last a long time. After much of what can be done with it is discovered and optimized, the amount of progress will slow down.

Ah, yes, thank you. I was thinking about the far side of the bell curve after most of the easy gains have been made and bureaucracy sets in.

Once we get it going it will attract lot's of investment, global competition, and mass production. Every fusion reactor you build is essentially a money printing machine and capitalism excels at optimizing the production of things like that.