I have been doing a little back of the envelope calculations on the scaling laws for the Bussard Reactor.
Power scales as the 7th power of volume. Reactivity scales as the 5th power. If we assume unit radius and reactivity for a 1 MW unit what will be the relative radius and reactivity for other power outputs?
So control will be a problem with larger outputs due to high gain and sufficient reactivity will be a problem with smaller outputs due to low gain. It will be interesting to see what the actual reactivity is in the test reactor.