Paper studies of fusion reactor designs given an availability figure, but this is mere aspiration, chosen because that number is necessary, not because it known to be achievable. The few actual studies of how available a fusion power plant would be (using MTBF and MTTR figures from related technologies) have come to very troubling conclusions: the plant may be operating just a few percent of the time. Getting fusion technology to the point where working reactors aren't perpetually down for repair is even more important than developing materials tolerating higher neutron displacements-per-atom (because it's hard to do the latter without the former). This requires building an experience base with all the kinds of things that will go into a fusion reactor. It also argues for making fusion reactors as small as possible (so there are fewer things to break); this is probably the best argument for these small high field devices (but an even better argument for high-beta plasma configurations).